Any way to objectively choose engine? [Archive]

Big Bird

07-29-2010, 07:14 PM

Lap simulation, linked to pointscoring analysis. Can't go past it. You'll learn heaps.

A perfect lapsim will take a year. A simple lapsim will take a day, if that. The perfect lapsim is a refinement tool, for when you are tuning your established concept around a known track. The simple lapsim will give enough info to form your concept, which is what you want at this stage.

Try to answer the following questions:
A 1kg or 1 lb difference in vehicle weight is worth ... points.
A 1hp or 1kW difference in power is worth ... points.
A 1% increase in braking deceleration is worth ... points.
A 1% increase in forward acceleration is worth ... points.
A 1% increase in lateral acceleration is worth ... points.
From the above, come up with rules of thumb like "A 1% increase in cornering acceleration returns ... times as many points as a 1% increase in braking decel".
Your answers don't need to be exact, just good enough to guide your overall understanding of the comp.

With the above, you can then make top level decisions between concepts on a "points per time required" and "points per dollar" basis.

By simple lapsim, think the following: track = straight lines and arcs, lateral grip limit determines corner speed, and start with constant accel and decel. Any track will do. Once you have that working, try to implement power-driven acceleration. Then include aero drag and rolling res if you like. An energy analysis can drive fuel economy comparisons between concepts. Grip limited vs. power limited accel is easy with a bit of thought. All of this can be done simply in Excel.

Remember that the engine has a number of attributes that affect the overall vehicle - weight, power, packaging, economy. Choosing an engine based on straight line accel (for example, selecting only on the "power:weight" criteria) doesn't account for how the engine affects other parts of the track (i.e. when power attribute is "off", but weight, economy & packaging attributes are still definitely "on").

As a team, spend a week performing and assessing the above. Get everyone to the same level of understanding. Choose the most appropriate solution for your resources, put a freeze on it and move on. Either engine choice can be competitive, but your understanding and team cohesion will be hugely enriched by working through the process.

Decision matrices are great when they are populated with quality, (read, quantified and justified) data. But as said above, more often than not they are just formalized guesswork. Most I've seen have been awful and are only used to justify a pre-determined solution.

Cheers,

Kevin Hayward

07-29-2010, 10:31 PM

I agree with Geoff that lap sims are invaluable. You do need to keep in mind that lap sims usually work with a 100% capability of the driver. This can be simply dealt with by applying overbraking (a very common problem) and percentage factors to overall cornering. When choosing fundamentals like this it is good to consider the "best" situation, as well as the "usual" situation.

Lapsims bring quite a bit of objectivity to decisions within the team as Geoff has indicated. There are however a number of other factors that need to be considered in the general design process. Even with respect to the overall performance. A couople of questions include:

How do you assess the points value of ergonomics? (This is very important for things like shifting systems)

How do you assess the points value of reliability? This can be analysed in some depth as a risk assessment.

Add into this mix the higher team level issues. An engine choice for instance locks you in for a number of years if you wish to make the most of your choice. What sort of testing facilities are available? Is one method of construction easier or more difficult for you in comparison to other teams? How will decisions on your car affect funding opportunities?

There has been quite a lot of study gone into accurate concept selection. Decision matrix style devices are usually helpful, but surprisingly the simpler methods work just as effectively as more complex versions. It is much more important how they are implemented in a group setting. Group dynamics being what they are nearly always encourage certain individuals over others. The whole squeaky wheel analogy. It is important to have methods to neutralise egos and have true concerns about one way or another come out.

I would also strongly recommend simple statistical models. Plot out choices of teams vs points scores (in all events including overall). They will show the historical content of how the different decisions finish in the real world. This is likely to show things like reliability concerns as well as highlighting the difference between fastest cars and overall winners. With this approach you may be the team to miss out on being the first to do _______ properly. However there are usually very few benefits to being the first group to do something right for the first time. Look into the history of things like MP3 players and ground effects race cars and you see that the "firsts" usually dont hold an advantage very long at all. Simple statistics are a great help for these decisions. Especially with 400+ cars a year being made.

Finally I think the decision between engines is not a fundamental decision. Your choice between either will not define whether you have a winning car or not. The proof of this statement is in the results from the last few years. You should be focusing your debates on fundamental decisions. Other aspects of your car design will have a massive effect on your engine choice. Is your team capable of building a car well under 180kg for a single? Is your team capable of running a four cylinder car at around 3L for the endurance run?

Answers to these questions (and many others) will help to inform your decision for which engine to run.

Kev

Spetsnazos

07-30-2010, 10:53 AM

Originally posted by Big Bird:
Lap simulation, linked to pointscoring analysis. Can't go past it. You'll learn heaps.

A perfect lapsim will take a year. A simple lapsim will take a day, if that. The perfect lapsim is a refinement tool, for when you are tuning your established concept around a known track. The simple lapsim will give enough info to form your concept, which is what you want at this stage.

Try to answer the following questions:
A 1kg or 1 lb difference in vehicle weight is worth ... points.
A 1hp or 1kW difference in power is worth ... points.
A 1% increase in braking deceleration is worth ... points.
A 1% increase in forward acceleration is worth ... points.
A 1% increase in lateral acceleration is worth ... points.
From the above, come up with rules of thumb like "A 1% increase in cornering acceleration returns ... times as many points as a 1% increase in braking decel".
Your answers don't need to be exact, just good enough to guide your overall understanding of the comp.

With the above, you can then make top level decisions between concepts on a "points per time required" and "points per dollar" basis.

By simple lapsim, think the following: track = straight lines and arcs, lateral grip limit determines corner speed, and start with constant accel and decel. Any track will do. Once you have that working, try to implement power-driven acceleration. Then include aero drag and rolling res if you like. An energy analysis can drive fuel economy comparisons between concepts. Grip limited vs. power limited accel is easy with a bit of thought. All of this can be done simply in Excel.

Remember that the engine has a number of attributes that affect the overall vehicle - weight, power, packaging, economy. Choosing an engine based on straight line accel (for example, selecting only on the "power:weight" criteria) doesn't account for how the engine affects other parts of the track (i.e. when power attribute is "off", but weight, economy & packaging attributes are still definitely "on").

As a team, spend a week performing and assessing the above. Get everyone to the same level of understanding. Choose the most appropriate solution for your resources, put a freeze on it and move on. Either engine choice can be competitive, but your understanding and team cohesion will be hugely enriched by working through the process.

Decision matrices are great when they are populated with quality, (read, quantified and justified) data. But as said above, more often than not they are just formalized guesswork. Most I've seen have been awful and are only used to justify a pre-determined solution.

Cheers,

Thanks mate.

This is pretty much what I was looking for!

I am still in the process of getting some data from my team, but can you guys give me ballpark estimates on what acceleration and deceleration speeds I should be using? Also what is the average and top speed?

Thanks alot everyone. I am going to attempt to do the calculations on the lapsim. If you guys have any other resources that could help I'd greatly appreciate it

Thanks again!

thewoundedsoldier

07-30-2010, 11:10 AM

The rulebook gives track curvature. You could start there to get acceleration and deceleration values.

I think most schools set top speed between 70-80mph and take average track speed to be between 25-35mph.

Spetsnazos

07-30-2010, 11:12 AM

I would also strongly recommend simple statistical models. Plot out choices of teams vs points scores (in all events including overall). They will show the historical content of how the different decisions finish in the real world. This is likely to show things like reliability concerns as well as highlighting the difference between fastest cars and overall winners. With this approach you may be the team to miss out on being the first to do _______ properly. However there are usually very few benefits to being the first group to do something right for the first time. Look into the history of things like MP3 players and ground effects race cars and you see that the "firsts" usually dont hold an advantage very long at all. Simple statistics are a great help for these decisions. Especially with 400+ cars a year being made.

Thanks Kev!

I actually was going to do what you said above but I came to a brick wall when I tried to find out what other teams have been running. Apart from some intense guesswork from random pictures, it has proven near impossible to get an accurate idea as to what the setup was for each team.

Is there a resource to see what others have been running? I was at the competition and when i asked questions from some teams, they either BS'ed me or tried to hide their design. COMPLETELY UNDERSTANDABLE!

Any tips on how I can still do what you mentioned??

Spetsnazos

07-30-2010, 12:07 PM

Originally posted by thewoundedsoldier:
The rulebook gives track curvature. You could start there to get acceleration and deceleration values.

Sweet thanks I found it

as reference if anyone needs it, this is from 2010 rulebook

The following standard specifications will suggest the maximum speeds that will be encountered on
the course.

Average speeds should be 40 km/hr (25 mph) to 48 km/hr (30 mph).

Straights: No longer than 60 m (200 feet) with hairpins at both ends (or) no longer than 45 m
(150 feet) with wide turns on the ends.

Constant Turns: 23 m (75 feet) to 45 m (148 feet) diameter.

Hairpin Turns: Minimum of 9 m (29.5 feet) outside diameter (of the turn).

Slaloms: Cones in a straight line with 7.62 m (25 feet) to 12.19 m (40 feet) spacing.

Miscellaneous: Chicanes, multiple turns, decreasing radius turns, etc. The minimum track
width will be 3.5 m (11.5 feet).

Big Bird

08-01-2010, 04:51 AM

Originally posted by Kevin Hayward:
I agree with Geoff that lap sims are invaluable. You do need to keep in mind that lap sims usually work with a 100% capability of the driver. This can be simply dealt with by applying overbraking (a very common problem) and percentage factors to overall cornering. When choosing fundamentals like this it is good to consider the "best" situation, as well as the "usual" situation.

Lapsims bring quite a bit of objectivity to decisions within the team as Geoff has indicated. There are however a number of other factors that need to be considered in the general design process....

Fully agreed Kev (and nice to see you popping up again on the boards). As when you write such things you wonder when to stop, and given my post above was done on the way to work I left out the whole "potential vs execution" thing. (I've already bored everyone with that point on another thread anyway).

What I find valuable about writing such simulations is not so much finding out which concept offers the greatest performance potential - because with the quite complex FSAE rules most of the better concepts are within a few points of each other anyway. Rather it is the reality check and the sense of priority that the exercise offers. As I've said many times before, if you are finishing 300 points behind the winners, and you find your concept's potential is within 10 points of the winners, then you realize labouring over vehicle concepts ain't going to get you very far.

The driving force behind RMIT's change to the 450 single concept wasn't a performance potential advantage - in fact all of the sims I've done indicate a UWA style car is worth around 10 points more than an RMIT style car. Rather, we wanted to address a problem we had completing the event. We thought about some alternative concepts, checked they were competitive enough (even if they weren't necessarily the top ranking option on the sim) and then chose an option that we thought best aligned with our resources and skill base.

Cheers, and good luck Spetsnazos

Kevin Hayward

08-01-2010, 06:48 AM

Geoff,

I remember some discussions we had in 2004 (great year for the Australian comp). I came away thinking that for all we had done that you guys had come up with the better concept. Unfortunately I think the beauty of that original composite single from RMIT is still missed. The fact that you could get similar performance by doing less was really impressive.

At the time I ran through the numbers and couldn't see that a single had higher performance, and we had a known quantity with our concept (with a few years of continuous development mapped out). UWA has considered the single cylinder option quite carefully and come very close to switching a couple of times. Usually for the reasons of rear end simplicity.

In 2004 I would have said you couldn't do much better than a well worked out 4 cylinder with a spaceframe. Not far from the truth given that Woolongong won 2004 Australia, and Cornell won 2005 US. Both spaceframes with turbo charged 4's.

However rule changes (and development in singles) over the last few years have favoured both composite chassis construction and single cylinder engines (or rather fuel efficient cars). I don't think its been a huge points swing, but probably enough to put the favourite in the single and composite camp.

I would run the numbers through the sim again, but I think my power curves for singles would be a gross underestimate of what some of the teams are squeezing out now. Seeing the GFR car powersliding at Silverstone was quite impressive.

In all this conversation though your point about resources and skill bases is the most important. I am now involved as Faculty advisor at Edith Cowan University. It is quite a different environment to UWA, both with the type of resources and students available. I have no doubt that the team has the potential of becoming a top level team, but it wont be able to so by following a UWA (or RMIT) style car.

Kev

Big Bird

08-02-2010, 02:14 AM

Hi Kev,

We've really run away with this thread. Two old codgers reminiscing about better days... Well, one old codger at least.

Re: "Unfortunately I think the beauty of that original composite single from RMIT is still missed". I'd agree, and go as far as saying that it is even missed within the team. The original design philosophy was that by building a simple car, and getting it done early, we would have more time for the things that matter (namely understanding handling, shocks, tyres). I would have thought by winning a few events we might have convinced those within the team that the car itself was fine. But unfortunately for a few years there technomania took over - and rather than objectively assessing where efforts were best directed, team focus moved more towards "what can we make out of carbon fibre next". So the team started chasing the incremental stuff, while neglecting the basics.

I think it is hard for a new team to be convinced to leave good enough alone. Our culture drifted towards looking at what last years team did, and then doing it all again - a sort of component redesign project ad infinitum. If last years team built their car by having two guys optimizing the chassis, one on pedal tray, one on hubs, etc, - then this year's team gets guys optimizing the chassis, another on pedal tray, one on hubs...

So the project areas that are getting focussed upon are only getting incremental gains (usually pushing towards fragility), and the areas of greatest potential points return and least present development (i.e. the "lowest hanging fruit") get neglected.

I agree that the comp rules are swinging towards the singles, considering the new fuel economy rules, and a team that does it properly is going to be hard to beat. I say this with a heavy heart....

I don't necessarily believe that composite tubs are necessary though. The event still rewards low cost, and this partially compensates for perceived performance gains of composites. I think in this case the more critical factor is the psychological one. The general masses see UWA / RMIT / TU Graz / Stuttgart or whoever doing well with composite tubs, and the correlation is made that carbon is required for success. This drives their teams to overstretch their resources and skillbase (whether it be an attempt at a composite tub, or other tricky features to somehow "compensate") - and we end up with a few competitive teams doing well and a lot of non-finishers.

I'm glad to see ECU doing well with their more traditional car - I have no doubt this is driven by objective engineering analysis and a heavy scepticism for fashion and fancy. Keep up the good work Kev.

Spetsnazos, some figures I've used as inputs and checks in my lapsims:
1: Tyre longitudinal and lateral grip coefficient - around 1.4-1.5 continuous as a starter
2: Top speed around 110kmh
3: Average speed around 45-55kmh
A hint for "design for fuel economy" - consider the difference between points 2 & 3 ...

Cheers all,

Kevin Hayward

08-02-2010, 07:33 AM

Spetsnazos,

I got a hold of the results from the latest student event and correlated the results with the number of cylinders from each car for some simple statistics.

First of all I assumed that we would only consider cars that competed in at least one dynamic event. As a scrutineer it was clear that cars that were failing tech were not doing so by the choice of their engine. Some may argue that one type of engine is simpler or more difficult than another.

60 cars finished at least one dynamic event. This was made up of the following:

44 Four cylinders
7 Two cylinders
9 Single cylinders

The average scores:
4 cylinders - 374
2 cylinders - 195
1 cylinder - 457

DNF percentages:
4 cylinders - 59%
2 cylinders - 86%
1 cylinder - 44%

One thing that was apparent with these scores is they include a lot of low scoring teams. These teams probably do not reflect the performance advantage/disadvantage of the engine.

Looking at the top half of the teams the following averages result:

The average scores:
4 cylinders - 563
2 cylinders - 379
1 cylinder - 522

DNF percentages:
4 cylinders - 27%
2 cylinders - 100% (only one team)
1 cylinder - 29%

This is probably still not reflective of the performance/reliability difference of the types of engines. the 30th place team only scored 293 points. At this point it is quite clear that the engine choice is not worth nearly 500 points to the lead.

Looking at the top ten we see:
9x 4 cylinders (average score 736.8)
1x 1 cylinder (score of 726.8)

If we eliminate any endurance DNFS we might be able to see a trend in performance only.

Finishing cars:
1x 2 cylinders (223 points)
5x 1 cylinder (av. 520 points)
18x 4 clynders (av. 604 points)

...

From this simple study of the single event I would probably conclude the following:

- Twin cylinder engines have seemingly poor reliability and no clear performance advantage

- When looking at a reasaonable selection of higher performance cars the singles and fours have similar reliability, with a possible points advantage to the four cylinder cars.

There is one small point missing from this quick analysis is that the two quickest cars in autocross were both running singles and both DNF'd. Had they finished the analysis would look quite different (likely with a different overall winner).

I think the main conclusion, one of which both Geoff, myself, and many others have previously concluded is that there is actually very little difference in overall points haul between the singles and the fours.

This sort of analysis done over a number of events will improve the reliability of results. Looking at the top 100 teams in the world rankings would give a really good picture of the reliable performance difference between the concepts.

Kev

Kevin Hayward

08-02-2010, 07:46 AM

Geoff,

Would love to be able to take credit for ECU doing well, but the team has been filled with very practical guys with their egos and car fantasies well in check. The team makes it very fun to help out, and are quite patient with the confused ramblings of an old codger.

As for composites I would agree that they are not necessary even though they offer a distinct (but smaller than many think) advantage. The results are skewed quite heavily in the favour of composite teams. This is probably because any team that is capable of putting together a proper equivalency report is capable of building a reliable car.

The composite choice is taken to lightly by many teams. The basic recipe I figure for a successful composite car (from the moment of making the decision) is this:

Year 1 - Figure out how the processes work. Make test pieces and make sure you can meet equivalency. Run a spaceframe.

Year 2 - Make your first composite car. Have problems with good cures, effective packaging, and phantom weight. Equivalency report feels like tearing your eyes out with a spork. Car underperforms.

Year 3 - Bask in the glory of composite manufacturing. Your methods are good, it is easier to make the tub, you enjoy not having to make heaps of bodywork. The spork is put back in the draw, and the car starts to feel like an improvement is made.

Year 4 - Start to complexify.

I was going to publish this process as a paper, but I think it is accepted knowledge now.

Kev

Mikey Antonakakis

08-02-2010, 07:56 AM

In my much less experienced opinion, you can break it down fairly simply to this: Driving fast in an autox has less to do with how much torque you have available at any given time, especially with cars like ours (even low-power cars have very high power:weight ratios), and more to do with how well they can be driven. Try to find autox and endurance layouts (perhaps in the program guides) to see how much time is spent on straights, and how much is spent on decreasing-radius turns, slaloms, and chicanes, where power isn't that important, but rather control of what power you do have. I could go on and on but I think everyone has said everything I'd have to say already. But I will stress this: get the car driving early so you figure out what will break. Your engine choice will be affected by this goal. For example, here at Columbia we've had a car competing for the last three years straight (first three years we've run dynamic events with cars). Each year the design of the car has improved, and each year the cars have gotten faster and more reliable, but each year we were finishing the car as we packed the truck for competition. This year was our lowest-scoring, because we missed accel and skidpad, and DNFed on endurance. We would have most likely finished endurance had we run the car for more than a few minutes prior, and noticed the single (out of many) small non-reinforced plain rubber cooling hose that exploded two laps before the driver change. The car was running pretty well, I think we lapped almost everyone in our run group, and we only had 44whp (something wrong with that engine). From the lap times we were running, we probably would have had an overall score putting us somewhere around 30th in the competition had we finished endurance, as compared to the around 80th we actually ended up finishing. So, make a logical choice on your engine, build your car, test it, compete and do well.

Spetsnazos

08-02-2010, 10:36 AM

Great replies everyone thanks alot and keep them coming!

Do-it-Guy

08-04-2010, 04:00 AM

@Kevin

Interesting approach! But honestly i don't think that this analysis will work just based on statistics. I think you have at least to take the individual reasons for the DNF's into account. Otherwise the result maybe as good as comparing the migration of storks to birthrate of humans. Although you may find a coincidence, you will never know if you can trust it. And this is also independent of the number of teams you take a look at.

Christian
Teamleader Engine and Drivetrain 08/09
High-Octane Motorsports
Erlangen U

Kevin Hayward

08-04-2010, 05:15 AM

Christian,

I personally wouldn't do this analysis just on the statistics, but I think the results are incredibly indicative of the actual answer. Statistical analysis is an incredibly accurate way of looking at very complex problems. In this case the main problem with the approach is the small numbers of some choices. Looking at all the cars in the world (400 or so) would improve this. More data, more trust in the results.

I think if you did a student t-test using the mean and std. dev you would notice that the difference between singles and fours is negligble in both reliability and performance (within the margins of error of the stats), but the clear result of the twins would hold.

The actual problem is very complex as your engine choice affects the following:

- Overall vehicle speed
- Fuel economy
- Cost to build the car
- Effort to build the car
- Reliability of the car
- Ease of design of rear bay
- Design time
- Testing time
- Number of team members required to do a decent job
- Interactions with rear suspension
- Relative difficulty of cooling system
- Difficulty of oiling systems
- Effectiveness of vehicle launches
- Underbody aerodynamic potential

And many many more. Some of these are meaningful, some are less so. Some can be address with analysis with a lap time, some not. Statistics is used quite a lot in mainstream engineering, and massively underused by FSAE teams. In these complex problems it is a very useful field. Treating DNF's as special cases limits the usefulness of the results you gain.

Sure team x may have failed because the suspension broke. But did this happen independent of the engine choice? Perhaps the supercharged twin cylinder engine required a large amount of the teams resources (time and money) that were diverted away from suspension design and development.

With so many teams out there at the moment I think statistical approaches to the data is more valuable than ever. If we imagine that every car is a test point in a large DOE project it becomes quite clear. Plotting choices against performance allows you to identify strong or weak correlations between those choices and performance.

Care must be taken when making distinct cause-effect statements that are not necessarily true. If we take the twin cylinder example think of the two possible statements.

1) Twin cylinder cars do not do well in competition.

2) Twin cylinder engines are not a good design choice for FSAE.

The first statement is quite easy to test, and very much a true statement. The second may or may not be true. I would say that the first statement being true makes it more likely that the second is also true.

Now looking at similar statements for Spetsnazos:

1) There is little difference in the performance between a single cylinder car and a four cylinder car.

2) Neither a 1 or 4 cylinder car has a significant performance advantage with the current rule set.

The first statement is currently true. The second may or may not be true. However there is significant evidence to suggest that it is.

I have created a fancy lap time simulator, run simulations back to back. I have done costings and estimates on man hours for different solutions. I have talked endlessly with others that have tried different solutions. A lot of effort to come to the same conclusions as a 1 hour simple statistics analysis of large FSAE comps provided.

Having been involved with this thing a lot it is amazing to see how many decisions are not made by reasoning (statistics, simulations) but rather by ego and ignorance. It is far to easy to look at the teams using a concept you are interested in and imagine the only reason that they are struggling is that they do not have your magic insight. I have done it myself too many times.

Kev

Kevin Hayward

08-04-2010, 05:22 AM

Christian,

I note that your team ran a twin cylinder engine. My post was not meant as an insult to teams that run a twin cylinder, and I hope you do not view it as such.

The results are what they are. The Aprillia engines have had a horrible reliability problem in FSAE cars. Event after event since their introduction into the competition has shown the same result.

I hope that your team (and others) find solutions to the problems and change the analysis. They have some very big advantages to anybody that can get them to work well, but I'm just not sure its worth the effort.

Kev

thewoundedsoldier

08-04-2010, 05:37 AM

It seems like a lot of smoke just to say something along the lines of "well...we saw team x doing it so we thought it was a good idea".

I think the only reason this would work for you, Kevin, is because you have done all the other analysis and estimation of resources so you have a clear understanding of the big picture. I would be afraid of people contorting your argument to mean that they can make design choices based off of statistics alone.

If we were to only ever look at everyone else, who would ever try something new?

I must say that this has turned into a pretty cool thread.

Kevin Hayward

08-04-2010, 06:59 AM

Your first line is exactly right. But I don't see what is wrong with it. <STRIKE>However I think you make the mistake of assuming anything in FSAE is new.</STRIKE> (Edited to cross out ridiculously arrogant statement)

I have also stated in previous posts on this thread that it is a tool to be used along with other tools.

We all want to beat other teams with a better idea, rather than just beat them with a better team.

Kev

Kevin Hayward

08-04-2010, 07:26 AM

I can't let this issue go it seems.

Statistical methods can be used to answer straightforward questions. I propose 2 questions:

Is a single significantly better than a four? Look at the results. There are enough teams out there to make a reliable judgement call.

Should I run 4wd? Looking at the results there are not enough teams that have run 4wd systems to make the call using statistics. This is one for the analysis.

In the original question of the thread there was no suggestion of someone proposing a new engine to be run.

I also add that it is important to understand the norms, but analyse the outliers. The most significant outlier in this decade has been RMIT. They were the first single cylinder car to be truly successful. At the time they started down the line you could not make a call on the performance on singles based on statistical methods, because the numbers of teams running them was not sufficient. The most famous other team running a single at the time was Delft.

Anaylsis of the RMIT concept, using some simple parametric tools would have yielded some interesting information. While there were other teams running singles they appeared to carry a fair bit of extra weight, especially compared to the featherweight Delft. This raised an interesting question:

Why was this car with a single cylinder engine finishing well when it did not make the most use of light weight of the single cylinder engine?

If you answer that question you get to the secret of their success. One which Geoff has been so kind to share with anyone who asks.

So when you want to try something new statistics have limited use. However if you are planning to make a choice between options that other teams are using then check the results.

Kev

thewoundedsoldier

08-04-2010, 08:39 AM

So when you want to try something new statistics have limited use. However if you are planning to make a choice between options that other teams are using then check the results.

"If every winning FSAE team jumped off a bridge,..."

One problem I have with your method is that it leaves the "follower" team two steps behind the "leader" team. That "leader" team is not there because they chose one thing or the other. They are there because they committed to a concept, got it sorted out, and didn't care about what the field was doing in the meantime.

With respect to engines, the only realistic choices aren't changing anytime soon. But beware of using this methodology for other parts of the car. By the time you get your design to wherever the field is at, the field will have picked up and moved somewhere else.

Again, Kev, I don't mean to argue with what you are saying. I just know that prospective FSAEers might not have the experience you have, and could take your proposed method as a green-light to not do their homework properly.

Thomas MuWe

08-04-2010, 12:49 PM

@kev:

Somebody else said to me the other day:
In Racing you should not look necessarly what the others are doing. If you do so you are benchmarking. But the ultimate goal is to be the benchmark! And to look at other teams or concepts often makes your horizon smaller.
But I think you made some pretty good arguments in this thread as well es Geoff whom I not know but IMO is the benchmark http://fsae.com/groupee_common/emoticons/icon_biggrin.gif in this forum in terms of intelligent comments and straight forward analysis. Sorry Pat!

@the original topic:
I am working in a field with objective arguments. It is still a subjective thing behind everything there. Because your reference system is not something god threw on the earth, it is made by people and as a result subjective. Statistics are helpful in one or the other way.
What I like about FSAE is to have this wide spread of concepts / engines. We had - with our supercharged 450 - a special engine in FSAE. That is quite cool. And if you look at our design results in the past 3 years our team was in every design final independent from the comp. In particular at FSG which is a pretty good benchmark, we finished 3rd, 3rd, 2nd the last three years. But we were not able to come over 800 points since 2007.
Objectively we should change our focus away from extremely good design results to being fast in AutoX/Endurance where you can get more points, maybe changing to a NA 450 with 10" rims. And then, maybe a little bit of passion and pride will go away, so I don't think this will happen.
What I want to say then is:
Get the most out of your concept and do not look at all the others and be jealous. Be the benchmark whatever this means to you. :-)

Cheers,

Thomas

suspension jr08 / jr08evo
joanneum racing graz

Spetsnazos

08-05-2010, 05:32 PM

Wow this thread has been going exceptionally well. Thanks again guys http://fsae.com/groupee_common/emoticons/icon_smile.gif

ZAMR

08-11-2010, 08:58 PM

I really like this thread as well, good stuff.

I would like to defend the Aprilia a little bit though. The failures of the other teams that run 2 cylinders seems very disheartening I know. In fact I believe OU may be the only Aprilia success story in all of FSAE. Since 2009 we have had our best finishes with a twin cylinder:

2nd place FSAE Virginia 2009
5th Place FSAE West 2009
2nd Place FSAE West 2010
8th Place FSG 2010

We have never had this kind of running before. Granted, we've had our fair share of bad luck with the ape, but also a lot of good luck. If you are smart with it, and know its perks and its drawbacks, and dont treat it like any regular old motor (it certainly is NOT), you have a good chance of making a good car.

All this being said myself and a teammate are going to try a lapsim like the one you guys have been talking about tomorrow based off of the lateral and longitudinal sims we have built already. I'm sure we'd be more than happy to share what we find. I'd also be interested in what you guys come up with!

Do-it-Guy

08-12-2010, 02:46 PM

Kevin,

sorry for my late reply, I went to Hockenheim to watch a single cylinder victory, scoring 866 points (Well done Delft!) and sadfully to watch an Aprilia DNF (which doesn't really help my argumentation...) http://fsae.com/groupee_common/emoticons/icon_frown.gif

Good detective work btw. figuring out that i'm from one of the few teams that believe in the success of 2-cylinder http://fsae.com/groupee_common/emoticons/icon_smile.gif

I'm not insulted by any means by your statement. Far from that, i enjoy this discussion from quite a neutral point! :-) I totally agree with your list of engine choice affects, but I also agree with Thomas that a choice only based on statistics won't work. You said yourself that this approach wouldn't work for the 4WD because of the small numbers. Are the numbers of "exotic" concepts like a 2-Cylinder or a supercharged 450 single so much bigger? What is in your opinion the minimum number of cases to make a statistic approach significant?

In McBeath S.'s Book "Competition Car Preparation" it is said that the influence of the engine to the overall performance of a racecar is just at about 20%. And I also like the quote of Scuderia Ferrari's head of engine and electronics Luca Marmorini: "It is difficult to win a race just because of the engine, but easy to lose it because of the engine"

According to this I think you have to look at the real reasons for a DNF in detail if you want to find a significant connection between (not) scored points and the number of cylinders. A (sad) example is the DNF of my (former) team at Silverstone: At first sight it was an engine failure. But if you do a 5-Why analyis you will find out that is was basically an assembly error or a lack of knowlegde flow inside the team. (Some screws connecting the timing wheel to the fly wheel weren't secured properly with loctite, bad desgin by Aprilia btw.) You can't blame the numbers of cylinders for that! Another example: If a team hasn't the knowlegde to design a proper cooling system it will mess up every engine independend of it's number of cylinders.

One (not mentioned yet?) reason for the great reliability of the inline 4s maybe the fact that you run them below their maximum (stock) power because of the restrictor. Pushing a small single or two cylinder to the limit to make them competitive will of course decrease the reliability and result in more DNF's.

Best Regards,

Christian

Kevin Hayward

08-12-2010, 05:48 PM

Christian,

The big problem in using statistical methods is in incorrectly assigning reasons to the results. The number of twins is very low (although collecting multiple comps may help there). There are some methods to check whether the number is too low for the result to be significant, the student t-test being one. Obviously the info I presented was a very basic analysis of limited data.

Your reasoning for the reliability is very sound. The number of cylinders used is not the problem, rather the reasons likely lie with the engine construction. My basic thought process for the reasons behind the reliability are very similar:

Aprilia - Will be used very close to the engines original performance level. The engine also has a few surprises (inbuilt faults, or limitations) that students need to be well aware of to use the engine effectively. Complexity of intakes, exhausts and cooling is not much less than a four.

Singles - The reliability of these engines come with their simplicity. Even though they will be used at closer to their operational limits they are much simpler to work with. Complex plenums and exhausts are not needed which frees up time to work on getting the engine running properly. Power output is also a little lower meaning cooling systems are a little easier as well.

Fours - The big reliability advantage here is that they are being run so far below their operational limits that they can handle a lot of abuse. They can be run hot, lean, and with low oil pressure for significant periods of time without serious damage. The big disadvantage comes in the complexity of the associated systems such as plenums, exhaust, cooling, and oil sumps. While these often don't mean a non-running engine they do mean that it is difficult to get good performance (including fuel usage) out of them.

Personally I wouldn't be looking for a win from an engine advantage. I used to look at three main areas of the car and what the groups should have their main focus on:

Chassis - Being the main structure of the car this group must consider integration above all things. This group needs to know about every system on the car, and the members should be actively involved in construction.

Suspension - This is a mechanical grip competition. Most of your performance of the car will come from this area. They must also be the main advocates for low weight.

Drivetrain - This is the most complex area of the car. This group must focus on reliability and event finishing. People from this group must form a large part of your pit crew.

Other subsystems would fit under these groups as need be.

Kev

J. Vinella

08-12-2010, 06:17 PM

Good to see some old cogers on the board again. All we need now is Z to come back in and throw something out radical to complete the Australian trio. Single, 4 banger, jet pack.

One of the better threads I have read on this forum in a long time. Thanks guys.

J. Vinella

08-12-2010, 06:21 PM

Originally posted by Thomas Müller-Werth:
And then, maybe a little bit of passion and pride will go away, so I don't think this will happen.
What I want to say then is:
Get the most out of your concept and do not look at all the others and be jealous. Be the benchmark whatever this means to you. :-)

Cheers,

Thomas

suspension jr08 / jr08evo
joanneum racing graz

So true. Remember folks, it's not the skill of the people, or how many you have, it's how they all work together and how much fun they have doing it.

Big Bird

08-13-2010, 09:31 AM

This has certainly grown into quite an entertaining thread. And yep, I too would welcome a return of Z to the boards. But Z was smart enough to know when to stop...

A few quick responses if I may:

Christian - "One (not mentioned yet?) reason for the great reliability of the inline 4s maybe the fact that you run them below their maximum (stock) power because of the restrictor".
Kev - "Fours - The big reliability advantage here is that they are being run so far below their operational limits that they can handle a lot of abuse".
We certainly discussed the whole redundant mass / robustness issue when we were choosing an engine, it is a strong argument. What I find amusing though is how we would rarely consider applying such logic to other areas of the car. Do we ever hear "Yeah, steel wheels / cast iron uprights / Toyota Camry brake calipers... - the big reliability advantage here is that they are being run so far below their operational limits that they can handle a lot of abuse". (Apologies to you Kev for twisting your words out of context - you are one person who definitely would think of such statements critically). I always felt the engine held a sort of romance to us racing types, and we treat the topic with a bit of reverence. Which of course makes it a prize target for a bit of objective re-analysis.

Christian - "Pushing a small single or two cylinder to the limit to make them competitive will of course decrease the reliability and result in more DNF's". A shame many believe this to be necessary. You don't need to push them to their limit to be competitive, neither in terms of power or weight. (We've been perfectly competitive in the past with a 200kg 50hp "porker"). This whole over-compensation thing is deeply rooted in what the shrinks call loss aversion - (e.g. the pain of losing $20 has a greater impact on us than the joy of finding $20). To me the benefit of a 450 single was that by trading off a bit of straight line speed we were buying shortened manufacturing and development timelines, the reliability of an almost standard "off-the-shelf" FSAE engine, and better fuel economy - all critical issues to us. To then try to buy back the speed by selling off reliability & economy, and sending manufacturing and development times northwards again, just all seems a bit confused to me.

I think the effect of engine choice in our situation is a bit more than the 20% that McBeath quotes (and remember his case study was motor racing - FSAE is a completely different kettle of fish). It seems to me he was speaking of classic performance attributes, whereas in FSAE it is often the secondary effects (especially time and budget impact) that are critical. And to me, above-quoted problems such as assembly errors and knowledge flow problems are fixed by better time management.

Cheers all, and lets keep this sort of chat flowing.

Hub

08-13-2010, 02:25 PM

Hello,

For our first car the engine choice was not driven by the advantage we will take in term of performance and points. It's probably our lowest priority. As a First year team I think it's more important to choose an engine that could be found easily and at low price in the after market. 1 and 4 cylinder engine have shown comparable performance on track. But our Hornet engine is one of the most sold engine in France, so we could find it for low price and there a lot a spare part available. Also as previously said, it's better suited for an heavy car. Compared to other 4 cylinder like CBR engine the Hornet is more suitable for the restrictor.

Jan_Dressler

08-14-2010, 07:42 PM

Hi Kev,
I really like your analysis. Some issues:

Originally posted by Kevin Hayward:
Singles - [...] Complex plenums and exhausts are not needed which frees up time to work on getting the engine running properly.

I am not very familiar with 1-cyl plenums and exhausts as my team uses a 4-cyl, but walking around in the pits at Hockenheim and the Italian events for the last two years, I saw some solutions which were not that simple... Resonators in the inlet systems to achieve a more steady flow through the restrictor etc.
Obviously, you CAN do it simple, but when you want to push it to the limits, I think it is not necessarily less complex than a multi-cylinder solution.

Originally posted by Kevin Hayward:
Fours - [...] The big disadvantage comes in the complexity of the associated systems such as plenums, exhaust, cooling, and oil sumps.

Why is the cooling system of a 4-cyl more complex? Okay, you have to use a larger radiator, which is more difficult in terms of packaging, but other than that...
Concerning lubrication systems: Right, you have to develop a decent system. Once. I designed the dry sump system for our car for the 2008 season. It worked, and since then, only minor changes were made every season which didn't afford much time.

Personally, I think the big disadvantages of a four are its weight and size, while the advantages are power (even with not-that-complex solutions) and, above all, reliability and ruggedness, as you said, you can abuse it quite a lot.

I agree with basically all the other things you said http://fsae.com/groupee_common/emoticons/icon_wink.gif

10-27-2011, 07:37 PM

Quote from Big Bird "But Z was smart enough to know when to stop..."

Hmmmm, smaaaart... http://fsae.com/groupee_common/emoticons/icon_confused.gif

The doctors say I'm getting even better now. I can dribble out of both sides of my mouth, at the same time!

And they've let me play with one of these interweb box thingies again. Good for the walls they say. I'm not banging my head against them nearly as much these days... http://fsae.com/groupee_common/emoticons/icon_smile.gif

---------------------------------------------------------------------

Smalltalk over, you're doing a great job Geoff, here and on the "Reasoning..." thread. I've got a few comments I'd like to add to these two threads over the next few weeks. But right now I've got a pot to stir on another stove (nice cooking metaphor, eh?).

----------------------------------------------------------------------

Briefly on the subject of objectively choosing an engine my thinking is as follows.

From the big picture point of view the engine is really just a very expensive, very unreliable lump of ballast, but unfortunately necessary to make the wheels go round. As such, it should at least be the right shape to package neatly.

To me, most engines-drivetrains in FSAE are the wrong shape.

More later.

Z

-------------------------------------------------------------------------

PS. Apologies for not replying to those who've PM'd me over the last few years. The nice doctors thought it would be much better if I just played in the garden... http://fsae.com/groupee_common/emoticons/icon_smile.gif

Mike Cook

10-27-2011, 07:42 PM

holy shit. he is back.

Big Bird

10-27-2011, 08:56 PM

This is bringing a tear to my eye. A happy one. Stir that pot, Z, stir that pot!

Now to drag back Charlie, and Denny Trimble, and James Waltman, and Travis Garrison, and Kirk Feldkamp, and Michael Jones, and ..............

PatClarke

10-27-2011, 10:04 PM

Oh Geoff,

Those are the 'Old Days'. Get with it and appreciate the pithy and informative posts recently from Ftorque, bishoY, rohitkj, deepakthakkar, adham_nabil, lcy1989, akshay verma and shrikkanth, amongst others http://fsae.com/groupee_common/emoticons/icon_wink.gif

Oh, maybe I need some of Z's (electroshock?) treatment...

Cheers

Pat

Mbirt

10-28-2011, 09:11 PM

Originally posted by Big Bird:
Now to drag back Charlie, and Denny Trimble, and James Waltman, and Travis Garrison, and Kirk Feldkamp, and Michael Jones, and .............. The great ROB WOODS!

ZAMR

10-28-2011, 10:06 PM

Originally posted by Mike Cook:
holy shit. he is back.

I didn't know you could say that on the forums...

RyMan

10-30-2011, 07:15 AM

holy shit. he is back.

I thought the same thing myself. Waiting intently for those responses Z. The next generation of students/racecar addicts could use them.

11-07-2011, 07:58 PM

Essay 1: What is the Right SHAPE for an FSAE Engine?
================================================== ==

Earlier I claimed that most FSAE engines are the wrong shape. Here I attempt an objective analysis of what is the right shape for the engine. To do this, first we have to consider what is the right shape for the whole FSAE car. Note that this is primarily determined by the shape of the typical FSAE track, which is very tight and twisty.

Let's start with WheelBase and Track. Full-sized race cars, from Le Mans/Indy (~3.0m x ~1.6m) down to F-Vee (~2.3m x ~1.3m), would probably have to back up a few times to get around an FSAE track. That is, they are too big. At the other end of the range is the FSAE mandatory minimum WB = 1.524m, and a practical minimum T = ~1.1m, below which the car falls over when cornering. The tight, twisty nature of FSAE tracks strongly favours the lower end of this range. So, in round numbers, "manoeuvrability" demands WB = ~1.6m and T = ~1.2m.

Next, we note that these tight, twisty tracks require a lot of rapid changes of direction. Mechanically, this means a requirement for high yaw acceleration, which, in turn, means maximum yaw couple applied to minimum yaw inertia. In simple terms this means "a wheel at each corner", or "all masses inside the wheelbase". Furthermore, the horizontal acceleration following the changes of direction (forward and backward, but mostly sideways) requires CG as low as possible, and front:rear weight distribution between 50F:50R and 30F:70R. So, "agility" demands minimum yaw MoI, minimum CG height, and weight distribution ~40F:60R.

Now consider the layout of the major components required to achieve the above. The wheels, being far from the CG, should be of minimum mass to minimise yaw MoI. (Note that "unsprung" mass over bumps is relatively inconsequential, because of negligible bumps!) The largest single mass is the driver, and to minimise yaw MoI this component should have its CG as close as possible to the overall CG. The engine is the second largest mass, and likewise should be close to the overall CG. Since driver CG is roughly at the navel, and assuming engine behind the driver, this means driver's feet roughly on the front axle.

To me the greatest flaw in the "standard model" FSAE car is that the driver is far too far forward. This is a direct consequence of the excessively long standard engine-drivetrain package, consisting of tall motorbike engine with forward leaning cylinder(s) and longish chain drive to the rear axle. This package pushes the driver a long way forward, and leaves a triangular void between the engine and backward leaning driver. This void is usually filled with lightweight odds and ends, but this is where the overall CG, and all the densest components such as the engine, should be.

The standard FSAE car is a dumb-bell when it should be a cannonball. I remember pushing this point 6 years ago, when I was last here, but very few teams have gone in this direction. A notable exception was Geoff Pearson's RMIT car of that era, which was moving in the right direction, and was very successful. My feeling is that if FSAE was really "a life and death evolutionary struggle for survival", then the standard FSAE dumb-bells would be long extinct. They would have been eaten by the more agile cannonballs.

Why are there still so many dumb-bells around? I see two reasons. Firstly, it is blindingly obvious that a car with a 3m wheelbase won't be fast. Too many 3 point turns!. Likewise, if the CG is too high the car keeps falling over. So WB, T, and CG height are about right. However, too large a yaw MoI only manifests itself as a fleeting dynamic phenomenom. Blink and you've missed it. What you see is the standard car going through the slalom at a certain steady speed. All looks well. But what you miss is that if the yaw MoI was lower, then the front tyres would have to exert a smaller force each time the car changed direction, and speed would be higher.

Secondly, we should never underestimate the power of "fashion" when it comes to decision making. Engineers like to think of themselves as rational, logical creatures that do things for cold, hard, objective reasons. Utter codswallop! I will leave this for another rant, but the standard engine-drivetrain package is pure fashion. It is "what everyone else is doing, so it must be right". An objective analysis shows this to be false. This type of analysis is covered in more detail in Geoff's "Reasoning..." thread, but briefly a simple analysis of a point mass racing around a straight-line + circular-arc track goes a long way to showing what you need to win. However, yaw performance requires consideration of the transitions between different radius circular arcs, which means consideration of a 3-D car. This is not much harder, but it may be the extra step that many teams are not taking. Try it!

So what shape should the engine-drivetrain package be? With WB = ~1.6m and the driver's feet on the front axle, there is an available "engine room" behind the driver and in front of the rear axle of about 0.5m square in plan view, by 0.2m high, bevelled at 45 degrees at its front face. What available engine-drivetrain packages fit this shape? If the car was an EV the designers might put the electric motor near the differential, and fill the rest of the engine room with N hundred tiny lithium-whatever batteries. But considering off-the-shelf ~600cc IC engines, there are hardly any that fit this shape.

So, what to do? Well, no FSAE team buys an off-the-shelf chassis, because they are all too big. So the team builds their own. Likewise, it is not that hard to build a bespoke engine, or at least modify an existing engine so that it is the right shape. I will go into more detail later, but it is really only a few engine cases that have to be modified or made, and most of the internals can be off-the-shelf.

Possible "right shape" engines are lay-down singles or parallel twins, with longitudinal or lateral cranks. Or longitudinal crank flat twins, or possibly V-twins (bit high). More than two cylinders is unnecessary, and has disadvantages. Only lightweight engine components should be outside the engine room, so intake pipes and air filters can poke upward. But all dense components should be inside the room, or else low down and close to the CG, such as either side of the driver's hips.

As examples of suitable bespoke engines see Race Engine Technology March/April 2011 for the UCLan flat-twin, and May 2011 for the Oxford-Brookes V-twin (or find them on the interweb?). IMO both these engines are unnecessarily complicated, but they are the RIGHT SHAPE.

To sum up, the engine is just necessary ballast, a bit like an EV's batteries. To do well in FSAE you have to get the overall package right. Off-the-shelf motorbike engines don't package right. There is a whole lot of nonsense on the standard chassis that does nothing for overall performance but absorbs a great deal of your resources. Throw away your billet machined, platinum plated, titanium suspension whatsits. They are a waste of time and money! Better to spend your scarce resources getting the engine into the right shape so that it packages neatly. Then put it into a very simple chassis, and start wearing out tyres. That is, have more fun. http://fsae.com/groupee_common/emoticons/icon_smile.gif

More later (namely, How Much POWER is Enough?)...

Comments and criticisms cheerfully accepted. http://fsae.com/groupee_common/emoticons/icon_smile.gif

Z

Big Bird

11-07-2011, 09:31 PM

Thanks Z for the kind words, and for shaking up the forums a bit too. These boards have become mind-numbingly dull at times. Unfortunately I'm head-down, butt-up marking assignments right now, but I will respond to your various posts as soon as I can.

Keep up the good work!

Adambomb

11-07-2011, 09:55 PM

Z, perhaps something a bit like this? I'm a huge fan of the package, solves all of the problems you mentioned and it certainly looks achievable. Dazz, anything come of this lately?

http://fsae.com/eve/forums/a/t...=939101563#939101563 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/112101343?r=939101563#939101563)

Jan_Dressler

11-08-2011, 01:03 AM

Originally posted by Z:
So, what to do? Well, no FSAE team buys an off-the-shelf chassis, because they are all too big. So the team builds their own. Likewise, it is not that hard to build a bespoke engine, or at least modify an existing engine so that it is the right shape. I will go into more detail later, but it is really only a few engine cases that have to be modified or made, and most of the internals can be off-the-shelf.

Something like this?
http://i40.tinypic.com/f0qalw.jpg
Mostly off-the-shelf internals, right. But I can assure you, it is not THAT easy to design a new crank-/gearbox-/diff-case around it...

11-08-2011, 02:26 AM

Adambomb,

Yes, Dazz's "Custom Power Train" engine is similar to the UCLan flat-twin. This is my second favourite layout. It packages really well, but is too complicated by one cylinder. http://fsae.com/groupee_common/emoticons/icon_smile.gif Note that in Dazz's car image (at bottom of thread) there is still a triangular void between driver's back and engine (due to large diameter alternator?). I think that one of the important aspects of designing anything is packaging all the things you really need (which is not obvious!) in a neat way. So for FSAE, no empty voids at the CG!

Note that if you drop one of Dazz's cylinders, re-centre the engine with its bigger single cylinder, then you also have a pretty good layout. The single will probably need balance shafts, but you save the complexity of the second cylinder. And there lies the problem with simplificating. It ain't that simple!

~~~~~o0o~~~~~

Jan,

I'm not sure how many cylinders your picture has. If it is a single I might rotate the cylinder about 90-120 degrees clockwise (with exhaust down/back). This tucks the heavy crank under the driver's back, giving nice tight packaging. With regard to designing the "crank-/gearbox-/diff-case" I will cover this in Essay 3 in a couple of weeks. I smell an "opportunity" there... http://fsae.com/groupee_common/emoticons/icon_wink.gif

Z

Jan_Dressler

11-08-2011, 03:34 AM

It is a 4 cyl, based on Honda PC37 internals.. http://fsae.com/groupee_common/emoticons/icon_smile.gif
About rotating: The stock cylinder head is in fact rotated 180° --> exhaust is going up and behind, and not behind the driver's seat and fuel tank.
With regard to designing: I'm really curious... http://fsae.com/groupee_common/emoticons/icon_smile.gif

I needed quite a (very) large amount of time to "re-engineer" all the loads on all the bearings... (AVL EXCITE engine simulation)

Pete G

11-08-2011, 04:11 AM

Time for a bit of show and tell
http://imageshack.us/f/163/transtz.jpg (http://imageshack.us/f/163/transtz.jpg/)

kcapitano

11-08-2011, 10:53 AM

Hmm, Im not at all sure I like where this thread is going. What happened to the philosophy of keep it simple, finish early, drive the wheels off it?

I'm not saying I disagree with Z about engines being the wrong shape, he makes a very valid point (and one I had never thought of before). Most teams, though, struggle to finish endurance as is, without the added complexity of designing an engine block. Not to mention that we haven't yet addressed the manufacturing side of things, I'm thinking of investment casting starting from a rapid prototype, but thats another discussion.

I think that designing your own engine block would be similar to the process Kevin outlined regarding monocoque frames. It can be done quite well, but you would probably need three years to get a product you're happy with.

All this talk has made me curious though. What mass produced engines could be used to solve the packaging issues Z has brought up? And since the engine is "just a necessary lump of ballast" I think we should be more creative in our search. Why not use a lawnmower or snowblower engine?

SmilingThird

11-08-2011, 01:31 PM

Lawnmower...???
Or keep it simple: Use a WR450 backwards, all you need te do is "bolt" on an extra gear to get torque in the right direction. Or you do it in internally by fiddling a bit with the gearbox and while busy remove the 5th gear. I don't know exactly if it's that easy, but I think you get the point. Good thing is that the intake and exhaust "end up" at the right direction as well.

Seeing Jan_Dressler's design and Dazz's (http://fsae.com/eve/forums/a/tpc/f/125607348/m/112101343?r=939101563#939101563) I think they are needlessly complex and go much for a low CG when I think low yaw inertia is more important. These designs look "too much" like other racing cars to me. As Z said, engineers are into "fashion" as well.

And to boldy be ahead of Z's power Essay (what a good name!) I think around 63hp at the wheel should do the job. At DUTRacing we missed a couple of points here and there at acc. and sometimes on track. But in all we did quite well with much less power than other teams.

11-08-2011, 06:09 PM

Ping,

Looks good! More details please http://fsae.com/groupee_common/emoticons/icon_smile.gif. It is similar to the Oxford-Brookes engine in RET, though the O-B engine is a bit more squashed up (diff closer to cylinders). V-twins have two advantages over flat-twins;
1. The crank is simpler in that it only needs a single big-end journal.
2. They sound much better! http://fsae.com/groupee_common/emoticons/icon_biggrin.gif
~~~~~~o0o~~~~~

Kcapitano,

Regarding KISS and finishing endurance, 6 years ago I was encouraging teams to build a "brown go-kart". "Brown" = no frills. "Go-kart" = a single-cylinder engine in a very simple chassis (I was suggesting beam-axles as one option), allowing it to be built quickly, and then lots of (fun http://fsae.com/groupee_common/emoticons/icon_smile.gif ) testing...

Oh, and don't "design" the engine cases, just build them! It's funny, but most of the V8 motorbike engines I have seen over the years (and there are lots of them, mostly made by putting two smallish line-4s on a common bespoke crankcase) were made by young men doing a "mechanic/machinist" type trade course. Maybe it's something to do with "fools rush in where angels, and engineers, fear to tread", but the engines seemed to work... http://fsae.com/groupee_common/emoticons/icon_smile.gif
~~~~~~o0o~~~~~

Smiling,

Find reversed engine discussions on Engine Location (http://fsae.com/eve/forums/a/tpc/f/125607348/m/71310905821?r=71310905821#71310905821) and FASTEST EVER ACCEL TIME 3.97sec! (http://fsae.com/eve/forums/a/tpc/f/125607348/m/61210643621?r=61210643621#61210643621) threads (2005).

63rwhp is plenty. I will explain why in about a week...

Z
(Edit: Wowww... the old fart's figured out how to hyperspace his URLs!)

Ash47

11-08-2011, 06:29 PM

The engine that Ping posted is the V-Twin that University of Auckland is developing. A bit of info about it in this thread (http://fsae.com/eve/forums/a/tpc/f/125607348/m/42420301051?r=36320821051#36320821051).

This is an extension of the teams current V-Single/Transaxle concept in an attempt to design an engine specifically for Formula SAE for the same reasons you have posted. The team had a V-Twin concept semi-running a few years back and I've been redesigning it so it can be tested properly, mated to a transaxle and put in a car (if it gets to that stage).

Just touching on what kcapitano said about manufacturing, a lot of thought went into designing the V-Twin so that it could be manufactured in house with minimal outsourcing. Apart from some CNC patterns for a cast crankcase, all of the machining has been done in house by me. The V-Single crankcases have always been CNC machined from billet and so I have reduced manufacturing costs for the crankcase by 70% for the sake of a week of machining. The engine also uses as many standard Yamaha parts as possible (heads, crankshaft, flywheels, starter, oil pumps etc) which reduces complexity an awful lot and makes it easier to rebuild when you blow it up.

The transaxle in that picture is a concept that is just about to start detailed design so it is likely to change a wee bit. The V-Twin is half complete -> Pictures (https://www.facebook.com/media/set/?set=a.241059805914066.59874.155875141099200&type=3). It should be pretty complete for the FSAE-A comp as a display piece.

Mike Cook

11-08-2011, 08:53 PM

Ash,

That is amazing. Good work. Love to see the finished product. Stick with it and see it through!

Mbirt

11-09-2011, 08:40 AM

I would love to see a team choose the Briggs and Stratton "Blockzilla" architecture for their custom flat- or v-twin. The aftermarket for karting and jr. dragsters is huge and there are several bore/stroke combinations for the same basic architecture to build singles and twins in the 550-610cc range. Using a BMW R45 motorcycle crank for a flat twin, the 2.42" stroke combined with 3.125" bore blockzilla top-ends gives you 608cc. The motor would be air-cooled and significantly less wide than an OHV/OHC motor. The intake and exhaust ports would also face upward so no ducting has to be routed toward the ground.

Ok, so flathead motors aren't sexy. But it could be a highly mass-centralized, lightweight, and technologically managable platform to build a custom engine from.

11-09-2011, 05:14 PM

Ash,

Excellent work. Don't let any problems you might be having with it now worry you in the least. In 10, 20, 50 years time, all you will remember is the great time you had building your very own V-twin!
~~~~~o0o~~~~~

Mbirt,

I'm not familiar with the B&S architecture, but flat-head flat-twins have always struck me as particularly neat packages (there are many examples) - compact, smooth running, simple valve drive. A big aftermarket is also a very strong advantage. Quality parts at reasonable prices off-the-shelf (eg. the sbV8 a-m).

I hope more teams take a close look at this concept, if for no other reason than low cost. (See next Essay for an, ahem, "similar" engine.)

Z

rjwoods77

11-10-2011, 10:22 PM

So if I ever decided to go back to school for a masters degree and get involved in FSAE to ruin my life again http://fsae.com/groupee_common/emoticons/icon_smile.gif what would I do? That is a fun and interesting question that I can answer in this particular post because I fell in love with engine and drivetrain packaging when I did both baja and fsae. Also as Z had mentioned before it all really is an exercise in packaging finesse that separates the adults from the children.

Well pretty much at this point the results of the last 4 years have shown that a single is all you need to win. If you are really power hungry then all you need to do is look at Wattard's research to see a choked restrictor twin is all you really need to absolutely and completely overwhelm an fsae chassis. Therefore it is my contention that anything else above 2 cylinders is masterbation (NOT JUST CARBON!!!) or unwillingness to change from the status quo which has always been my enemy.

Before numbers, diagrams and charts come into play I would eliminate single cylinders from consideration because of the janky sound, the excessive vibration and lack of flexibility in what you can do with them in terms of growing into them as an engine program for the team in terms of learning for post higher education careers as well as manifolding and boosting. In general singles can win the event and probably the best way to go overall but they lack the refinement and flexibility of a twin cylinder and I wouldn't put my time into something that isn't adult league. I shoot Benelli not Remington.

So I would want to use a twin cylinder. As far as bank angle I would go for a flat twin with single crank throws per cylinder ala BMW due to best multi-order balance of all the twins, the sound couldn't be any sweeter and the packaging which I found from many drawings over the years is lowest and most compact than anything out there. A 610cc or less flat twin would be no wider than the template/rules demand the firewall area to be so it is a beautiful transverse rich space to put an engine that is longitudinally stingy. It seems that there really isn't a reason to have a leaned firewall these days so you can put this up directly to you main roll hoop and/or tub. The cylinder width is also of no consequence because where is sits is typically where the angled bars are coming off of the firewall to get to the suspension box. Intake would go vertically up and exhaust vertically down or reverse depending on your manifolding requirements. The rules pretty much dictate a certain amount of space from the ground to where a 90 degree bend would come off the cylinder so exhaust wouldn't hinder the height you could mount the engine as the crank throw with dry sump pan plus chassis rail would equal a height greater than that. Since the engine is mounted right off the firewall it really wouldn't effect aero. I would make the engine direct injected in order to be efficient (BSFC,CR,etc) as possible. This is unrealistic unless you copy/retrofit an OEM system. Guess what? There are a number of small four cylinder engines out there that meet the bill in either the N/A or boosted application when you cut them in half from a 4 cylinder to a 2 cylinder. There are even a couple 3 cylinder ones you could use to if you decide to go on the small end of capacity. Pick you direction and copy/retrofit with OEM parts to drastically cut down on the work. See Audi 1.4L TFSI or 1.3L Mazda Skyactive or 1.2L GDI Kia Rio. Use the pistons and make the stroke accordingly. If you want custom pistons to match then laser scan and call Wiseco.

I will have to admit something folks. I love cvt's. I know they are gooey black magic but in reality they are excellent devices for fsae that have been under utilized. I watched some F500 compete at a recent RIT SCCA event and their usefulness is undeniable. The fun part is how this engine drivetrain gets packaged with the engine. My engine would have a vertical crank instead of a longitudinal. I would mount the primary cvt on top of the engine in the manor Porsche did with their cooling fans. I would then run the belt toward the back of the car where the secondary would be sitting over the rear suspension box. I would then take an atv diff that is popular to use for it cam and pawl and or whatever diff is fancy now. The secondary clutch would plug into the diff housing vertically. I would bolt the diff housing to the engine block and use simple spacer such as the camber adjusters for late model DIRT cars to easily control belt tension so that the diff housing wouldn't even be bolted to the chassis. The entire transmission would be sitting above the engine with uber easy access to modify and tune while being out of the way of everything. I would use a Bergman 650 cvt since it has a servo controller on it that allows you to operate the clutch in full auto or programmable shift points as it has on the bike. In this way you can have a fully auto tranny or a electronic quick shift tranny that uses the belt as a cush drive for beautifully simple and non jerky shifting as it works on the Bergman. Manifolding is up to the chassis and aero guys.

The entire engine would fit longitudinally from main roll hoop centerline to diff housing output shaft centerline(rear axle centerline) in 18 inches. You pay a little bit on cg for the cvt being up a bit but it is way better than almost every other option. The entire engine and drivetrain module would fit almost in a perfect box as Z has mentioned previously that is highly desirable. Past that I would convince the team to use his ever infamous z bar suspension to have soft modes and then mount the aero directly to the unsprung mass. What in the name of Z? I just finished my beer and time for bed. I missed some stuff but you get the idea. Besides...first post in like 3 years. Enjoy.

P.S. Hey Z. I want to talk to you possibly by webcam about using your z bar in an Ariel Atom type car with a 4 rotor wankel engine and awd.

rjwoods77

11-11-2011, 10:13 AM

Originally posted by Z:
Ping,

Looks good! More details please http://fsae.com/groupee_common/emoticons/icon_smile.gif. It is similar to the Oxford-Brookes engine in RET, though the O-B engine is a bit more squashed up (diff closer to cylinders). V-twins have two advantages over flat-twins;
1. The crank is simpler in that it only needs a single big-end journal.
2. They sound much better! http://fsae.com/groupee_common/emoticons/icon_biggrin.gif
~~~~~~o0o~~~~~

Kcapitano,

Regarding KISS and finishing endurance, 6 years ago I was encouraging teams to build a "brown go-kart". "Brown" = no frills. "Go-kart" = a single-cylinder engine in a very simple chassis (I was suggesting beam-axles as one option), allowing it to be built quickly, and then lots of (fun http://fsae.com/groupee_common/emoticons/icon_smile.gif ) testing...

Oh, and don't "design" the engine cases, just build them! It's funny, but most of the V8 motorbike engines I have seen over the years (and there are lots of them, mostly made by putting two smallish line-4s on a common bespoke crankcase) were made by young men doing a "mechanic/machinist" type trade course. Maybe it's something to do with "fools rush in where angels, and engineers, fear to tread", but the engines seemed to work... http://fsae.com/groupee_common/emoticons/icon_smile.gif
~~~~~~o0o~~~~~

Smiling,

Find reversed engine discussions on Engine Location (http://fsae.com/eve/forums/a/tpc/f/125607348/m/71310905821?r=71310905821#71310905821) and FASTEST EVER ACCEL TIME 3.97sec! (http://fsae.com/eve/forums/a/tpc/f/125607348/m/61210643621?r=61210643621#61210643621) threads (2005).

63rwhp is plenty. I will explain why in about a week...

Z
(Edit: Wowww... the old fart's figured out how to hyperspace his URLs!)

90 degree v-twins do sound cool, especially lawnmower engines, but after seeing vintage BMW flat twin bike run around I would have to disagree. One down side to non 180 degree crank twins is the uneven firing. With the restrictor it makes analysis odd and I think might other physical effects as far as the incoming charges being different to each bank. Our engine used to run one bank hotter than the other which I always found odd.

http://www.youtube.com/watch?v=sqztOLYcwek

Adambomb

11-12-2011, 01:55 AM

Originally posted by rjwoods77:
90 degree v-twins do sound cool, especially lawnmower engines, but after seeing vintage BMW flat twin bike run around I would have to disagree. One down side to non 180 degree crank twins is the uneven firing. With the restrictor it makes analysis odd and I think might other physical effects as far as the incoming charges being different to each bank. Our engine used to run one bank hotter than the other which I always found odd.

Yep, I like the sound of a nice high-revving twin. Or for that matter an odd-fire four. The odd-fire four brings the same questions to light. The Yamaha R1 makes a good opener for that discussion. They tout it as if it was some "revolutionary technology," when in fact it is the exact same configuration as my '88 Ninja 600, as well as many older rockets.

Someone who knows better feel free to correct me on this, as most of the following is more or less based on observation: Odd-fire fours (firing at crank angles of 0-90-360-450) are more inherently balanced than their even-fire brethren, lacking the second-order couple that necessitates a balance shaft spinning at 1/2 speed. Back in the late '70s-80s, when motorcycle engines were just breaking the 10,000 rpm barrier, this better balance was "the trick" to get them to live at this rpm. However, their uneven intake and exhaust pulses made for less effective pulse charging and scavenging. In the '90s everyone figured out that you could make more power with even-fire, and got the balance issues worked out, and even-fire 4s were king. But then a couple years ago the folks at Yamaha remembered how sweet the odd-fire engines sounded, wrote off some excuse (or possibly quantified?) a decision to switch back to odd-fire (even if for marketing only...not a bad idea if you're in the business of SELLING bikes!), and now you have the "revolutionary" odd-fire 4.

There's just something magical sounding about a 90 (or even 72) deg. firing spacing. My old Ninja sounds like a cross between a Ducati and Ferrari, and the R1s are 3 times as mean. But there's no doubt an odd-fire twin creates more uneven pulses in the intake, which as my first guess would be not quite as bad as a single, but not as good as an even-fire would. So basically the same factors that made the even-fire 4s more effective in rockets are doubly important with a restrictor. But again, it's all a compromise. And in the end all you really need is a necessary lump to get the car around the track. If it sounds good that can get you more marketing points, I know we need help at that anyway. http://fsae.com/groupee_common/emoticons/icon_smile.gif I really like how that UB car sounds.

11-12-2011, 03:18 AM

Hello Rob!

Welcome back. I'm only here because somebody lent me an interweb box thingy. It operates over the airwaves, so very slow, but ok for reading these posts. PM me and I'll give you my email address.
~~~~~o0o~~~~~

Adambomb,

Just briefly, even-fire fours have a second order "shake" (up-down) that needs two balance shafts rotating at twice crank speed (20,000+rpm). Odd-fire fours ("90deg. crank", like most V8s) have a <STRIKE>second order</STRIKE> (Edit) varying magnitude and direction primary order "couple" unbalance, which is slightly less annoying (End Edit, corrections welcome). I think a lot of the "marketing" here has to do with MotoGP, etc., where they have been switching back and forth between even and odd fire for decades. There used to be a lot of talk about "big-bang" vs "screamers" with regard to tyre grip and controlability. Nowadays the talk is more in terms of "gas pressure torque" vs "inertia torque". I have yet to hear a really clear, technical comparison between the two.

Z

PS. My comment re: "better sounding Vs" was tongue-in-cheek (heart not head). http://fsae.com/groupee_common/emoticons/icon_smile.gif

11-12-2011, 03:35 AM

Essay 2. How Much POWER is Enough?
==================================

The answer to this question is found down memory lane...

A long, long time ago, in the late 1960s, Ford were dominating Le Mans with their GT40s. Up until then Porsche had been successful in the smaller classes, but now they wanted outright victory. So they built a MONSTER! Yes, boys and girls, they built one of the most fearsome racecars ever to turn a wheel, the PORSCHE Type 917 !!! This was quite a small car, 690kg with a wheelbase of only 2.3 metres, but it was powered by a 4.5 litre air-cooled flat-twelve. When first tested the engine gave 540hp, but more was to come...

The 917 was first shown at the March 1969 Geneva Motor Show, so only a short development period before the June '69 Le Mans. The drivers soon found out just how short was that development. The aerodynamics were abominable, with the low drag "long-tail" generating rear lift! But, it WAS fast. Sadly, one 917 was involved in a fatal off on the very first lap. The others led for 20 hours before succumbing to gremlins. In 1970 the 917s were back and won Le Mans and almost every other long distance race on offer. Likewise in 1971, when a 917 set the outright Le Mans lap record that still stands today. And so, as so often happens in these situations, they were banned. As good a compliment as you can get, if you see the glass half-full. http://fsae.com/groupee_common/emoticons/icon_smile.gif

What was Porsche to do? Well, they picked up their cars and went to play in North America, specifically the Canadian-American Challenge Cup, or Can-Am. At this stage the regular Can-Am players, mainly Chaparral, McLaren, and Lola, had a very successful decade long arm's race behind them. The engines had grown from stock-block 5 litre V8s, to bespoke all-alloy 8 litre (500ci) fuel-injected V8s making around 750hp.

Meanwhile, Porsche's 917 had grown to 5.4 litres. But was this enough to run with the big boys? Porsche figured not, so they decided to try "turbo-charging", a novel concept in motorsport at the time. To ease their transition into Can-Am, Porsche had signed American Mark Donohue. Along with being lead driver, Donohue was also a qualified engineer and he had a big hand in the development of the Can-Am version of the 917. After totally dominating Can-Am in 1972 and 1973, the 917 was effectively banned for 1974. But it was too late, and the 917 is often called "the car that killed Can-Am".

After the 1973 season Donahue was interviewed by Autocar magazine. Below are some selected words from that article.

"1100bhp, 240mph - Porsche 917/30." (Autocar, 11 May 1974)
==================================
"... With the turbochargers set to deliver 1.3atm boost, the 5.4 litre engine gives about 1,100bhp, ... Increasing the power further is as simple as turning the screw on the blow-off valve ... several of the Porsches ... had devices to allow the driver to increase boost from the cockpit. "I used mine only once, at the end of a race," says Donohue. It is estimated that the increased boost - to 1.7atm - gave more than 1,200bhp. (At 2.2atm on the test bed a figure of 1,560bhp has been recorded!)"

[Similar 1500+bhp figures for "qualifying" are quoted in other sources.]

"... Is this really going too far? Have these cars got too much power, more than they can ever use? Donahue answers emphatically: "Too much power is defined as when at the end of the straight in top gear the wheels are still spinning, ... We estimated how much power was needed to do that ... 2,400bhp ... Can you imagine what a thrill that would be? I'm a horsepower freak.""

~~~~~o0o~~~~~

Apologies for the rambling introduction, but I wanted to set the scene for what follows (and also to remind you how interesting motorsport used to be http://fsae.com/groupee_common/emoticons/icon_smile.gif ).

What has the 1,000++hp 917 got to do with FSAE? Well, the really interesting thing is, of all the classes of circuit racing I know, autocross and FSAE come closest to Donahue's definition of "too much power"!

How so? The rule of thumb for conventional IC engines breathing through a restrictor is, in round numbers, a maximum of 30kW or 40hp per square centimetre of restrictor area. (This is my estimate based on observation of all sorts of well developed restricted engines.) So, given that pi=3 and radius=1cm, a fully developed FSAE engine will peak at 90kW (120hp) at the crank. Still working in round numbers, about 1/4 to 1/3 of this power is lost on its way to the ground. So let's say that maximum "drawbar power" is approximately 60kW (80hp). This power definition is used with tractors and is equal to drawbar force x velocity (ie. P=F.V).

In FSAE terms, "at the end of the straight in top gear" is about 30m/s or 108kph (~67mph). The maximum drawbar force, or "thrust", that a maximum power FSAE engine can exert at this speed is F=P/V or 60,000W/30m/s = 2,000N, or 200kg. A lightweight FSAE car of 200kg total weight, with 2/3 rear dynamic weight (67%R), and tyre coefficient of 3/2 (Cf=1.5), with the rear wheels just spinning has thrust of 200x(2/3)x(3/2) = 200kg (which, of course, gives acceleration of 1G).

So with 60kW at the rear wheels (80rwhp) this 200kg car has "too much power" by Donohue's definition! Or at least "enough" power. Admittedly, this is a very light car, maybe 140kg + small driver, and it has a "maximum power" engine (maybe 1/12 of the 917 engine?). But my point is that FSAE is very close to Donohue's Holy Grail.

What if you only have 30rwkW (40rwhp)? Well, you are half way to heaven, and in a similar position to Donohue when he only had 1,200hp, and wanted 2,400hp! 45rwkW (60rwhp)? You are knocking on the door to Nirvana, and so on... But, don't forget that you need a lightweight car to have this much fun. http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

What if you are a poor team, and you are worried about all those super-rich teams, with their mega-powerful engines in their hyper-light cars? Again, you really shouldn't worry. The "wheels still spinning at the end of the straight" sets an upper limit to any advantage that can be gained by increasing power or adding lightness. Once at that limit the rich teams can spend as much as they like on power and lightness, but they won't go any faster.

But it gets even better! According to many posts here, FSAE cars spend less than 20% of Autocross or Endurance at full-throttle, ie. "trying to spin their wheels". Also, average speed is 40-50kph, which implies that significant time is spent at less than about 40kph, obviously in the corners. Put simply, these events are won in the corners. Raise your corner speed from, say, 39kph to 49kph, and you only have to go a little faster down the straights to get your average up to, say, 51kph, and be a winner.

Even with huge slip-angle and aero drag, a rough calculation suggests a lightweight FSAE car needs only about 15rwkW (20rwhp) to go fast enough through the corners to win. However, the engine has to deliver this power 100% of the time, so make sure it can do so reliably.

The bottom line is that YOU DO NOT NEED MUCH POWER to do well in FSAE. If you happen to have a good engine and a light car you can have more fun than Donohue and his 1,200hp Porsche.http://fsae.com/groupee_common/emoticons/icon_biggrin.gif But if you want to win you should concentrate on going faster through the corners. And the way to do that was known back in the 1960's, although Porsche didn't fully appreciate it in 1969. (Hint: It is a topic for another thread, but the answer is blowing in the wind, and it works better with a light car. http://fsae.com/groupee_common/emoticons/icon_wink.gif )

More later... (namely: What Type of Drivetrain?)

Z

Mike Cook

11-14-2011, 09:15 AM

But Z...............

Last time I checked there were no 140kg cars making 80hp.

Lets be a little more realistic,

lets say my car
weighs 600lb w driver
400lb DF@ 60
133lb drag @ 60

@ 60 to spin my tires, I need to produce
dynamic rear weight*1.5 =
(600*.6 + 600*1*12/72)*1.5 = 360+100*1.5 = 460*1.5+133 = 690 lb thrust

P = F*V
V = 88ft/sec = 5280 ft/min
690lb*5280ft/min = 110hp

And that is at 60mph. The corner exit speed should be higher for this car than your example, but the aero drag will reduce its top speed.

Tickers

11-14-2011, 10:32 AM

I'd say somewhere between the two is more realistic. There probably aren't many FSAE cars making ~200kg of downforce, given how few run wings.

Besides, he was making a point that needs to be made. I think the most important one is how little time FSAE cars spend at full throttle. The constant search for power is completely pointless in this game, when you're never putting it down.

Get a drivable engine with a bit of power in a car with a decent setup and you're sorted.

Big Bird

11-14-2011, 10:55 AM

When we took our car to Detroit for the first time in 2005, Rotor was lapping as quick as Cornell (overtook them at one stage), in a car that I'm told was running at around 35kW max. That's what I've been told anyway, I was having a hiatus from RMIT that year.

When you think of what pursuit of engine performance does to mass, fuel usage, cost, reliability....

11-14-2011, 06:41 PM

Originally posted by Mike Cook:
Last time I checked there were no 140kg cars making 80hp.
Mike, that would be my LONG TERM goal. First year, start with a VERY simple (indeed crude http://fsae.com/groupee_common/emoticons/icon_wink.gif ) and lightweight car with a single making maybe 50hp at the crank. Second year, fit efficient aero direct to the wheels (nothing like normal formula cars, which are grossly inefficient thanks to 40yrs of crippling rules). Third year, and just for fun http://fsae.com/groupee_common/emoticons/icon_biggrin.gif , ask the engine guys to "look at that old 917 engine that had individual air-cooled cylinders of 450cc, making 125hp each...".

Now, as for your calcs, you are really making me work hard here ("hmmmmm, I wonder if those are slugs???" http://fsae.com/groupee_common/emoticons/icon_confused.gif ).

Lets say your car
weighs 2700N w driver (~270kg)
1800N DF(downforce?)@ 27m/s (~60mph)
600N drag @ 27m/s

@ 27m/s to spin your t<STRIKE>y</STRIKE>ires (at end of straight), you need to produce
dynamic rear weight*1.5(Cf) =
(2700*.75(R%, incl wt trnsfr from accel) + 1800N*0.6(RDF%) + 600N(drag vector)*12(drag height)/72(wb))*1.5 = (2025+1080+100)*1.5 = 3205*1.5(*only, see note) = 4808N thrust

P = F*V
4808N*27m/s = 130kW *1.33 = 173rwhp!

So, not possible to spins wheels because of restrictor + too heavy car http://fsae.com/groupee_common/emoticons/icon_frown.gif + good downforce! http://fsae.com/groupee_common/emoticons/icon_smile.gif

(*Note: You don't have to add the aero drag force to the tyre thrust ("460*1.5+133"). The engine + tyres produce what thrust they can. Some of this overcomes aero drag, then any excess overcomes inertia - ie. is available for acceleration. So low aero drag cars accelerate out of high speed corners faster than high drag cars, all other things equal.)

Corrections welcome...

Z

Mike Cook

11-14-2011, 06:52 PM

I now understand how they crashed the space shuttle. Too many conversions.

I actually didn't use the 133, because 460*1.5=690, I corrected the post earlier but forgot to delete it.

I think we are both saying the same things. I just wanted to show that with other variables, you can't nearly spin your tires at the end of the straight... http://fsae.com/groupee_common/emoticons/icon_smile.gif

(*Note: You don't have to add the aero drag force to the tyre thrust ("460*1.5+133"). The engine + tyres produce what thrust they are capable of. Some of this overcomes aero drag, then any excess overcomes inertia - ie. is available for acceleration. So low aero drag cars accelerate out of high speed corners faster than high drag cars.)

Corrections welcome...

Z

11-14-2011, 07:11 PM

Originally posted by Mike Cook:
I think we are both saying the same things... you can't nearly spin your tires at the end of the straight... http://fsae.com/groupee_common/emoticons/icon_smile.gif

Agreed. Not with aero.

But after the comp, throw the aero stuff away, fit hard compound (low Cf) tyres, and yeeehaaaahhhh!!! http://fsae.com/groupee_common/emoticons/icon_biggrin.gif
(Edit: Sorry people, that's a stupid comment! Typical juvenile thinking that stops so many teams from doing well... http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif )

(Oops, I missed that 460*1.5=690...)

Z

Spetsnazos

11-14-2011, 10:23 PM

Riveting tales indeed guys.

Mbirt

11-15-2011, 08:53 AM

Originally posted by Mike Cook:

Last time I checked there were no 140kg cars making 80hp.
The closest I can think of is the Wisconsin 2011 car which was lighter than its 325 lb MIS weight in Cali and supposedly makes 85 hp at the sprocket.

11-15-2011, 04:38 PM

Mbirt, I had a quick look at the B&S parts. If building a bespoke engine I would definitely use a larger crank, at least 1.5" or 40mm diameter journals, with pressure oil feed. The 1" splash fed big-end might hold up for a short drag run, but I would want more reliability for lots of testing, Endurance, etc,.

Z

rjwoods77

11-16-2011, 01:38 PM

Originally posted by Mbirt:
I would love to see a team choose the Briggs and Stratton "Blockzilla" architecture for their custom flat- or v-twin. The aftermarket for karting and jr. dragsters is huge and there are several bore/stroke combinations for the same basic architecture to build singles and twins in the 550-610cc range. Using a BMW R45 motorcycle crank for a flat twin, the 2.42" stroke combined with 3.125" bore blockzilla top-ends gives you 608cc. The motor would be air-cooled and significantly less wide than an OHV/OHC motor. The intake and exhaust ports would also face upward so no ducting has to be routed toward the ground.

Ok, so flathead motors aren't sexy. But it could be a highly mass-centralized, lightweight, and technologically managable platform to build a custom engine from.

Mbirt,

If you didn't notice that is a B&S V Twin that was used in our formula car that I linked in the video.

Mbirt

11-17-2011, 07:55 AM

Z,

Splash lubrication is one of the elegantly simple elements of the design I would like to keep if my team were designing its own engine. Many modified 4-stroke racing karts with splash lubrication see more hours of runtime in a weekend than an FSAE car could see in an entire season. The con-rod dipper or splashing gear works with thinner oils that are formulated to lubricate effectively in a "fogging" manner. The Raptor engine has a deep history in karting and the Blockzilla jr. dragster engine is functionally similar, but with more choices available for displacement.

Rob,

Oh yes. I've known about UB and UM-Dearborn's success with the B&S v-twin since I got started in FSAE in 2008. I particularly love the sound of the UB car in the VIR acceleration event clip.

The flathead Briggs-based v-twin and flat twin was just a possible solution I stumbled upon for the port placement/redundant timing chain problem Auckland has run into. The simplicity of air cooling and splash (fogging) lubrication and mass-centralization are icing on the cake.

With this said, we're OBJECTIVELY choosing an engine here. A 65-70 lb 450cc-class single cylinder engine with an integrated transmission is still my choice to power an FSAE car--despite the academic and aural gratification a custom multi-cylinder engine may bring. We'll see how the 3 or more custom twins coming from various European and Australian teams perform in the coming years.

11-17-2011, 08:36 PM

Originally posted by Mbirt:
Splash lubrication is one of the elegantly simple elements of the design I would like to keep...
Mbirt, by all means, if you can make it work, then great. My main concern was with the 1" big-end journals on the (already rather flexible) S shaped flat-twin crank. But perhaps with extra outboard roller bearings to keep everything lined up???

As you know, I love simple, even to the point of "crudity". Ah, the legendary Lanz Bulldog ... sigh ... http://fsae.com/groupee_common/emoticons/icon_wink.gif

My approach to "designing" something like this would be to buy the aftermarket parts, make whatever extra stuff is needed, then put it on the dyno until it breaks. Then strengthen, and repeat. Then add S/C, and repeat...

I'd love to see someone successful with this.

Z

11-21-2011, 11:12 PM

Essay 3. What Type of Drivetrain?
=================================

A big attraction of motorbike engines is that they come with built-in transmissions. Buy the cylinders and you get a clutch and sequential gearbox free. And the output sprocket is in a convenient position to connect to the usual rear drive differential (ignoring for a moment that this pushes the driver too far forward).

But is this the, ahem, "optimal" drivetrain layout? Should not an optimal drivetrain send exactly the right amount of thrust to ALL of the wheels? Well, putting it briefly, All-Wheel-Drive is an extremely difficult thing to do properly, and it only gives small gains at considerable costs.

Doing AWD properly would probably involve an Infinitely Variable Transmission for each wheel, together with a clever control system. Even “just” using N-1 active diffs for N wheels has all sorts of disadvantages. Perhaps the main problem with driving the front wheels is that if they develop too much forward thrust, then their lateral thrust, and hence ability to steer the car, suffers. For cars that MUST be front heavy, such as WRCs that must be developed from front-drive hatchbacks (Rules), it makes sense to drive all the wheels. With freer regulations, like FSAE, just rear-wheel drive is enough. Top fuel dragsters don't seem to suffer from lack of front-drive.

Judging by the number of threads here on differentials, it seems that even figuring out how to send the drive to just the two rear wheels is not a trivial matter. Open diff? Spool?? Something in between??? In what follows I will take it as given that the car has rear-drive only, and will leave the differential for another thread.

So what type of drivetrain should go between the engine and diff? The previous Essay 2 suggests the obvious answer. And that is ( ... drum roll ... ) just a clutch and single step down ratio! What the ...!!! Or, why?

An IC engine is, to a first approximation, a constant torque device. That is, it produces constant torque throughout its working rev range, with power rising linearly (Power = Tconstant*Revs). By comparison, an electric motor is more like a constant power device, with torque dropping inversely with revs (Torque = Pconstant/Revs). Both have a maximum speed limit set by various factors, breathing and structural strength in the case of the IC engine.

One little problem with the IC engine is that its torque drops off below a certain speed set by the "tune" of its cam and intake/exhaust lengths. (Likewise, an electric motor doesn't have infinite torque at stall, but at least it can "self start".) The not so simple, but currently well developed solution to this problem is the friction clutch. Crude, but it works. A better solution is an IVT, but probably too much development for a low budget team (if anyone is interested in IVTs, use "Find").

Now, given that our hypothetical, lightweight, maximum power car of Essay 2 could be "spinning its wheels at the end of the straight in top gear", it follows from its constant torque output that it could remain in top gear and still spin its wheels anywhere on the track! Well, at least hypothetically...

So, would an engine, beefy clutch, then single stage chain drive (or fixed pair of gears) to the rear axle be feasible? If done right, then most definitely "Yes!".

Keep in mind that if the overall ratio is set just below "spinning the wheels", then this would be a very easy car to drive. (Remember that maximum grip is just before the tyres "break free", ie. at 10-30% slip-ratio.) In tightening or opening radius turns you modulate the throttle as required. Turn onto the straight, at any speed, and floor it. Maximum acceleration with no wheel spin. No clutching, shifting, and jerking forwards and back. Not even any "no-lift paddling" with its inevitable change in wheel thrust.

The important point is, if you can nearly spin the wheels in top gear, then there is really no need for a lower gear. All that a lower gear does is allow you to, perhaps inadvertently, "smoke the tyres", and then possibly spin the whole car just when you want to be going straight.

Certainly, there are many little details to resolve, like having a "Neutral", but I'll address those next Essay. To repeat the key point of the last Essay, if the car can go fast through the corners, then it really doesn't have to go much faster down the straights. That is, if the car can maintain roughly 50kph (30mph) everywhere, give or take a bit, then it will win. And that only requires one gear.

But I am sure that many of you are now thinking "Z's lost it again! Real circuit racing with only one gear? Impossible! And don't mention go-karts... Or speedway... They're not, err, Formula! ".

So I will leave it to someone else to convince you. The following is from one of Forbes Aird's articles. I strongly recommend reading the whole article, if for no other reason than Forbes' very appealing writing style.
~~~~~o0o~~~~~

"Ratiocination" (Racecar Engineering, Nov 2010, V20N11)
===========
(Forbes starts with steam engines (no gears), and then describes the various perils and pitfalls of the "change speed gear box". Then follows this section on Michael Schumacher in his Benetton Ford at the 1994 Spanish GP.)

"On lap 21, Schumacher's 'change speed' was visited by a glitch ... stuck terminally in the fifth of its six speeds. After a futile swap of the steering wheel ... a shove by the pit crew worthy of an Olympic bobsled team... Lap times sagged from around 1:26.8 to 1:31.8 ... as the Benetton screamed and stuttered along on the rev limiter at 16,000rpm on the long straights, and slugged around the twisty bits at well below idle speed."
...
"Schumacher persevered."
...
"... race commentator Jonathon Palmer found it very hard to believe: 'I do find this very hard to believe,' he said. ... By lap 30, Schumacher was back into the 1:27s. 'It is inconceivable...' protested Palmer. On lap 38 Schumacher turned a 1:26.3, to which Palmer responded, 'I would go so far as to say it is actually impossible.' Schumacher completed 42 laps thus handicapped, and finished second."
...
"... the absence of 5/6ths of the gearbox cost an average of barely two seconds a lap. Imagine if he had had two speeds..."
~~~~~o0o~~~~~

And that was in Formula One!

So maybe two gears ... at most... http://fsae.com/groupee_common/emoticons/icon_smile.gif

More later, namely "Essay 4. Putting it All Together"

Z

Kevin Hayward

11-22-2011, 12:26 AM

Z,

I would argue that with a standard motorcylce engine you buy the transmission and get the cylinders for free. The transmission makes up for a large number of parts and total weight and doesn't add a lot. Many cars in FSAE have done very well running the endurance in one gear. Even with heavy cars.

As for neutral - the shifting system ECU (Edith Cowan Univeristy) uses is a very simple CO2 system. It has no ability to get into neutral by pressing buttons. During the event the car is started by holding the clutch in. There is some clutch drag to overcome, but I think anyone who is designing their battery and starting system on the limit is asking for trouble in this comp.

I would definitely agree that motorcycle engines as they are not ideal for FSAE. However you bolt in a CBR and it just works. It will also have enough performance that the acceleration performance of the car is not as sensitive to weight.

As for the cornering it is important to note that in practice the grip of FSAE tyres are not very load dependent. They are definitely temperature and camber dependent. It ends up meaning that a light car is often not at too much of a cornering advantage in the endurance event, and possibly at a slight disadvantage in the skidpan.

All that being said if I were to build an engine for FSAE it would likely be something similar to what you are suggesting.

Kev

Boffin

11-22-2011, 03:28 AM

Z, I haven't read all of this thread yet (will over the next few days) but to add fuel to your fire, we're running a CBR600RR with a final drive ratio of 15/43, thus 2.87.

Figure out how many gears this get's us using (i'll give you a hint, it's one of the numbers in the numerical ratio), and where more importantly, yet look at our lap times compared to Monash.

11-22-2011, 04:21 AM

Kevin,

Good to hear that "many" teams manage with just one gear (at least in Endurance). I was expecting more flak on that, though early days yet...

The funny thing is that the "sequential 'box" is very often used as the justification for using an off-the-shelf bike engine. But ultimately it pushes the driver forward, increases yaw inertia, and spoils the whole package. Scrap the 'box, rearrange what's left, and the whole package works better (IMO).

Regarding lightweight cars, I see two main advantages:

1. Lighter = less to build, so cheaper and finished earlier.

Note this does NOT work if lighter = carbon-fibre and titanium everything. It DOES work if lighter = no 6-speed 'box, no double-wishbones, no pushrods and rockers, no ARBs, no R&P plus bevel-gearbox (other thread), etc.

2. Aero! A given amount of downforce gives more corner speed to a light car than a heavy car (eg. 100kg of downforce on 200kg car + driver gives +22% corner speed, but only +15% corner speed on 300kg car, roughly).
~~~~~o0o~~~~~

Boffin,

How heavy is your car? Do you have aero?

Z

Boffin

11-22-2011, 04:52 AM

240/250kg, no aero. 90ish hp at the wheels, and 70+ nm's

And I'll be the first one to admit that it's over powered

CameronBeaton

11-22-2011, 04:57 AM

I generally agree with you on most points but this statement.

Originally posted by Z:
Top fuel dragsters don't seem to suffer from lack of front-drive.

I think the drag test is the one place a 4-wheel drive system would benifit with traction from standstill. Top fuel dragsters can get away with 2-wheel drive because the exhaust produce a surprising amount of downforce that gives them the traction they need to put the power down.

Kevin Hayward

11-22-2011, 05:22 AM

Z,

The recent rule changes to aero have been a real game changer. It was borderline as to whether the extra effort was worth the lap times on the larger CBR cars with the old rules. Now the smaller engined cars are getting more power and there is a dramatic increase in the aero you can produce.

Monash should be very interesting to watch this year. I think the changes to the aero rules may have more long term influence on powertrain choice than the increase in the points allocated to endurance.

Kev

Mbirt

11-22-2011, 02:08 PM

Originally posted by Z:
So, would an engine, beefy clutch, then single stage chain drive (or fixed pair of gears) to the rear axle be feasible? If done right, then most definitely "Yes!". I envision this working with the Jawa 500cc "laydown" flattrack racing motorcycle engine, the crankcase close to and almost below the differential, the cylinder pointing toward the firewall. The low motor height would allow the drivers' torso to reside mostly above the cylinder. A sprag clutch for electric start could be integrated into the centrifugal clutch solution.

I must credit Rob Woods for bringing up the Jawa first. It weighs only 3 lb less than a WR450, but the simplicity gains with the centrifugal-clutch single-speed drive and air cooling make it attractive.

11-22-2011, 05:29 PM

Mbirt,

Yes, and that could be done with a single stage gear drive integrated in a common crankcase and diff housing. Simple, rugged, compact, etc...

Or, as a preview of Essay 4;

With the heavy crankcase pushed up under the driver's back (closer to the CG), cylinder head just under the rear axle, and a longer chain drive back to the diff. This gives simple crankcase build (using any off-the-shelf head and barrel), and standard tech FSAE final drive.

If using a more upright cylinder off a standard bike, for less reworking, then as above but with the cylinder at 45 degrees and the head just above the rear axle.

Or, with the cylinder again laid down but lateral, and with the longitudinal crank driving through clutch direct to bevel drive diff. In side view the crank might slope down-to-front, because engine is lower than rear axle. This is super compact, like a log that the driver reclines on. But getting the right overall gear ratio might be hard (ie. would have to swap crown and pinion).

So, to allow quick and easy overall ratio changes, as above but with the crank driving backwards under the rear axle, then chain drive sideways to a bevel drive diff (with rearward pinion) mounted just behind the cylinder head. The chain and sprockets are super accessible, and since lightweight, their "rear overhang" would not be too bad for mass distribution.

Or, as above but with Rob Woods' "gooey black magic" rubber band CVT replacing the chain drive (see Rob's earlier suggestion).

So, lots of simple, compact, low CG, low yaw MoI packages are possible, and not too many bespoke parts have to be made...

Z

Jay Lawrence

11-22-2011, 08:25 PM

UoW ran a single gear (on purpose) in 2008. The experience was not entirely beneficial... basically it meant that you either had to have adaptive clutch control (didn't crack that one and non-adaptive didn't work out with the variable nature of the clutch system) or accepted that to get a reasonable top speed, your minimum speed was governed by your idle. Our top speed was about 98km/h (hit limiter during accel.) and our idle (to keep the turbo happy) was not constant, making 'idling around' not very pleasant. The 'neutral' was simply engagement of the clutch. Because our clutch was extra beefy to handle our torque output, this meant that there was a reasonable amount of drag all the time. We did, however, manage to save a large amount of weight from the 'ballast' section of the car... (and noticed some nice power increases due to the reduced rotational inertia).

We had about 100Nm max. engine torque at our disposal, which made the car quite ballistic between its' speed limits. However it was not very efficient at comp average speeds because of said gearing and the throttle position required to do managable speeds.

The following year the car had 3 speeds and was much easier to drive whilst still maintaining the 100Nm (spread of something like 80% between 6000 and 11000rpm). Plus we had a proper neutral back, which was nice.

So basically... more work required to make it feasible on a standard engine. I would imagine that finding the right balance with a single or other less powerful engine would be more difficult, but I guess then you can consider the CVT option perhaps.

Oh and despite our selling of the single gear concept (in more glowing fashion than i have put above) to the judges, they couldn't accept it. We got the feeling that they thought 'it just won't work' and I imagine the same barriers will be met no matter how good the concept.

rjwoods77

11-22-2011, 08:51 PM

Couple statements first. The general theme of this discussion has been packaging the best drivetrain "box" we can manage. The best "box" being determined by least waste of space, 7:1 or lower weight to power ratio, lowest possible cg, tractable transmission setup (i.e. easy to drive), and what I will refer to as oops management. Oops management being we didn't get the manifolds,tuning,ratios,etc right which in other words design some flexibility into your "box" because it is inevitable that you didn't account for something correctly and you don't want to bomb your whole season on getting a couple things wrong that will sink you.

A typical (i.e Honda 450) single cylinder has proven to be capable of winning the competition but it hasn't been the best setup it could be due to lack of options in layouts to achieve the best "box" possible. It has been agreed in this discussion that if you could get a PTO output single and build your own transmission setup after it then it would allow you packaging options to achieve the best box.

While I agree that Z's simplistic clutched single drive chain ala Jawa speedway bike http://www.youtube.com/watch?v=UYoRDFBD_Sc (which by the way is the smoothest and best sounding single I have ever heard in person over any thumper by far) is an interesting concept but it contains a lot of oops factor. Drivers are far from perfect and "getting off the pipe" (2 stroke term but same effect no matter what engine) because of a shitty driving is very likely due to the amature nature of the driving populous of FSAE. There is what I consider a substantial inflexibility due to picking a single which is already down on power and then to add on a centrifugal clutch direct drive to the mix. Typical FSAE cars need to go around approx 60mph on the high side of redline gearing in order to have meat in the usable driving region 20mph to 40mph.60mph with 18 inch OD tires and 20 inch OD tires, which is approx 1120rpm or 1000rpm at the rear axle respectively, with a driect drive single topping out at 9000rpm will reguire a huge final drive of 8:1 and 9:1 respectively. That doesn't fit the nice packaging requirement in the least. Anything other than single speed direct drive (i.e. low/hi box) defeats the concept and leads back to a transmission option.

As far as transmission options are concerned you can go with a 2 or 3 speed gearbox with some sort of final drive or go with the black magic gooey noodle CVT with final drive which is the best option to meet the criteria explained above and here is why.

1) It is the supreme in tractable transmission setup (i.e easy to drive and easy to recover from an f-up and much less parts and cockpit hassle). After watching Dearborn dust most of the field in the autocross with a weight to power ratio of 10:1 using alow tech mini baja cvt and an overall vehicle dynamics package that was far interior to the top 25 percent of the field in 2007 I was convinced of not only the potential but the actual performance of a CVT. The car looked slow as hell on the course in comparison to the herky jerky shifter cars but as they always say, slow is fast. In the least possible terms to describe it the car was always "on the pipe" and made up the time using more area under the curve. "I seent it"-Pinapple Express

2) The chosen CVT to use for a FSAE in my experienced opinion is the Gaged Engineering GX-9 that is taking mini baja by storm currently. I spoke with Bill from Gaged the other day since posting last week in inspiration and we had a discussion about what he could make his newer series of clutches do with 5000 usable rpm (i.e engage at 4000rpm and run out to 9000rpm redline)I could feel his head shaking side to side over the phone in the thought of the fun he could have with that. The primary is a 6" and the secondary is an 8" which would net a 4:1 low ratio and an .8:1 high ratio. Also the belt center to center distance is 9". Assuming anywhere from a 3:1 to 4:1 final drive (explain in a bit) and with the previous rpm and tire rpm requirements we wouldn't need to go so far into the high ratio (i.e we only need an infinite couple gears and not an infinite 6 speed worth of gears) which is easily done with spacers on the primary and/or secondary post to keep the sheaves from moving out of a certain range. With a non adjustable final drive this is how you would adjust your "final drive" through determining where in the huge range of the CVT you would like to be. One would assume you could downsize the CVT to work in your desired range but I would leave it so that you can drive it at larger national SCCA track if you wanted and be competitive since the FSAE course are so tight and not real worldy. So with that in mind at 60mph you only need around a 2:1 high ratio in both tire sizes. 4:1 ---> 2:1 of infinate gears would be brutal spread. Also with a 4:1 Low gear with a 3:1 or 4:1 final drive that will net you a 12:1 to 16:1 crank to final drive axle torque multiplication. That is pretty stiff and much more than the 8:1 or 9:1 you would get with a direct drive in a much smaller box with a much better oops management.

3) Packaging. Z I agree with you in the both senses of longitudinal and transverse mounting options. Here is the link to a post from back in 2007 when I was seriously thinking about directing the team to switch over to a Jawa 500cc. My lean angles are off a bit from yours but i think your longitudinal lean angle would be a bit excessive and not leave the room necessary for a diff. To note I had and still have saved all my technical correspondences with Jawa CZ about what would need to be done to convert the engine for FSAE use. The only addition with a laydown (i.e. vertical crank with transverse engine positioning) would be a dry sump.

Notice the dimensions of main roll hoop centerline to diff centerline. 19" with the briggs twin down to 15.5 with the Jawa 500 in a longitudinal configuration.

http://fsae.com/eve/forums/a/t...10082241#38410082241 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/55310441241?r=38410082241#38410082241)

So that looks good in terms of the traits we are looking for in the "box". But it gets much better. I figured out how to get that number down to 13" which is a partial reiteration from a previous post on this thread. Lay the Jawa down transversely right up against a vertical firewall with the crank snout sticking vertical. Mount the primary clutch to said vertical shaft. Run the belt straight back to the secondary clutch with is sitting on a vertical shaft that uses an atv ring and pinion mounted to a differential or just use the exsisting diff out of an atv. The intake would run straight back and up toward the rear of the car. The exhaust would run toward the firwall but on the jawa the exhaust port is already pointing down toward the ground as it points to the side in its normal configuration in order to avoid the downtube on the Speedway bike frame. In the top view you would have to rotate the engine toward the back on the car about 10 to 15 degrees in order to make enough room for the 180 degree bend of the exhaust pipe to go under the jug and toward the back of the car. On the opposite side of the frame where there is an open space you mount the battery, ecu, dry sump tank,etc in order to equal the weight of the jug and head hanging off the other side. The whole "box" would look more like a letter T from the top view which is awesome for making small rear suspension boxes. This would also be a prime spot to mount a belt driven Rotrex supercharger if more power was needed.

Ok this was a lot and some of my numbers might be off a bit. I worked 10 hrs today and spent 2 hours getting swole at the gym. I wouldn't bother with any bespoke anything if I were to do a single. The Jawa is the best bet and I am sure now that with the popularity in Europe of this competition that Jawa CZ would probably let some motors go a reasonable price. I have been thinking long and hard this last week or so about helping setup up some basics to help proliferate an underutilized transmission type by getting a Jawa and putting together a package that would allow teams to walk into using that engine. I would do this in conjunction/cooperation with Gaged Engineering and hopefully Jawa CZ to provide a FSAE specific package on his CVT for use with the Jawa since it is the best and really only worthwhile PTO engine to stick it on. More cars are using CVT's every year and fully auto manuals are heading in that direction anyway so along with the green fuel economy rules in FSAE it only makes sense to help it along.

11-23-2011, 11:19 PM

Originally posted by Boffin:
240/250kg, no aero. 90ish hp at the wheels, and 70+ nm's
Boffin,

I'm curious. It's a heavish car, but probably maximum power. Your hint suggested you're NOT using 2 gears. Err..., so how many? And where? And what are your lap times compared with Monash? http://fsae.com/groupee_common/emoticons/icon_smile.gif

I looked at your Swinburne website, but like most it only has pictures of older cars, and not much interesting tech stuff about this year's car. http://fsae.com/groupee_common/emoticons/icon_confused.gif
~~~~~o0o~~~~~

Rob,

First up, that Jawa engine (http://www.jawa.cz/products.html) looks very suitable for FSAE. And despite the mangled English, the website actually gives the hard facts, including down-loadable parts manuals. Put your gooey black magic behind that and I reckon you've got a winner! http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

I was going to cover "Neutral" in the next essay, but may as well get it out here. From the above posts it seems a fully disengaged engine is not necessary, and apparently you can just use the clutch. I had the feeling the scrutineers might not like that... Nevertheless, a "proper" neutral is not that hard to add to a chain drive. Just a splined shaft and sliding "dog clutch" to engage/disengage one of the sprockets. Quite common on agricultural machinery.

And once you've done that, it is a fairly simple matter to add a second chain and pair of sprockets, for a second gear. So the dog clutch shuffles back and forth between the two sprockets, with neutral in the middle, just like a regular manual gearbox. This gives an added safety factor, in case one chain breaks. However, chain tension would probably have to be set by idler wheels, though these could also be used to minimise shock loads...

You are right that for a high revving engine the overall transmission ratio has to be up around 10:1. This is too much in a single chain run, so would have to be done in two stages. For example, a lateral laydown single with, say, 2.5:1 chain drive to a 4:1 bevel-gear diff. Or a longitudinal single (lateral crank) with chain drive to a spur-gear driven diff, taken off a small FWD car. This reverses the engine rotation, which can be beneficial. And there are a few other neat ways of doing it, but perhaps for another thread...

However, to get the benefit of a single stage drive you only have to slow the engine down. Rather than having a "screamer", I would prefer a super-charged "thumper". That is, something that burbles around at one power stroke per orange cone!. (A bit of exaggeration there http://fsae.com/groupee_common/emoticons/icon_smile.gif.)

Yes, the S/C is added complication. But it is an easy way to get you up to maximum power (and you can also turbo it, but that's a bit harder). And it gives a tractable engine that has the simpler chain drive. And (possibly?) it makes tuning easier, given the restrictor and intermittent single-suction.

So, eg., lower compression ratio (8:1?) and S/C with double the normal airflow, giving 120Nm @ 6,000rpm = 75kW (100hp) at the crank. With ~5:1 overall ratio and 10" tyres (0.45m OD) this gives 28m/s (~100kph) at 6,000rpm. At 1,000rpm you're doing ~17kph, which with the right tuning is feasible (negligible valve overlap and let the S/C take care of high rpm breathing). Any slower and you slip the clutch.

A couple of important points here. The overall ratio should be "relatively prime", because, for example, if you had exactly 4:1, then the rear tyres would quickly develop two flat spots (because two power pulses per rotation). And the driveline should be beefed up to cope with the large torque pulses, or better yet, some sort of cush-drive used. FWIW the 1,500hp Porsche 917 used "rubber doughnut" type CVs inboard of its axles...

Z

murpia

11-24-2011, 05:08 AM

A bit off-topic, but what's the efficiency of a 'gooey black magic' rubber-belt CVT?

I would expect a conventional motorcycle transmission to be high 90s % efficient, and I know automotive metal-belt & traction drive CVTs are high 80s % efficient.

How do the rubber-belt CVTs compare? Could be significant if you're connecting one to a lower power engine.

Regards, Ian

kcapitano

11-24-2011, 07:28 AM

I really don't want to derail this awesome thread, but I have to make a case for the engine I have wanted to see since first hearing about it; namely the 2011 YZ450F. This engine was designed to reduce the yaw MoI of the MX bike and I think it could be put to the same use in an FSAE car. As you can see from the picture, the cylinder is at an acute angle to the transmission. The cylinder angle would make it a nice fit behind the rearward leaning seat of an FSAE car. Another benefit is the rearward facing exhaust. Without an exhaust to worry about you could jam just about anything that will fit; batteries, ECE, fuel tank, etc, between the engine and the seat without having to worry about temp. What you do about the intake is up to you.

Personally I would still like to have my transmission come with my engine. Maybe I'm missing the point of this thread, but I think of all the "oops factors" that would go into building your own gear reduction or CVT and I just don't like it. As many of you have been saying you probably dont need all the gears, so you could remove 2 or 3 of the 5 and save the weight.

Perhaps I'm missing the point here, so feel free to ignore me if thats the case. Just food for thought. In any case keep the essays coming, this thread is great!

http://kep.index.hu/1/0/109/1096/10968/1096853_cc94a59279c2035f989fa48ec06cb92d_wm.jpg

Big Bird

11-24-2011, 04:08 PM

Agreed on the recent YZ450 motor on all accounts - except it is kickstart. So there is a not-insignificant amount of work adapting a self-starter to it. Oh well...

11-24-2011, 08:55 PM

Speaking of 450's ... I thought I'd post the following specs as a reference to what is possible...
~~~~~o0o~~~~~

Porsche Turbocharged Type 912 Engine (as used on the 1972 917/30 Can-Am of Essay 2)
=====================================

Air-cooled, 5.4 litre, flat-12.

Construction = 12 x individual aluminium heads and chrome-plated barrels, common aluminium crankcase and 2 x cam-boxes, crankshaft with 6 x big-end journals with central gear power take-off.

Bore = 90.0mm

Stroke = 70.4mm, giving 448cc per single cylinder.

Main journal = 57mm (plain, unlike many earlier Porsches that used rollers).

Big-end journal = 52mm (also plain).

Conrod length = 127.8mm c/c.

Piston = Forged, full skirt, 2 compression rings + 1 oil ring, and with cooling oil jets.

Valve Drive = DOHC with buckets.

Intake valve = Single, 48mm? (maybe larger on this bigger bore engine?) at 30 degrees slant.

Exhaust valve = Single, 41mm? (as above) at 35 degrees slant (so 65deg included angle).

Maximum Rpm = 8,000 - 8,500 (depending on source).

Total Weight = ~240kg, so about 20kg/cylinder.

Maximum Power = ~125hp/cylinder at ~2.5bar boost (qualifying tune).
~~~~~o0o~~~~~

Not bad for a 40 year old, air-cooled, 450-single, eh??? http://fsae.com/groupee_common/emoticons/icon_smile.gif

Z

Mbirt

11-24-2011, 09:41 PM

Originally posted by kcapitano:
The cylinder angle would make it a nice fit behind the rearward leaning seat of an FSAE car. Another benefit is the rearward facing exhaust. Without an exhaust to worry about you could jam just about anything that will fit; batteries, ECE, fuel tank, etc, between the engine and the seat without having to worry about temp. What you do about the intake is up to you. Running a CRF450X never prevented us from placing the bespoke items near the base of the rollhoop between the engine and firewall. Remember that there is only one header primary to package instead of 4 radiating a wall of heat.

Most of the packaging benefits of the YZ450 rearward-facing cylinder evaporate after the addition of a developed intake system. Placing the plenum atop the valve cover might work, but the intake tract bend would space the motor away from the firewall and the plenum may begin to encroach upon where you would like to package the driver's head and/or shoulders. We've packaged our headrest directly above the CRF/TRX's valve cover: http://a4.sphotos.ak.fbcdn.net/hphotos-ak-ash4/253417_195312770521056_130002227052111_602851_1099 868_n.jpg

Looking at this picture, I don't think that the crank and transmission would be able to move any further forward if the YZ450 engine were used and an intake tract had to be packaged between the cylinder head and firewall.

The rear-facing exhaust port might actually be better for running the exhaust forward and packaging the length of a reverse megaphone and muffler alongside the driver.

Cool engine, nevertheless.

rjwoods77

11-24-2011, 09:45 PM

Kcapitano,

That motor looks like a good choice indeed. Also I never said make your own CVT or gear reduction. I said get a CVT from Gaged Engineering and then modify a atv differential ring and pinion (i.e. toss the case and use the bits) so there really isn't much oops factor involved. Your post sounds like you didn't read what was discussed so that is why you may have missed the point.

Z,

While we are taking a trip down memory lane if you wanted to do a flat twin how about the Mercedes Benz M291 Flat 12.

http://www.youtube.com/watch?v=teFADi-EjYo

Man o man what a sound that makes.

http://www.gurneyflap.com/Reso...rcedesC291engine.jpg (http://www.gurneyflap.com/Resources/MercedesC291engine.jpg)

http://www.gurneyflap.com/Resources/engineC292b.jpg

Notice the novel intake and exhaust locations.

11-25-2011, 02:27 AM

Originally posted by rjwoods77:
Notice the novel intake and exhaust locations.
Rob, the M-B M291 has a lot in common with their 1950s M196 2.5 litre laydown straight-eight. Both have the same "intake between the valves", but the M196 is "hot side down". The M291 has the same "hot side up" as the current Audi Le Mans winning diesel V-6.

Both M196 and M291 (I guess from the picture) have the same geared central power-take-off from the crank as the Porsche 912 engine (in the 917 car). The flat-12s are thus effectively turned into 2 x flat-6s, giving shorter, stiffer cranks, with less torsional oscillation problems.

The 1950s M196 also had;

*Built-up, Hirth jointed, roller bearing crank, with one piece conrods.

*Desmodromic valve drive of 2 valves per hemi-head.

*Direct fuel injection (ie. into cylinder).

*Fabricated steel cylinder-head units. That is, a forged steel "pot" is fully machined for a one-piece cylinder and head, then I/E ports, etc., are welded on, then ~1mm thick sheet steel water jacket welded around each group of 4 cylinders. Two such 4-pot blocks are bolted to a common alloy crankcase. This "fabrication" was standard M-B racing practice from early 1900s.

The M-B M196s won pretty much everything they entered in 1954 and 1955 (memory?) then one of them went off the track at Le Mans and killed 80 people http://fsae.com/groupee_common/emoticons/icon_frown.gif , so M-B had to retire from racing for a few years...

All good engines, though...

Z

PatClarke

11-25-2011, 05:39 AM

Not quite right Erik, but then I am older than you =] =]

The 196 Mercs did indeed dominate GP racing in 1954 and 1955. The Mercedes that was fired into the crowd at LeMans was the 3 litre sports car version. Much of the car was magnesium so it wet through the crowd like an incendiary bomb. Mercedes withdrew from all motorsport at the end of the year and stayed away a long time.

It is fitting to remember this happened with a German car at a French venue only 10 years after the end of the war. Memories were still raw!

1955 was a bad year for motorsport. In most parts of the world TV was brand new and motorsport was a big deal for people to watch. Thew saw Vukovich burn to death at Indianapolis, they saw the carnage at LeMans and more events that don't come to mind.

The Pope attacked the sport and I remember as a kid in Ireland hearing the priest rail from the pulpit about the evils of motor racing (That was probably about the time organised religion began to lose me) =]

The sport was dealt a mighty blow. In many countries motorsport was seriously compromised by laws written to protect the public from the racing lunatics. In Switzerland, motor racing was banned. In Australia we were saddled with the dreadful 'Speedway act' that killed and maimed many drivers whilst 'protecting the public'.

Fortunately we live in more enlightened times, but every time I see a WRC car sideways at 150kph inches from a crowd, I remember LeMans 55 and the aftermath!

Pat

DougMilliken

11-25-2011, 08:39 AM

The Mercedes that was fired into the crowd at LeMans was the 3 litre sports car version.
Off topic, but interesting (macabre?) history. Our good friend John Fitch was co-driver of that car with Pierre Levegh. Fitch tells his version of the story,
http://www.youtube.com/watch?v=WOAQu4C3yAc News reel footage,
http://www.youtube.com/watch?v=IuKP-rNyiOQ
http://en.wikipedia.org/wiki/1955_Le_Mans_disaster
http://en.wikipedia.org/wiki/Pierre_Levegh
http://en.wikipedia.org/wiki/J..._%28racing_driver%29 (http://en.wikipedia.org/wiki/John_Fitch_%28racing_driver%29)

JWard

11-25-2011, 09:31 AM

Originally posted by Big Bird:
Agreed on the recent YZ450 motor on all accounts - except it is kickstart. So there is a not-insignificant amount of work adapting a self-starter to it. Oh well...

I believe 2011 onwards included electric start. Might be 2012 actually now I think about it. Either way electric start exists on some new version of the yfz.

Mbirt, I too wish that the exhaust and inlet had stayed the other way around, although I suppose you can only really tell how it will package with a good model, or the engine infront of you.

Thank you Mr Milliken, an interesting read! (although I can't watch the youtube videos thanks to my cave age internet connection)

EDIT: I couldnt have been more wrong, there is no electric start.

rjwoods77

11-25-2011, 02:20 PM

I saw/heard this other link when I posted the other one about the flat 12. I really miss the cacophony of very different sounds and engineering approaches that auto racing used to be. 4 rotor engines sound and perform otherworldly. Damn the FIA for banning wankel engines, CVT's and other game changers.

http://www.youtube.com/watch?v...Y&feature=grec_index (http://www.youtube.com/watch?v=En36KWhSjzY&feature=grec_index)

http://www.youtube.com/watch?v...t=PLA90B6080C61F9AFC (http://www.youtube.com/watch?v=x3UpBKXMRto&feature=results_video&playnext=1&list=PLA90B6080C61F9AFC)

(Coulthard looks 12)

JWard

11-25-2011, 02:29 PM

Originally posted by rjwoods77:
I saw/heard this other link when I posted the other one about the flat 12. I really miss the cacophony of very different sounds and engineering approaches that auto racing used to be. 4 rotor engines sound and perform otherworldly. Damn the FIA for banning wankel engines, CVT's and other game changers.

http://www.youtube.com/watch?v...Y&feature=grec_index (http://www.youtube.com/watch?v=En36KWhSjzY&feature=grec_index)

http://www.youtube.com/watch?v...t=PLA90B6080C61F9AFC (http://www.youtube.com/watch?v=x3UpBKXMRto&feature=results_video&playnext=1&list=PLA90B6080C61F9AFC)

(Coulthard looks 12)

Can't check the links out, but would that be the williams f1 video testing a cvt drivetrain? it's so bizarre hearing an f1 car accelerate away at a constant pitch. Very cool video though.

rjwoods77

11-25-2011, 03:39 PM

Yes it is. It wouldn't be as constant pitch as you would think as that video just shows him easing out of the pits. A lot less so in an autocross format. I was driving past RIT in September on the way to do some shopping ( I live in Rochester) and heard the unmistakable sounds of a CVT tearing ass around their parking lots. In utter excitement that they took up the challenge of using the transmission I went to go see what was up. To my dismay and excitement I saw an autocross with about five F500's there. I modeled the 2007/2008 UB car after an F500 so I hold them close to heart. RIT FSAE looked impressive and won the day. The 25 year old low tech car was just behind them but with a much inferior power to weight ratio and I believe less aero benefit.

http://www.flr-scca.com/solo/2011/flr9_raw.pdf

FSAE people would scoff and laugh at the cars if they saw how low tech they were along with the build quality. A design judge would just bust out the sawz-all instead of even speaking at the herasy of design mistakes they are. The chassis and suspensions look 70's garage built as can be. Solid axles and polymer pucks as dampers. They are very deceptive about how fast they are versus how they look. Gooey black magic CVT. Here are a couple vids to spark possible interest.

http://www.youtube.com/user/fl...18D661/7/FNsWWnJV2zc (http://www.youtube.com/user/flrscca#p/c/9DA1E4443718D661/7/FNsWWnJV2zc) (F500 @ 5:03, RIT @ 6:50)

http://www.youtube.com/user/fl...8D661/12/N0p7v6PUw7s (http://www.youtube.com/user/flrscca#p/c/9DA1E4443718D661/12/N0p7v6PUw7s) (F500 run in cockpit from previous vid)

I see CVT's as the next great untapped leap in FSAE when packaged and tuned correctly which really hasn't happened yet. The car I designed that showed up in 2008 finished 20th and it was a really raw untuned version in suspension, engine and cvt that it could have been. Dearborn in 2007 looked to finish top 10 but a cone took out their atv derived lower balljoint in the enduro and both running briggs and stratton v twin lawn mower engines no less. Both cars were incredible looks into what would be possible if the engineering, packaging and team execution fell inline. You can't really talk about "any way to objectively choose engine" unless you speak of the transmission of that power that goes along with it.

11-25-2011, 08:09 PM

Originally posted by rjwoods77:
I see CVT's as the next great untapped leap in FSAE when packaged and tuned correctly...
...
You can't really talk about "any way to objectively choose engine" unless you speak of the transmission of that power that goes along with it.
Rob, I agree 100%.

I go even further and say you can only "objectively choose" your engine by considering THE WHOLE PACKAGE! I'll do one more essay in a couple of days trying to wrap it all up...

The big problem is that it's just too easy for the teams to think "Well, best bet is to do a "standard" car". Of course, it turns out much harder than they think (all those fancy little gubbins to fabricate...). Then most teams fail to complete a short 22km drive, let alone "kick-ass" like they thought they were going to do!

Personally, I think building a standard car is a case of "polishing a turd". http://fsae.com/groupee_common/emoticons/icon_smile.gif I wouldn't go near it, there are far too many "better ways" of doing it. But I'm not allowed to compete, and until a team with a spark of imagination, and a mountain of courage, gets it all together properly, we aren't going to see any change.

Or anything "really interesting"... http://fsae.com/groupee_common/emoticons/icon_frown.gif

Z

PS. Max Mosely and the FIA drones who ban everything should be publicly flogged for their disservice to society. Think of the billions of dollars per year that could be directed to useful devlopments...

rjwoods77

11-25-2011, 10:22 PM

Z,

I used to tell my team the real reason for going at the competition in a different direction (lawnmower v-twin,CVT,solid axle,etc) was because there wasn't a hope in hell in competing in the same arena with well resourced teams (money,facilities,intelligence,daft,etc) if you were going to simulate what they did. We went to competition to spectate since we didn't get the car finished in time and observed Dearborn doing what I had hoped our car would do and did the following year with an 18th finish. UB's formula team has since folded and Dearborn I think gave up on that particular concept so it is up to newer freethinking teams or established giants to take the concept to true fruition. I could only hope someone takes up the reins. On a side not I am speaking with one of my former team members about helping but together a basic package of stuff to help make that fence less forbidding to jump over which would of course follow the intent of the rules and competition.

rjwoods77

11-27-2011, 04:26 PM

Besides all that engineering mumbo jumbo there is the supreme reason to run a cvt...

http://www.strimoo.com/video/1...6-MySpaceVideos.html (http://www.strimoo.com/video/13568727/Buffalo-66-MySpaceVideos.html)

ZAMR

11-27-2011, 04:56 PM

Ok what the hell guys I've seen ppl agree on "you only need two gears" and "the CVT is amazeballs." Well, make up your mind; which one is it?! Do you want inf gears or 2? Can't be both!

Unless you've seen a CVT smoke a conventional gearbox in FSAE...

P.S. Dearborn's '07 car took like 50th in accel or something like that.

Also, for a story about a team with no resources going to compete with the best of the best, read Matt Brown's new book. Consenting to choose a radical but inferior design on the basis of "we can't compete" is what earns you 20th place. Choosing a conventional but solid design and really refining it can get you consistently into the top 5.

rjwoods77

11-27-2011, 06:14 PM

{Ok what the hell guys I've seen ppl agree on "you only need two gears" and "the CVT is amazeballs." Well, make up your mind; which one is it?! Do you want inf gears or 2? Can't be both!}

This is a general conversation with a bunch of different viewpoints so there is no consensus to be had. Also there is nobody saying that they want 2 gears and cvt so your statement just looks rediculous as well as fired off the hip without reading and understanding what we are really talking about.

{Unless you've seen a CVT smoke a conventional gearbox in FSAE...}

I quoted that nobody has really put the package together correctly yet but once it has it will be a shocker and make a gearbox look foolish. Again another rediculous statement by you.

{P.S. Dearborn's '07 car took like 50th in accel or something like that.}

Dearborn was running a 10:1 weight to power ratio and hadn't got their overall package together like they had wanted to hence there slow accel time. They did however whoop on many high ranking teams during the autocross that year which means with refinement on their package they would have whooped on them some more. Again a pointless statement made by you since it was already discussed in previous statements.

{Also, for a story about a team with no resources going to compete with the best of the best, read Matt Brown's new book. Consenting to choose a radical but inferior design on the basis of "we can't compete" is what earns you 20th place. Choosing a conventional but solid design and really refining it can get you consistently into the top 5.}

Some teams, such as ours, had less resources than most and tried to attack the problem in a different/cheaper/less complex method and achieve great results. Those concepts taken further would have netted some even more impressive results. Your statement about radical but inferior is moronic because there wasn't nothing really radical or inferior about it. It was just different and proved some very real merits that needed to be further developed which never came to fruition for either team. Not too long ago people flamed the idea of running a single and look where that is now and continuing to go.

The only thing worth posting in your post was reading his book which I am ordered soon and refining a concept and taking it to the top. So next time take a moment to read through things and make rational discussion points instead of scoffing at the screen while you type nonsense in the effort to make a point that in hindsight would prove to not actually be a point.

ZAMR

11-27-2011, 07:20 PM

Let's not lower ourselves to the level of name-calling, this isn't youtube.

My initial statement was not directed towards you, Rob, but towards Z. You have made your thoughts on the CVT very clear!

I am curious as to Z's thoughts since he has agreed with your statements but has also expounded to us a rather lengthy essay of how Shumy was able to drive an F1 car with one gear. My statement was not meant to belittle Z since I respect his opinions, I just want him to make up his mind! Forgive my rationality.

Is a briggs radical? In my view it is since it is a very different engine than most. Is it cheaper? Hell ya it is. Simpler? Yes. Inferior? Most people would say so. But you CAN win fuel economy. I got to hand it to the Irvine team for that.

bob.paasch

11-27-2011, 08:27 PM

Originally posted by rjwoods77:
I see CVT's as the next great untapped leap in FSAE when packaged and tuned correctly which really hasn't happened yet. The car I designed that showed up in 2008 finished 20th and it was a really raw untuned version in suspension, engine and cvt that it could have been. Dearborn in 2007 looked to finish top 10 but a cone took out their atv derived lower balljoint in the enduro and both running briggs and stratton v twin lawn mower engines no less. Both cars were incredible looks into what would be possible if the engineering, packaging and team execution fell inline. You can't really talk about "any way to objectively choose engine" unless you speak of the transmission of that power that goes along with it.

I respectfully disagree. I doubt we will ever see a car with a CVT ever win a major FSAE/FS event.

First, CVT's are heavy, and packaging in an FSAE car will be heavy. They require about 8:1 reduction from the secondary to the half-shaft. You either need an intermediate shaft for the secondary then a chain to the diff, or a bevel drive diff with a heck of lot of reduction. Either solution adds complexity and weight.

Second, CVT's are inefficient. There's a lot of friction, and they generate a lot of heat. That's your gasoline (or E85) making heat instead of making your car go.

Both of the above are going to kill fuel efficiency. Like it or not, there's 100 points there.

CVT's require a lot of tuning, and that tuning really has to be done on the car as it's hard to simulate the dynamics of corner exit on a dyno. We run the Gaged CVT in Baja, it's great at shiftout but requires a lot of tuning to backshift well. That time could be better invested in areas that generate more points.

I think the same can be said for the bespoke engine. Too much time invested for not enough gain.

The next great leap has already happened: electric drive. Until the rules are changed, I doubt we'll see a combustion car win a combined event like FSUK.

Originally posted by Kevin Hayward:
The recent rule changes to aero have been a real game changer. It was borderline as to whether the extra effort was worth the lap times on the larger CBR cars with the old rules. Now the smaller engined cars are getting more power and there is a dramatic increase in the aero you can produce.

Monash should be very interesting to watch this year. I think the changes to the aero rules may have more long term influence on powertrain choice than the increase in the points allocated to endurance.

Kev

The 2011 aero rules are a game changer of the same magnitude as changing fuel efficiency to 100 points.

rjwoods77

11-27-2011, 08:38 PM

Originally posted by murpia:
A bit off-topic, but what's the efficiency of a 'gooey black magic' rubber-belt CVT?

I would expect a conventional motorcycle transmission to be high 90s % efficient, and I know automotive metal-belt & traction drive CVTs are high 80s % efficient.

How do the rubber-belt CVTs compare? Could be significant if you're connecting one to a lower power engine.

Regards, Ian

That is a tough question to answer because CVT efficiency is based on where in the gear reduction of the transmission you are in. I want to say I remember reading an article stating that a dry belt vs wet belt cvt is more efficient but not used in cars due to the loads involved. I cannot verify that though.

rjwoods77

11-27-2011, 09:39 PM

Dr. Paasch,

I will respectfully disagree with your thankfully respectful disagreement. Pay attention ZAMR as you will notice a different attitude in response.

As far as the packaging requirement of a cvt with a bike sourced 4 cylinder being too heavy and inefficient I will agree. Bradly and Sherbrooke cars in the past showed severe packaging bulk in the past that didnt seem worth the trouble. In this topic however we have been discussing how packaging a CVT with a single or twin cylinder engine would be very efficient and with having done it with a B&S V-twin I can attest to the compactness of it. On page 3 of the pdf you will see the business side of the drivetrain tucked low and close to the firewall (18" tire for visual reference). I also linked a pic to a CAD view with the skin off with a couple reference dimensions as well as a link to the vid of the drivetrain. The final drive we used was a single chain final drive of 6:1. I assume your statement was for 4 cylinder cars because otherwise what you had expressed in terms of packaging is incorrect. I have covered how to package efficiently for single and twin cylinder engines in previous posts in this topic.

http://www.eng.buffalo.edu/Stu...ewsletters/May08.pdf (http://www.eng.buffalo.edu/Students/Organizations/sae/formula_web/newsletters/May08.pdf)

http://i194.photobucket.com/al...7/2007formulacar.jpg (http://i194.photobucket.com/albums/z36/rjwoods77/2007formulacar.jpg)

http://www.youtube.com/watch?v=sqztOLYcwek

As far as reduced efficiency of the transmission I completely agree with you. I will very much disagree with you on that fact that it will suffer fuel economy losses greater that area under the curve gains. In 2008 UB formula finished 2nd in fuel economy and 15th in the combined Endurance/Economy event.

http://www.sae.org/students/fsae2008results.pdf

One of the hardest parts to quantify is how much more area under the curve a CVT vs a geared transmission car as only practical testing will show those differences and I have no such data. What I can provide is a practical example of two different cars competing in the same race but different classes having nearly identical times. RIT FSAE vs a F500 car in a recent SCCA autox event at RIT a couple months ago. RIT's car can be assumed the leading edge of FSAE technology with its carbon tub, full aero treatment,air shifter? and years of development on their 4 cylinder engine and some pretty good drivers. For discussions sake and assuming RIT has the act together they are probably around 375-400lbs and a weight to power around 5:1 --> 6:1. The F500 car has a SCCA declared min weight of 800lbs and assuming the best engine package possible they are running 100hp (again regulation controlled) for a dismal 8:1 weight to power. Then take into account the archaic chassis, suspension (forced to run 73" minimum wheelbase,a solid axle,no hydraulic dampers only polymer pucks),brakes of a F500 compared to RIT FSAE. The RIT should blazing destroy them in every category and have a much better time. The attached results show that is not the case. Also when you watch the videos of the two you can see the F500 understeering into corners and oversteering significantly which is due to the bronze age setup they are forced to run. The only upside to the F500 car is the launch. So of all the horrible things the F500 has to contend with what does it have going for it? Black magic cvt area under the curve. Its the only thing possible that could make up for such a technological disadvantage.

http://www.flr-scca.com/solo/2011/flr9_raw.pdf

http://www.youtube.com/user/flrscca#p/c/7/FNsWWnJV2zc (F500 @ 5:03, RIT @ 6:50)

http://www.youtube.com/user/fl...a#p/c/12/N0p7v6PUw7s (http://www.youtube.com/user/flrscca#p/c/12/N0p7v6PUw7s) (F500 run in cockpit from previous vid)

As far as tuning the CVT goes I will assume you are speaking of OSU baja which by the way is an excellent team. I spoke with Bill @ Gaged last week and he was telling me how difficult it is to tune on a baja when they only really have about 500 to 750 usable rpm to do it in. With a much larger spread of rpm there is supremely much more room to tune with. We didn't have the best tune on our Gaged which was the cause for some of our slowness but I can assure you that the backshift was very nice. It had a nice late 60's 327 high compression off throttle feel to it. If anything I think we were a bit slow on the upshift but that was power related as well. You stated that better time could be spent in better areas but almost all of the possible points we lost were due to an under performing drivetrain. Sales and engineering weren't to bad and with some polishing we could have gotten them much better. I'll have you know that our team, more specifically Ian May, won a powertrain award that year for our setup and analysis.

I think with the current trend of singles in FSAE that modifying a superior Jawa 500 speedway motor to work with a Gaged CVT would be a hands down brute on the track. I disagree that you couldn't win the event with a CVT for the aforementioned rebuttals along with the fact of watching Dearborn in 2007 go into the enduro in 20th? place which just finishing would have put them top 10 and with us securing 18th with a very under tuned and under developed car both of which used a B&S V-twin with a cvt.

I'll agree with you on the electric drive front but what a boring race car that makes http://fsae.com/groupee_common/emoticons/icon_frown.gif

Kevin Hayward

11-27-2011, 10:52 PM

Rob,

I don't think you are advancing your argument by stating finishes in the top ten in endurance are even close to competing for the win. In the results you posted the tenth finisher (which actually had a very good enduro score) was almost exactly 100 points down on the leader in the dynamic points alone. Buffalo (18th) was down nearly 250 points in dynamics alone. These sorts of margins are very large. It is interesting that the RMIT concept (which was and still is a ripper) fell short by nearly 20 dynamic points in this competition.

Bob Paasch is spot on when he makes the claim that the issue is gain for the time/resources allocated is the major problem. If someone was to make a single or twin (with CVT) package available that meant less time for the teams it may end up being competitive. Otherwise it is likely that it is too much of a distraction. A holistic view of the car must be taken in order to compete at the top level, and the most important aspect is to get the team working well rather than having any one sub-system ideal.

With over 400 teams running worldwide and the competition getting closer I think that more custom engines (or heavily modified blocks) are coming. But I doubt any of these concepts will rocket a 20th placed team to a win. They may however end up being the difference between 2nd and 1st.

(Z sorry about the points analysis)

Kev

rjwoods77

11-27-2011, 11:25 PM

Kevin,

My point of return to commenting along with my recent points have been pointing to the possibility of helping put together a package since it seems like the concept has really gone nowhere when I think the combination has extreme merits. After watching that F500 run so close to RIT along with my previous experiences it made me question why it wasn't in FSAE. The answering being nobody has really helped get it over the hump from being a risk to a engineering choice. In reality this whole topic is a distraction since it is a "is there anything else to run besides a 4 banger or a single" so I feel it is worth bringing up.

You are correct that we ate it on the dynamic but much of that was very fixable and with a strong team structure and incremental yearly gains it could have had some very real potential. My point is with a team with good resources can take that concept very far if not to the top. To say that a CVT has no shot of winning in my opinion is a false statement. Developing a car and concept with a CVT would be no different than any other team has done with any of the other technologies to get to the top.

The CVT could actually be a resource saver to be honest if you have a CVT company that offers good tuning services along with a package setup for it. Bill @ Gaged happens to be that. You can send him data logs of your accel runs to help dial in your setups. It has been tough for him to come up with a Baja package due to the fact it operates in such an undesirable range for the unit but FSAE is exactly in the range where it is designed for. His product arrival into Baja about 5 years ago has been a shared learning experience but the package working pretty good now and is the CVT to use. Also you don't have to mess with a shifting and clutching assembly in a shifter car so that wad of stuff is gone. CVT equipped cars have less driver overload as well which makes them a dream to drive and even though they are less efficient that a geared setup they make up for it in other areas. It is an interesting direction to shoot for and one I think could pay some very huge dividends.

Jan_Dressler

11-28-2011, 12:26 AM

Another question: What driver was driving that F500, and what driver was driving the RIT car?

I think sometimes track results should be taken with some care...
In 2008 we were in Italy with a 650 lbs car making about 80 hp. After 1/4 endurance we were stuck in 2nd gear. We should have had no chance at all.
Result? We were third after Stuttgart and Turin. Faster than TU Graz (but they had the better fuel economy http://fsae.com/groupee_common/emoticons/icon_wink.gif).

All in all? Maybe it needs a "top team" with some spare time and manpower to try it with CVT. And maybe that Java engine. And show what this combination can do.

mech5496

11-28-2011, 01:57 AM

So, what makes the best package?
1)High enough torque
2)CVT
3)Low yaw inertia/components near the CG
4)Low CG
5)4WD?

The correct answer?! IMO build a 4WD electric car, with inboard motors and halfshafts both front and rear (keep unsprung masses low that is, maybe moving the brakes inboard as well). Having 4 motors and power limitation at 85kW, those can be lightweight (10-12kg per motor) and based on their inherit high torque output they can directly drive a halfshaft each, so no need for gearboxes an CVT's. Plus you can have 4w torque vectoring based on accelerometers, yaw rate sensors, speed and steering angle...Plus due to really good packaging possibilities of the batteries you can have a low-yaw-inertia car with a low CG. Plus you will have much better efficiency than a combustion car... Weight for the complete powertrain could be at 80-85kg, some 20kg heavier than a 4pot combustion powertrain, but not having in mind components like intake, exhaust, fuel tank, differential, differential mounts, chain etc. The only downside I see on that is the cost, as batteries, motors etc should be really expensive. Boring race cars?!

http://www.youtube.com/user/DU...#p/a/u/0/x8-dj4eDCAM (http://www.youtube.com/user/DUTtwelve#p/a/u/0/x8-dj4eDCAM)

Do not think so...

Now add an aero-pack on that and lots of testing and go smoke everybody in the competition! I must admit it sounds easy...:P

11-28-2011, 05:12 AM

Just briefly... I have a very busy week... I will put this all together in one place (Essay 4) for easier reading at the end of the week.
~~~~~o0o~~~~~

Firstly, although I have been pushing the simple "brown go-kart" for a long time, I have NOT done this so "it's easier to finish Endurance and make top ten/twenty/whatever"(although that would work). I'm too competitive for that. If I could compete I would want outright victory, by a long, long way.

Looking at the problem from "first principles" my conclusion is that the "standard car" is a dud (too heavy, too much front weight%, too high yaw MoI, too many $$$...). I have no doubt that a much faster car can be built with a lot less money and effort.

Sure, that might sound arrogant, but no doubts at all...

In fact, the main reason I am interested in FSAE is that I see it as a great opportunity for someone to do something really interesting (not going to see that in F1 http://fsae.com/groupee_common/emoticons/icon_frown.gif). A low budget team with some smarts could really pull some high-profile pants down, which would be funny... http://fsae.com/groupee_common/emoticons/icon_biggrin.gif
~~~~~o0o~~~~~

ZAMR,

A lightish car with close to maximum power engine (~120hp, which is set by the restrictor, not $$$) only NEEDS one gear. That was the point I tried to make. To repeat, if you can smoke the tyres at the end of the straight in top, and given that you have ~constant torque, then why bother with more torque from lower gears?

However, with a heavier car and less power, you might benefit from 2 gears, at most. My point there was that you can build two speeds into the conventional FSAE chain drive quite easily (extra chain/sprockets + dog clutch, and this also gives neutral and extra reliability if one chain breaks in Enduro).

Furthermore, if heavyish car + low power, then a CVT is a great solution. Perhaps the main reason, as Rob has said many times, is that it makes driving a lot easier. There are also several IVT possibilities (even better because they get rid of the clutch), some using "gooey black magic", but that's another thread...

The important point is that you DO NOT NEED a six-speed sequential 'box, so the whole bike engine rationale starts to fall apart.

You say "Choosing a conventional but solid design and really refining it can get you consistently into the top 5". As I said above, I'd rather win by a long way. It's more fun than "polishing a turd". http://fsae.com/groupee_common/emoticons/icon_smile.gif
~~~~~o0o~~~~~

Bob Paasch,

You say "time could be better invested in areas that generate more points. ... same can be said for the bespoke engine. Too much time invested for not enough gain."

The gain is not from the engine itself, which is just "necessary ballast". The gain comes from having a much better OVERALL package. Namely, one that is not crippled by a gas-guzzling 4-cylinder lump with the wrong shape, too heavy, etc...

IMO most teams invest "too much time" in nonsense that has absolutely no performance gain at all. Eg., self-made hubs/tripods/etc. rather than off-the-shelf units, double-wishbones-with-pushrods-and-rockers, not to mention all the time spent in front of a screen "optimising" their RC migration, etc., etc. Honestly, a lot of that stuff is absolutely pointless, except perhaps in an "educational" way.

The biggest performance gains will come from aero. I haven't seen the "new" rules yet, but even the old rules were enough. No team is close to developing the full potential of aero yet... But that's another thread...

"Electric drive". Dead end. http://fsae.com/groupee_common/emoticons/icon_smile.gif
~~~~~o0o~~~~~

Rob,

If the airwaves around here speed up a bit I might eventually get to see some of your links... Thanks for posting them anyway... http://fsae.com/groupee_common/emoticons/icon_smile.gif
~~~~~o0o~~~~~

Did I say "briefly"???!!!

Z

(Edit.) PS. Harry, just saw your post. An electric car might go well for 22km, maybe even a bit further. But those little electrons just don't have the stamina for real journeys. I've checked, and I couldn't drive to town and back in any electric car on sale today. And the batteries are poison... http://fsae.com/groupee_common/emoticons/icon_frown.gif

Simon Dingle

11-28-2011, 07:03 AM

Z,

Firstly, thank you for your input to this forum over the last few weeks, it's been great to read.

As an encouragement to current FSAE guys thinking about the feasibility of a project like this, i met a student a couple of years ago at my university who made his own single cylinder engine that was based around existing parts. He packaged all the parts and designed and commissioned a cast crankcase to hold it all in. From what I saw it took him just over a year to do it on his own.

Harry,

Plus you will have much better efficiency than a combustion car

I'm sorry, I've got to pull you up on this one. While it might be true for the FSE competition at Hockenheim where they have a solar array and charge the cars from that, in the real world the vast majority of electricity comes from fossil fuel power stations with a max. efficiency of around 48% (that's for gas, it's lower for coal or oil). Then take into account the transmission losses at around 7% (US national average) and the efficiency of the motors at 85% (FSE 2011 average) and you get an overall efficiency of just 34%. While this is marginally better than FSAE combustion cars, it's not any better than existing diesel automotive diesel engines.

I appologise for going off-topic but the efficiency hype that goes with electric powertrains really annoys me.

mech5496

11-28-2011, 07:10 AM

I was just thinking competition, both for the range issue Z mentioned and the efficiency thing...In real life I'd prefer a diesel/petrol engine with no second thoughts. And it's not only an issue where the electricity comes from, there also issues with batteries, how they are built, their small lifecycle and the way of disposal when they are dead, but that's a completely different discussion! (I'm quite sure that including manufacturing and disposal, an electric or hybrid will have a larger CO2 footprint than many of the "conventional" cars out there...)

bob.paasch

11-28-2011, 10:35 AM

Originally posted by rjwoods77:
As far as reduced efficiency of the transmission I completely agree with you. I will very much disagree with you on that fact that it will suffer fuel economy losses greater that area under the curve gains. In 2008 UB formula finished 2nd in fuel economy and 15th in the combined Endurance/Economy event.

Sorry, UB 08 was second in fuel economy because you were slow, nearly 10 seconds a lap off Stuttgart's pace. UB scored 244/400 points. Contrast that to RMIT, who won fuel that year and was only 2 seconds/lap off the top pace, to score 346/400 points. Better yet, look at more recent results: GFR11 at Michigan (2nd in fuel, 1st in endurance, 392/400 points), ETS11 at California (3rd in fuel, 1st in endurance, 394/400 points) or GFR11 at FSG (2nd in fuel, 1st in endurance, 417/425 points). That's the kind of point scoring it takes to win a major competition.

Put enough power through a CVT to actually win endurance and you'll be dropping 40 points in fuel to the lightweight 450 singles. IMHO. http://fsae.com/groupee_common/emoticons/icon_smile.gif

bob.paasch

11-28-2011, 10:45 AM

Originally posted by Simon Dingle:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Plus you will have much better efficiency than a combustion car

I'm sorry, I've got to pull you up on this one. While it might be true for the FSE competition at Hockenheim where they have a solar array and charge the cars from that, in the real world the vast majority of electricity comes from fossil fuel power stations with a max. efficiency of around 48% (that's for gas, it's lower for coal or oil). Then take into account the transmission losses at around 7% (US national average) and the efficiency of the motors at 85% (FSE 2011 average) and you get an overall efficiency of just 34%. While this is marginally better than FSAE combustion cars, it's not any better than existing diesel automotive diesel engines.

I apologise for going off-topic but the efficiency hype that goes with electric powertrains really annoys me. </div></BLOCKQUOTE>

I brought up electric powertrains only in the context of FSAE/FS competitions. We compete under the existant rules, and with the current rules for fuel efficiency equivalent at FSUK, the electric cars are going to be very hard to beat.

bob.paasch

11-28-2011, 10:54 AM

Originally posted by Z:
Bob Paasch,

You say "time could be better invested in areas that generate more points. ... same can be said for the bespoke engine. Too much time invested for not enough gain."

The gain is not from the engine itself, which is just "necessary ballast". The gain comes from having a much better OVERALL package. Namely, one that is not crippled by a gas-guzzling 4-cylinder lump with the wrong shape, too heavy, etc...

IMO most teams invest "too much time" in nonsense that has absolutely no performance gain at all. Eg., self-made hubs/tripods/etc. rather than off-the-shelf units, double-wishbones-with-pushrods-and-rockers, not to mention all the time spent in front of a screen "optimising" their RC migration, etc., etc. Honestly, a lot of that stuff is absolutely pointless, except perhaps in an "educational" way.

The biggest performance gains will come from aero. I haven't seen the "new" rules yet, but even the old rules were enough. No team is close to developing the full potential of aero yet... But that's another thread...
(

Z, I agree with the 4 cylinder engine. I've argued before the power is probably unnecessary and the weight is a killer for fuel economy.

Our decision making process is on the web for the world to see at the latest FSG workshop:

http://www.formulastudent.de/a...0111029-beg-abstatt/ (http://www.formulastudent.de/academy/workshops/20111029-beg-abstatt/)

For us, downforce is more important than CG or HP.

"Electric drive". Dead end. http://fsae.com/groupee_common/emoticons/icon_smile.gif
(

I hope you can get to FSUK or FSE sometime. DUT11 would change your mind.

mech5496

11-28-2011, 11:18 AM

Bob,

I cannot agree with you more (actually I think Simon Dingle's argument was about my post earlier) I was one of the many out there to think "electric cars are lame" but being at FSE this year I have to admit I was more than impressed by cars like Delft, Munchen, ETH, GFR and many others i cannot recall right now. Given the "unfair advantage" of efficiency in the overall point scoring plus the all-available torque, electrics will nominate in a united class for all powertrains. According to your lapsim, there are really big gains in aero, so I would really like to see the performance of an aero-electric car. ETH mentioned something like that in their latest newsletter I think...Any chances of seing a GFR aero-electric entry in 2012?

Adambomb

11-28-2011, 11:44 AM

When we were looking at ditching the 4 cyl in 2008, one engine I took a good hard look at was the Yamaha Fazer 500. It's a snowmobile engine set up for CVT drive; I'm surprised that hasn't popped up with all this CVT talk! It is essentially two YZF-250s siamesed into an inline twin, and as I recall isn't much heavier or wider than a YZF-450. UNM ran this package, I saw it in action at Texas Autocross, it looked very interesting. Biggest downfall is rear packaging, overall packaging the CVT looked similar to Dearborn's, which was a bit ugly with long shafts in bending. In fact I remember UNM having a problem with that particular shaft as well. And in all honesty for the time I spent checking it out I couldn't come up with a better packaging solution without going completely overboard.

While the twin would "play nicer" with the restrictor, the biggest turn-off for that package was with the CVT in my book. I personally know very little about them, and neither does anyone on our team. Main thing I know is that they are good at turning power into heat and hard to tune, in addition to packaging problems. In other words it didn't look like something we could make work well given our time constraints. With that in mind IMO two gears are the way to go, although how you go about it is the interesting thing.

So I still think a single is the way to go. Getting it to "play nice" with the restrictor is the challenge, and a supercharger does sound like the best solution...that is until it comes time for execution. I found a very nice unit from Rotrex that looks like it was made to work with our restrictor, and looking at the maps looks like it would be quite happy with direct drive off the crank. But doing that would spoil the compactness of the single, so you'd pretty much either have to stick the whole thing in longitudinally or else run a belt drive, and either solution would require a good bit of effort to make it work. By the time you package the supercharger and come up with a drive solution, then you end up with something making nearly double the power the stock engine makes, which in turn causes driveline problems down the line, then you need to do transmission work, etc., etc., and the whole unit ends up being so big and heavy that you may as well have a 4 cyl. So that route sounds like something with potential, but would take an enormous amount of development to be competitive...the type of thing that would take probably 9 years of development at an FSAE pace to get fully sorted out.

Then factor in that unless you have an advisor that has the rare traits of being simultaneously active, experienced, and good (ie some semblance of continuity), any idea in FSAE has a half-life of 3 years before being deemed "a crappy idea from some guy that isn't here any more, who probably wasn't as smart/good/experienced as I am." I've been around long enough now to see plenty of that. Or maybe I've just been here too long as a student. http://fsae.com/groupee_common/emoticons/icon_wink.gif Sigh...one more year and I'll finally be released to the real world.

P.S...in case anyone is interested why I've been here 9 years, as the question is posed occasionally, I spent 5 years on a BS including a 9 month co-op, and have been working on a PhD since 2007, although since 2007 I've spent a total of 19 months playing Army with the National Guard. OK, long post, time to get back to work so I can get out of this place some day!

rjwoods77

11-28-2011, 11:56 AM

Dearborn switched to a Phazer twin I think in 2009. I looked at the packaging of one of those and it didn't look advantageous over a 4 cylinder once you stuck the huge primary on the end of the crank and went to chain drive off the secondary shaft the jackshaft and spacing got to be a bit much. Singles and v twins work well with them packaging wise but not much else.

mech5496

11-28-2011, 12:40 PM

I think you mean Phazer and not Fazer http://fsae.com/groupee_common/emoticons/icon_wink.gif Seems pretty nice and we have thought about it when we switched to a WR450, but we stayed away for the reasons you mentioned. Seems like a pretty nice engine though!

http://www.yamaha-motor.com/sp.../566/0/features.aspx (http://www.yamaha-motor.com/sport/products/modelfeatures/566/0/features.aspx)

Simon Dingle

11-28-2011, 01:00 PM

Harry,

Sorry, I thought it was an aside on electric powertrains generally, I'd forgotten that FSUK had combined the classes.

*goes to read the efficiency equivalency rules*

Adambomb

11-28-2011, 02:31 PM

Originally posted by mech5496:
I think you mean Phazer and not Fazer http://fsae.com/groupee_common/emoticons/icon_wink.gif

D'oh! Yes, don't want to get them confused...one is a motorcycle, the other a snowmobile. Ahh, Yamaha and their naming conventions. It's as if nobody talks to each other. Sort of like how they have a Warrior quad and a Warrior v-twin cruiser...

whiltebeitel

11-28-2011, 03:27 PM

We looked at the Phazer seriously with the CVT, but the overall package weight is not very flattering at all, then add on the efficiency loss, the fact that the pistons fire 180 degrees out of phase, it just doesn't add up.Power of a single, weight of a four, more hassle tuning a CVT to work in the range you need it to.

bob.paasch

11-28-2011, 03:38 PM

Originally posted by mech5496:
Given the "unfair advantage" of efficiency in the overall point scoring plus the all-available torque, electrics will dominate in a united class for all powertrains.

I don't think it's "unfair," but it is an advantage and we as teams have to adapt to the rules as they are made. IF GFR goes to FSUK, it will be with an electric car.

According to your lapsim, there are really big gains in aero, so I would really like to see the performance of an aero-electric car. ETH mentioned something like that in their latest newsletter I think...Any chances of seing a GFR aero-electric entry in 2012?

We are still evaluating. With the heavier e-car, the aero is not as effective. The additional drag and aero mass means more battery mass. I'm not sure the points add up to an advantage.

12-01-2011, 05:21 AM

Originally posted by Simon Dingle:
... the efficiency hype that goes with electric powertrains really annoys me.
Simon, agreed.

Electric cars are thought to be "the future" for two irrational reasons;
1. There is a tenous connection with "electronic" devices, which are currently flavour of the month.
2. They don't dribble oil on the floor like mechanical, hydraulic, or pneumatic systems, all of which have better efficiency and power density.

A 220kg FSAE car+driver at top speed of ~30m/s (108kph) has Kinetic Energy =~0.1MJ. (BTW, a MegaJoule is the correct unit here because "mega"="really good", and "jewel"="something precious". A 1 ton car at 100mph has KE=1MJ, as does a 2.5ton SUV at 100kph. Only the engineering industry is stupid enough to use a non-standard and nonsensical unit like "kiloWatt*hour" for energy!)

Really small and cheap toy cars use either a spinning flywheel (little metal washer), or a "clockwork" spring to store energy for their high speed runs. Flybrid built a 0.4MJ flywheel storage system in the early F1 KERS days that weighed less than 20kg (memory?). A ~0.4MJ hydraulic/pneumatic accumulator (ie. an "air spring") would be a bit heavier and bulkier, but possibly cheaper.

Both these non-electrical systems could be fitted to a simple, lightweight FSAE chassis (+aero!) and be a potent force in Acceleration, Skid-Pad, and Autocross. Note that 0.4MJ gets the car from zero to top speed 4 times over, less the tyre and air drag losses, but plus energy recovered during braking. IMO probably faster than an electric car.

But this energy is not enough for the 22kms of Endurance. So add a very small constant speed diesel engine (~10kW?) that continually recharges the energy store. Now you can have high "surge" power, and keep using it for 2,200kms with a feasibly sized fuel tank! Electric cars are not the only option.

Z

12-01-2011, 05:54 AM

Originally posted by bob.paasch:
Our decision making process is on the web for the world to see at the latest FSG workshop:

http://www.formulastudent.de/a...0111029-beg-abstatt/ (http://www.formulastudent.de/academy/workshops/20111029-beg-abstatt/)

For us, downforce is more important than CG or HP.

Bob,

Well, I eventually managed to see your link... (Why all the hurdles? Now another PW I have to remember! http://fsae.com/groupee_common/emoticons/icon_frown.gif)

Anyway, the decision is the right one.

FWIW I reckon you can get a lot more downforce with less drag, less weight and less cost. The key is not to copy current racecar layouts. They are the result of 40 years of rule changes that banned anything good. Better to look at what was banned. http://fsae.com/groupee_common/emoticons/icon_smile.gif

Z

Fyhr

12-01-2011, 07:09 AM

Originally posted by Z:
But this energy is not enough for the 22kms of Endurance. So add a very small constant speed diesel engine (~10kW?) that continually recharges the energy store. Now you can have high "surge" power, and keep using it for 2,200kms with a feasibly sized fuel tank! Electric cars are not the only option.

Z

Will you offer your assistance in the design of the gearbox (CVT?) to couple the diesel to the flywheel? http://fsae.com/groupee_common/emoticons/icon_wink.gif

12-01-2011, 05:43 PM

Originally posted by Fyhr:
Will you offer your assistance in the design of the gearbox (CVT?) to couple the diesel to the flywheel? http://fsae.com/groupee_common/emoticons/icon_wink.gif
Pontus,

I would prefer the hydraulic/pneumatic accumulator for a first attempt. Several small (off-the-shelf) accumulators can be added/subtracted during development according to how much energy you find that you actually need (eg. not much for Acceleration and Skid-Pad). Drive the wheels directly with a swash-plate motor, for variable torque/power. The diesel engine sends oil from the low pressure tank back to the high pressure accumulator with a roller-vane pump, or similar.

For flywheels an efficient IVT can be made using a planetary (epicyclic) gearset, one swash-plate, and one fixed displacement hydraulic pump/motor. Unfortunately, you (might?) need two of these, one motor-flywheel, and one flywheel-axles. I think the flywheel itself may be the biggest problem (eg. high speed bearings?, vacuum canister??, seal for the output shaft???, etc.).

The hydraulic/pneumatic approach is mostly off-the-shelf farm tractor technology. Its main disadvantage is that at some stage several team members are absolutely guaranteed to get covered head to toe with a fine spray of oil. "I thought YOU tightened that joint!" http://fsae.com/groupee_common/emoticons/icon_smile.gif

(Also, I'm not sure if any of this fun stuff is eligible under any of the rules?)

Z

bob.paasch

12-01-2011, 05:50 PM

Originally posted by Z:
(Also, I'm not sure if any of this fun stuff is eligible under any of the rules?)
Z

I've seen hydraulic drive systems in BajaSAE. The accumulators are required to be at zero charge at the start of any event. I would expect the FSAE powers to enforce the same. Makes it pretty worthless for the acceleration event.

ZAMR

12-01-2011, 07:02 PM

Originally posted by Z:

FWIW I reckon you can get a lot more downforce with less drag, less weight and less cost. The key is not to copy current racecar layouts. They are the result of 40 years of rule changes that banned anything good. Better to look at what was banned. http://fsae.com/groupee_common/emoticons/icon_smile.gif

Z

???

I'm pretty sure the front/rear wing configuration is the best wing solution, and sprint car wings would make passing both egress and tilt a challenge. Many other wing solutions have been tried and tested, but do not work as effectively (one wing, three wings, red wings, blue wings, delta wings).

FSAE does not ban active aerodynamic devices, so long as they do not forcibly remove air from under the vehicle, so fan-cars are out. You can however have very light, active elements, a-la Oklahoma where the winds come sweeping down the plains.

You can't scrape, so sealed diffusers are out...

You can also presumably use a fan-wing, provided it is not in ground effect (unless you interpret the rules such that a fan-wing in ground effect does not constitute powered ground effect). Balancing the car would become very difficult due to the complex front-wing/rear-wing interaction.

If you think 3-dimensionally, there is always the possibility of an active "rudder" device which could increase the car's producible lateral force. This however is an ambitious and severe engineering challenge.

So if there's a better way to make aerodynamic downforce that doesn't entail wings, that doesn't use active ground effect, isn't a giant rudder, isn't a sprint car wing, isn't a sprint fan-wing, and still remains in the bounds set by the rules, I imagine the production of downforce has converged to a 2-wing solution for a reason.

Oklahoma's wings from 2011 produced considerable downforce and weighed only ~15lbs (that's ~7kg for the rest of the world, total, both front and rear combined, with active elements, not counting the wing's microcomputer, which was under a pound). I can't imagine there's anything lighter than that which both a.) makes a lot more downforce and b.) less drag, except for a similar configuration that is engineered better.

This doesn't preclude the possibility, I'm just hesitant to believe...

BUUUUUUT this is an engine topic so....... ya...... sorry.......

Fyhr

12-02-2011, 01:29 AM

Originally posted by bob.paasch:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:
(Also, I'm not sure if any of this fun stuff is eligible under any of the rules?)
Z

I've seen hydraulic drive systems in BajaSAE. The accumulators are required to be at zero charge at the start of any event. I would expect the FSAE powers to enforce the same. Makes it pretty worthless for the acceleration event. </div></BLOCKQUOTE>

The one competition where accumulators definately are not required to be empty at the start of an event unfortunately have this definition of a hybrid:
"A Hybrid vehicle is defined as a vehicle using a propulsion system which comprises both a
4-stroke Internal Combustion Engine (ICE) and electrical storage (accumulator) with electric
motor drive"

Speaking of hydraulic drive, I vaguely recall talk of a AWD FSAE car with hydraulic wheel motors for the front wheels, did that ever exist or is it only memories of late night discussions with KTH students?

Relevant component source: http://www.gizmag.com/go/3180/

12-02-2011, 06:22 AM

Bob and Pontus,

Yes, the auto industry does like to manage its innovation. Some alternatives are clearly more "equal" than others. http://fsae.com/groupee_common/emoticons/icon_frown.gif
~~~~~o0o~~~~~

ZAMR,

I haven't seen Oklahoma's car, and not sure what you mean by a "fan-wing".

The way I see it the best downforce is made close to the ground. Skirts are not necessary, but the right shape underfloor, and how it is "driven", has huge potential (check the history books, and they were just starting when they got banned). Conventional rear wings make good air-brakes.

But perhaps better left for another thread...

Z

rjwoods77

12-02-2011, 09:03 AM

Z,

T88?

ZAMR

12-02-2011, 10:27 AM

Originally posted by rjwoods77:
Z,

T88?

That would be cool if someone could pull it off, especially without ground clearance rules. You would just have to be absolutely sure not to srape, which is more difficult than it should be. I know UTA tried some variation of it one year but decided to abandon it for weight reasons. Hard to tell if you could get more downforce than wings. Interesting.

flavorPacket

12-02-2011, 12:33 PM

Originally posted by Z:
They don't dribble oil on the floor like mechanical, hydraulic, or pneumatic systems, all of which have better efficiency and power density.

There are electric motors in production cars putting out over 400 Nm torque while weighing less than 60kg...can you share an example of any of these other drive systems exceeding that density in a type-approved, mass-production product?

[/threadjack]

ZAMR

12-02-2011, 01:11 PM

Kirk Feldkamp

12-02-2011, 01:48 PM

Originally posted by flavorPacket:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:
They don't dribble oil on the floor like mechanical, hydraulic, or pneumatic systems, all of which have better efficiency and power density.

There are electric motors in production cars putting out over 400 Nm torque while weighing less than 60kg...can you share an example of any of these other drive systems exceeding that density in a type-approved, mass-production product?

[/threadjack] </div></BLOCKQUOTE>

Who cares about the torque? Torque can scale and shift around all over the place with gearing all day long... the power density is really what you care about. Gearing, even within reasonable limits, makes it completely possible to overcome the tractive limit of the tires on FSAE cars (and most vehicles) even with not a lot of input torque. Good luck changing how much power is made at any given point. When you consider the power density of the *whole system* (as you would have to when comparing the various options), the power density of a full electric system tends to suck pretty hard compared to a liquid fuel source.

This has been a major gripe of mine when considering the various off-the-shelf electric motor options right now. For some reason the electric motor market has moved toward larger, higher torque, lower power motors... presumably because it allows manufacturers to avoid including a transmission, and just running it as a single speed. I think a lot of companies got spooked by the Tesla debacle with their two-speed transmission. From what I gather, that was an avoidable situation that was driven by marketing and early promises made before pre-production durability testing could really take place. Anyway, if gearboxes came back into the picture, the electric motors could be transformed into higher RPM, lower torque variants that not only cost less to produce, but also have a better power density and average operational efficiency. That's a win-win in my book. The single speed concept suuuucks for energy efficiency at lower and midrange speeds, where you spend a large proportion of time during city drive cycles.

Scott Wordley

12-02-2011, 01:59 PM

I think Z's thoughts on obtaining better aero definitely deserve their own thread, but a few comments... (at the risk of further thread hijack)

UTA did run a separate, floating, unsprung diffuser, in 2002 I think. I think the wings were mounted to it as well. Nice for maintaining a consistent ground clearance but difficult to rigidly constrain without it acting as a non adjustable roll/pitch bar. That's probably fine at high speeds once the aero overwhelms the mechanical grip, but not for the range in which a fsae car generally operates. We didn't think it was worth the effort and extra hassle given the forces involved and are happy to take the diffuser load through the suspension (wings unpsrung though). UTA went away from the concept from memory.

I have found that realistic data on diffuser performance is very hard to come by. If you build a diffuser, put it on your car and expect similar performance to the more fundamental literature (eg Ahmed body stuff, or idealised group c sports car), you are crazy. Fsae cars are very messy aero wise, being relatively bluff, and "up and down" rather than long, low and lean. Practically every FSAE diffuser I have seen terminates in the messy wake behind the driver and engine.

Earlier in this thread Z and others made the very good point about minimizing your mass, lowering it and centralizing it, via the engine choice and car layout. I agree wholeheartedly with this philosophy. Minimize weight as a priority, lower whatever mass you must carry as much as possible, and where possible centralize the lowered essential weight.
Personally I rate cg height reduction as more important that minimisin polar moment of inertia, as cg height ultimately sets the practicable lower limit on your track width, the importance of which has been discussed extensively in other threads. Most teams are also right on the lower limit of wheelbase too, for the above reasons.

The point of these observations is that your diffuser wants to be as big as possible. More area = more down load. Even with the extra package space (+300mm from and rear) these days, you are not left with much real estate to play with. Your tunnels end up squeezed tight between the driver/engine and wheels, and conventional wishbones create sealing issues if you try to run really aggressive and overly optimistic tunnels. As any observer could see from the diffuser designs appearing recently, many appear quite conservative. That's all you can reliably get out of them according to our CFD work. I would not consider widening or lengthening a car to allow more underbody, but some teams (ie Maryland) seem to make it work, but they probably also have other reasons for their wheelbase choice (like rear weight bias).

Coming vaguely back to the original thread topic, perhaps a custom engine, cvt and car layout could be developed to be more subservient to the wants of aero, if you considered it THE major priority? We thought long and hard about it, and while a side engine could have some benefits it was still far from ideal.

Consider this. At VERY best, and crazy as it might sound, say your entire car/driver/diffuser COULD be shaped like a huge single element wing in ground effect. Ignore the wheels, assume optimal and constant ground clearance, endplates/seals and also ignore the terrible aspect ratio (well "oversquare"). Calculate how much downforce that would make. Your probably looking at a CL.A of 5 - 8? I think the serious aero teams are already close to, if not in that range. Done well wings can make much higher Cls than diffusers, whilst potentially helping to improve their performance. Yes the drag penalty is greater, but that's diminishing returns for you!

So IMHO diffusers and underbody trickery is part of the puzzle, but not a complete solution in and of itself.

I think wings are practically irreplaceable given our current knowledge and techniques for extracting downforce from the oncoming airflow.

Front and rear wings may be an obvious choice, but there are good reasons for it, as I'm sure Z knows. If you can use ground effect, you should do so (ie the front) for increased CL and L/D Ratio. Win-win. The rear wing goes as low as it can to catch enough clean flow to generate enough downforce to balance the front. This leaves a convenient hole in the middle for the driver to enter and exist the vehicle!

Anyway, I have a feeling Z is talking about something different though, something with potential for very high Cls. I have never seen them used on a race car though... Looking forward to the conversation! Have missed this game, "try and guess what Z is thinking". Good conversation starter

Scott

Kirk Feldkamp

12-02-2011, 02:19 PM

Originally posted by Scott Wordley:
At VERY best, and crazy as it might sound, say your entire car/driver/diffuser COULD be shaped like a huge single element wing in ground effect.

In many regards, that's sort of what you've got with a "prototype" style body, right? The differential pressures between the top surface of the body and the lower surface of the diffuser are the upper and lower surfaces actually generating the downforce. I was actually thinking about that last night, and dug into the rules a bit. The rules are remarkably ambiguous and undetailed about what features constitute a "formula-style" and "open-wheeled" body. It says it in the beginning, but doesn't say anything about it in the aerodynamic section. I'd argue you could get 1 metric asston (like the units Z?) of downforce on a FSAE car if you had an open-cockpit ACO "prototype" style body with simple openings around the wheels to meet the open-wheel requirement. Without definition in the rules about what constitutes "formula style" bodywork, I think they'd be hard pressed to tell you your design couldn't pass tech.

flavorPacket

12-02-2011, 02:55 PM

Originally posted by Kirk Feldkamp:
Who cares about the torque? Torque can scale and shift around all over the place with gearing all day long... the power density is really what you care about. Gearing, even within reasonable limits, makes it completely possible to overcome the tractive limit of the tires on FSAE cars (and most vehicles) even with not a lot of input torque. Good luck changing how much power is made at any given point. When you consider the power density of the *whole system* (as you would have to when comparing the various options), the power density of a full electric system tends to suck pretty hard compared to a liquid fuel source.

This has been a major gripe of mine when considering the various off-the-shelf electric motor options right now. For some reason the electric motor market has moved toward larger, higher torque, lower power motors... presumably because it allows manufacturers to avoid including a transmission, and just running it as a single speed. I think a lot of companies got spooked by the Tesla debacle with their two-speed transmission. From what I gather, that was an avoidable situation that was driven by marketing and early promises made before pre-production durability testing could really take place. Anyway, if gearboxes came back into the picture, the electric motors could be transformed into higher RPM, lower torque variants that not only cost less to produce, but also have a better power density and average operational efficiency. That's a win-win in my book. The single speed concept suuuucks for energy efficiency at lower and midrange speeds, where you spend a large proportion of time during city drive cycles.

So much to say here...I'll leave it for another thread.

ZAMR, yes you're right about batteries. But BMS density improves 8-12%/yr in production (much more in the lab). If that continues, and that's a big 'IF', 100 RON gasoline isn't too far off.

Back to the original thread, I'm simply trying to point out that electric powertrains offer significant performance and packaging differences that can be exploited to great effect. FSAE teams are starting to use sims to perform dynamic score sensitivity analysis, so let me ask this: what happens to your score when CG drops 30% and mass goes up 15%?

12-02-2011, 08:33 PM

Wow, I'm still trying to slip in Essay 4.....
~~~~~o0o~~~~~

Rob, ZAMR, Scott, Kirk, (re. aero),

My main general points are;
1. 2-D wings have more lift + less drag than 3-D, because of 3-D vortex losses (see Lanchester 1895, Prandtl 1902?, etc.).
2. A wing close to the ground behaves 2-D-ish (see "ground effects", "Caspian Sea Monster", etc.).
3. A largish "aero-floor" (or "floors" http://fsae.com/groupee_common/emoticons/icon_wink.gif) would not be hard to fit on a FSAE car, and could be lightweight and would have low CG anyway. But planning the rest of the car with this in mind would be necessary.
4. Having aero-floor loads act directly on the hubs, like the T88, would be easy (with pre-planning), and beneficial.

Specifically, Scott, you say "Done well wings can make much higher CLs than diffusers." I disagree. A wing is a wing is a wing... If you put a wing close to the ground it works better than high up. To work even better it should now be a different shape because of the influence of the ground. If you make it a flat plate with some crude diffusers, then it is not a very good shape. If the diffuser "terminates in the messy wake behind the driver" then it is even worse. But done right it is a "wing" that generates huge CL with minimal CD.

The "history" I mentioned referred to ALL the race series that were given a bit of freedom with their underbodies. Downforce and corner speeds always shot up, top speeds increased (because of negligible drag increases), and the series organisers promptly banned them, or at least tightly regulated the underfloor shape.
~~~~~o0o~~~~~

Ryan (fP),

As Kirk explained, it's about the power density of the whole package.

In a previous life I used to work in the "materials handling" industry. Mostly food packaging, everything from wrapping little lollies (sweets) in small squares of foil, to folding big cardboard boxes around lots of smaller boxes. We used all four means of transmitting power, namely through a solid, liquid, gas, and the EM "aether" (ie. mech/hyd/pneu/elect).

The efficiency and power density went in the same order, with electric by far the worst. But the customers usually wanted all electric machines. The main reason, as I said before, is they don't "piddle on the floor", like a naughty puppy dog. http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif

The mechanical systems (cams, linkages, etc.) are best by far, but expensive. Hydraulics have awesome power density (look at any earth-moving machine), but are always pissing messy oil everywhere. Pneumatics never stop hissing, and also occasionally wet themselves. By comparison the electric systems (eg. stepper motors, solenoids, etc.) are very heavy, bulky, and surprisingly noisy, but they don't leave that puddle on the floor... http://fsae.com/groupee_common/emoticons/icon_smile.gif

(Edit: You ask - CG height drops 30% + mass up 15%?
IMO, if the car wasn't falling over before, then this is a backward step (getting too heavy). But if it is prone to falling over, then you have to lower CGheight/track.)

(Essay 4 tonight...)

Z

12-03-2011, 02:28 AM

Essay 4. Putting it All Together, Objectively.
==============================================

To conclude these Essays, I will consider the broader subject of "objectively analysing the whole competition, with some reference to the engine". Much of what follows is covered in Geoff Pearson's "Reasoning..." thread, but hopefully some repetition won't hurt.

It seems to me that the majority of students entering this competition have the preconceived idea that they are supposed to build a smallish Formula One car. Along the way they believe they will have lots of fun driving "a real racecar". And after it is all over they will have an impressive entry on their CV that will open doors to pretty much any hi-tech job they want. Sometimes this happens. But just as often reality sticks its ugly head in the way, and the car and all the effort that goes into it is an unedifying disaster.

An apparently much smaller number of students see this competition as nothing more than a "puzzle" to be solved. The puzzle is; "How do we score lots of points, so we can be 'The Winners'?". Solving this puzzle requires an objective analysis of the FSAE Competition Rules, and the Rules of Nature.

This analysis roughly corresponds to "Level 4 Reasoning" in Geoff's thread. So, for the next few paragraphs, try thinking in this objective way, and forget any preconceived ideas you might have about how "real" racing works.

To begin this process, you don't have to be a genius puzzle solver (you can check the history of the event) to realise that to score well overall, you must;

SCORE POINTS IN ALL EVENTS.

Put simply, this just means "being there". Not arriving late (or worse, not arriving at all!). Not telling the scrutineers "Yeah but..., nobody told us we have to do that...". Etc, etc. And a big part (two thirds) of the above is that you must;

FINISH ALL DYNAMIC EVENTS.

Put simply, this just means having a car that "goes". All you need is a car that can get through scrutineering, and then move under its own power for about 30kms without falling apart. Frankly, this is not a difficult thing to do. As explained many times on this forum, if you do the above you will score more points than half the other teams.

But what if you want to score more points than ALL the other teams? This is a natural thing to want to do, boys being boyshttp://fsae.com/groupee_common/emoticons/icon_smile.gif. And here begineth the problems. Most young men think that to win any motor race requires a lot of power. Or at least high power-to-weight ratio. Or maybe just a lot of noise and burning rubber. Well, it isn't that simple...

~~~~~o0o~~~~~

The very important point to understand is that in FSAE, and autocross in general, the Rules of Nature tell us that high power is NOT at the top of the list of priorities. A "Level 3 Reasoning" type analysis suggests that to be fast you need a car that is easy to drive quickly in and out of tight corners. Lots of corners. As explained in Essay 2, it is relatively easy in FSAE (compared with other Formula) to reach the "Donohue limit" of having more than enough power. While this can certainly be fun, it is not necessary if your goal is to score lots of points.

So what is needed to score lots of points in the Dynamic events?

1. RELIABILITY. This is most important, because you have to finish all events.

This is best done with a simple car, because it has less things that can go wrong, and is built more quickly giving more time for testing (see more below).

2. AN AGILE CAR. One that is fast to turn-in, drive through, and turn-out of a corner, and then do the same over and over again. What makes a car agile?

2.1 STICKY TYRES. But these are a "bought" item so everyone has the same potential advantage from them. Note that the mass of the car only has a 2nd order effect on performance, this coming from Tyre Load Sensitivity. Since most FSAE cars are over-tyred this TLS is only a small effect, so heavy cars can corner steady-state about as fast as light cars, all other things equal.

2.2 LOW YAW INERTIA. This is a 1st order effect on performance of the car as it transitions in and out of corners. For the same wheelbase and car mass, equal grip tyres can rotationally accelerate a "cannon-ball" faster than a "dumb-bell". This is a geometrical effect, not related to TLS. The bike engines of most FSAE cars force them to be dumb-bells, so there is a significant advantage available here.

2.3 HIGH AERO DOWNFORCE TO MASS RATIO. This is the largest 1st order effect on performance. The funny thing is most high downforce FSAE cars also seem to be quite heavy, possibly because aero is thought to require lots of money, and lots of money leads to a highly tuned but heavy turbo'ed 4-cylinder bike engine with paddle-shift sequential 'box. For a given amount of downforce, a lighter car is a 1st order improvement to performance, and less time spent developing a heavyweight powertrain gives more time to improve the aero.

3. LOW FUEL CONSUMPTION. This is becoming more important as the man-made rules change. Nature's rules suggest that a "constant speed" car that is fast enough through the corners that it doesn't have to accelerate and brake too much (or at all) will be the most fuel efficient (because braking is fuel down the drain). This in turn suggests that only a lowish power engine with a single gear is necessary. Potential points lost in the Acceleration event, due to a lack of power and gears, can be made up by having a light car and the proper launch technique (the first 5-10m is most important). But more importantly, there are many more points on offer in the other Dynamic events, and they don't require much power or many gears.

~~~~~o0o~~~~~

So, if the above objective Level 3 analysis makes sense, then what Level 2 features should you design into the car? Some suggestions;

Firstly, realise that the standard 4-cylinder-bike-engine-with-sequential-box is spoiling the overall design. Spend a bit of time finding, modifying, or building an engine/drivetrain that will give a better overall package. See the many earlier posts for more detail.

Secondly, save a lot of time and money by simplifying the chassis and suspension. Personally, I like suspensions. At one time I was suggesting that the organizers make the tracks much bumpier than they are, so that good suspension would be a winning advantage. It didn't happen. Current FSAE Dynamic events can be easily won with no suspension at all. But +/- 25mm is required by the Rules.

So use the simplest suspension you can. Beam axles have many benefits and only require a few "hard points" on the chassis (eg. 3 per end, which simplifies the chassis). If you must have independent suspension, then lateral or longitudinal swing arms are more than adequate, and also give a simple chassis. Any more complexity is unnecessary. There are many details here, but perhaps for another thread.

Note that ultimate grip and handling balance come mostly from the static settings. These include the tyre brand, size, compound, air pressure, toe, and camber. It is only the very last bit of fine tuning that requires changes to spring rates. At the very most you need only one ARB. Because of low car mass the dampers only need to be "just enough", so don't waste money on more.

With the above in mind you can begin the overall car layout. Start with the most essential parts, the four tyreprints and the centrally located driver's seat. Next add only what is absolutely necessary, or required by the Rules. So the "necessary ballast" of the engine should be barely visible, being tucked away under the seat back. The suspension should radiate out from the centralised major masses of driver and engine, to the tyreprints. The mandatory roll hoops, foot box, and side impact structures, now make up most of the chassis. Likewise, minimise and simplify the steering system, brakes, and anything else you can.

Finally, with the car finished early and testing underway, start fitting the aero parts you planned from the beginning. Now see how much faster you go. http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

~~~~~o0o~~~~~

Well, that's my vision of what is objectively required to "score lots of points". A working car would explain it better, but that's the best I can do with words.

Z

flavorPacket

12-03-2011, 11:46 AM

Originally posted by Z:
(Edit: You ask - CG height drops 30% + mass up 15%?
IMO, if the car wasn't falling over before, then this is a backward step (getting too heavy). But if it is prone to falling over, then you have to lower CGheight/track.)

Let me run with this one for a moment. If a FSAE car gets a lower CG, it can reduce its track width. In FSAE, narrower track widths mean higher slalom speeds/faster transitions (not the case for all vehicles, but for FSAE this is essentially always true). So the tradeoff is: how much faster will you have to go in order to offset the mass penalty?

12-03-2011, 05:08 PM

Originally posted by flavorPacket:
So the tradeoff is: how much faster will you have to go in order to offset the mass penalty?
Ryan,

You now have the extra parameter of Track width (in addition to CGheight and Mass), so it all gets a bit trickier. Less T is good for the slaloms, but it also means less A (in CL*A) which might be worse for long, high speed corners. And so on and on...

I very much agree with the idea of doing simulations, even back-of-the-envelope ones. It only takes a few simple simulations to show that different terrains favour different types of cars.

One warning about "sensitivity analysis". When you do a multi-dimensional analysis (lots of parameters) the "optimal landscape" can have many different "peaks". Sensitivity analysis will take you from half-way up a hill to its peak - the "local optimum". But often this approach won't tell you that there is a much higher peak on the other side of the landscape.

"You can't cross a chasm by taking small steps."

Z

flavorPacket

12-03-2011, 05:31 PM

Originally posted by Z:
One warning about "sensitivity analysis". When you do a multi-dimensional analysis (lots of parameters) the "optimal landscape" can have many different "peaks". Sensitivity analysis will take you from half-way up a hill to its peak - the "local optimum". But often this approach won't tell you that there is a much higher peak on the other side of the landscape.

"You can't cross a chasm by taking small steps."

Z

Absolutely (my thesis was on nonlinear optimization). Which is why I often ask how people set limits on their design spaces and if they do any sampling (e.g. latin hypercube) to robustly explore them.

Kevin Hayward

12-04-2011, 01:07 AM

The concept of local vs. global optimisation is a very important one, and one very easily explained. We all know that more weight is bad, but downforce is good. However we need to add weight to have downforce generating devices.

The FSAE event is a very good one for approaching optimisation problems. Not only are there enough rules freedom to force you into global optimisation, there is also a fairly complicated objective function. More interesting is the game theory that could be applied.

Take the example of performance vs reliability (or not taking risks). Both performance and reliability are very important and the purist would say that we can have both in spades. The realist in me disagrees. There are too many options where performance comes at the sacrifice of reliability and vice versa. Now we should look at the competitive nature of the competition.

Imagine that performance and reliability are dependant (i.e. you increase performance, you lose reliability and vice versa). This is not entirely reflected in reality, but will help us set up a simple game.

We have two teams:
- Team A wants to go faster than team B, team B wants to be more reliable.
- If team A finishes it will win
- If team A does not finish it will win

In this case the strategy is very clear. Team B has no motivation to improve performance. In fact it is best to sacrifice all performance for increased reliability. The strategy for team A is much more interesting. Generally it would want its performance only slightly higher than team B such that its reliability is enough to secure the finish and hence the win. There is no point having a much higher performance where reliability must be sacrificed.

Now look at the possibilities:
- Both teams have high reliability and low performance. Team A will finish and win quite often.
- Both teams have low reliability and high performance. Team A is only slightly better off than team B as both are unlikely to finish. The win will be a case of who finishes.
- Team A has low relibility and high performance. Team B has high reliability and low performance. Team B will most likely win because team A will not finish.

Now lets expand this. If we have a competition of 2 teams either strategy works reasonably well. We can call this the Peugeot vs Audi LMP1 battle. As we add teams it gets worse for teams focusing on reliability. For a team to win all the teams with a high performance must fail to finish. As the team numbers increase this becomes increasingly unlikely.

So how does this affect our designs:
- Designing for a small comp is different than designing for a large comp. Reliability will net higher rewards for a competition with less entrants. Converesly in a larger competition it is more likely that a team that takes risks for performance will be more likely to win. However it might be more diffciult to pick the winner.

- If we find something that will absolutely improve both reliability and performance it is valuable.

- If you are not after the win, but instead after good placings then focus on reliability. A well finished and reliable brick of a car will still place well enough to be proud of the place number. The strategy of a team chasing a top ten should be markedly different than a team chasing the win. To win you should be prepared to take big risks.

- If you are not taking risks (i.e. conceptual changes against the norm) the chance is that you are not a team with a fighting chance of a win in any but the smallest of competitions. Be aware of cause and effect here. A winning team will take risks and change the norm. However the inverse statement a team that takes risks and changes the norm will potentially win is not true.

- You should know your competitors very well. If you can accurately assess the required level of performance of winning teams and the reliability of the competitions. If you can make a game changer you have the potential to be very successful. I would call a game changer a car with either significantly more performace with no drop in reliability, or one with close to top performance with huge reliability. I would say that GFR/UWA might fit into the first lot and Stuttgart/RMIT in the second camp.

Up til now this has been a direct trade-off between reliability and performance. The reality is far from the truth. In order to gain performance as a team you need to have reliability. Too much of your performance comes from testing to do otherwise. Secondly reliability is linked to experience in a team. This should be a relief to new teams. It is almost impossible to beat a top runner in your first year. However it is much more likely that a lot off effort could net you a top 10. I would not worry about performance at all in the first year or two. Get an engine running, and try to find something that needs little to no mnodifications and will run with little to no effort. Buy as much off the shelf as you can and test a lot. As you proceed as a team you will need to take more risks in order to climb the ranks.

It is only when you are in the top ten (or higher) that your engine choice will have a significant impact on your points score.

Kev

Thrainer

12-04-2011, 06:36 AM

Originally posted by Z:
They don't dribble oil on the floor like mechanical, hydraulic, or pneumatic systems, all of which have better efficiency and power density. ...

As Kirk explained, it's about the power density of the whole package.

I'm not aware of any racing car with hydraulic or pneumatic drive, so your statement seems a bit weird. Can you prove your point with some examples?
I would agree if you were taling about shifter mechanisms (e.g. pneumatic lighter than electric), but not for propulsion systems. You didn't mention any weight assumptions for your "farm tractor hydraulic/pneumatic" approach.

Since this is about FSAE, let me add one example, two FSAE cars with similar concept (13" wheels, monocoque, no wings) and somewhat similar teams:
- nb011 from Munich weighs 184 kg, max. power of 92 bhp, 3.847 s in acceleration, 24:49 minutes in endurance and 8.050 kg of CO2 produced (data from team website, results from FS Austria 2011)
- novena from Zurich weighs 181 kg, max. power of 94 bhp, 3.752 s in acceleration, 24:22 min in endurance and 4.026 kg of CO2 produced (data from team website, results from FS Austria 2011)

Now, how is electric heavier, less powerful and less efficient than combustion? Maybe a visit to FS UK, FSG or FS Austria would change your mind.

Thank you Scott, Kevin, Bob and Z for the interesting posts in this thread.

Regards
Thomas

nowhere fast

12-04-2011, 07:57 AM

Some (most?) 2 wheel drive motorcycles use a hydraulic drive to the front wheel. I’m no expert on electric motors, but I think an electric drive to the front wheel would be prohibitively large and heavy in this application.

Using fsae cars as an example to compare the weight and power of electric and combustion is probably a little unfair since the combustion car has an inlet restriction. Stock 4 cylinder 600cc engines produce around 120hp. If the combustion car was designed without a restrictor it should make at least this much power, without much change in weight. Admittedly I am not familiar with the rules for electric fsae cars, so I might be wrong on this point.

12-04-2011, 09:27 PM

Originally posted by Thrainer:
I'm not aware of any racing car with hydraulic or pneumatic drive, so your statement seems a bit weird. Can you prove your point with some examples?
...
You didn't mention any weight assumptions for your "farm tractor hydraulic/pneumatic" approach.
...
Now, how is electric heavier, less powerful and less efficient than combustion? Maybe a visit to FS UK, FSG or FS Austria would change your mind.
Thomas,

It is not possible to prove anything on these forums (not enough bandwidth). I was expressing my views on Mech/Hyd/Pneum/Electrical devices, based on my usage of them in directly comparable situations.

As Nathan says, ICE FSAE cars are handicapped by the restrictor. As I have said before, the standard layout FSAE car is not very good to begin with. Nevertheless, put the ICE and electric FSAE cars in a 220km race (still not very far) and the electric cars wouldn't have a chance.

There is a huge amount of bias shown towards electric cars, both in FSAE and the wider world. The fact that Kinetic (flywheel) or Pneumatic (the "P" is just a spring) energy storage are not even allowed to compete in FSAE is some proof of that bias. If anyone really believes electric cars are better, then I have some wonderful "snake oil" you might be interested in. Special price for you... http://fsae.com/groupee_common/emoticons/icon_smile.gif

As a comparison of Electric vs Hydraulic, consider Power Steering sytems. New "EPS" sytems are coming onto the market, often with claims that they have similar, or even less, mass than the traditional HPS. But this comparison is between the electric motor sitting on the R&P, versus the whole hydraulic system including the engine mounted pump. A fairer comparison would include part of the electric alternator and battery, which would make EPS a lot heavier. Or, if the car already has a central hydraulic system (like most Citroens since the 1950s) then the extra bits for HPS are much lighter than the extra bits for EPS. Compare apples with apples...

BTW, please don't anybody quote masses of hydraulic systems off tractors or earth-moving machines. These vehicles always come with huge cast iron ballast weights, because more tonnage = better! That, plus the harsh environment, means any hydraulic pumps and motors are always encased in massive iron or steel castings (no woosy aluminium here). But the internal hydraulic components are actually quite small. The (big!) diesel engine of a 50 ton excavator typically sends all its power into a pair of swash-plate hydraulic pumps that you can hold in the palms of your hands. Seeing the awesome work those little pumps can do is really quite frightening...

Z

dazz

12-05-2011, 03:43 PM

Originally posted by Adambomb:
Z, perhaps something a bit like this? I'm a huge fan of the package, solves all of the problems you mentioned and it certainly looks achievable. Dazz, anything come of this lately?

Sorry for the late reply, been a bit busy with uni, work and a house extension.

Adambomb, I got as far through the development as concept design and a feasibility study/report (for final year project). I’ve now finished uni and as much as I’d love to see the Deakin team take what I’ve started and run with it – I just can’t see that happening… Deakin has been the smallest team at the Aust comp for the last 5 years or so and is really struggling to get enough interest from new students, I really hope they have a good comp and it would be awesome to see them score in all events but I fear that unless something changes, this may be the last year you see Deakin at comp for a while.

Back to my project though:
The things that are still missing from the design is the smaller details, such as bolt sizing, number and patterns. I’ve developed the casings with a 3 axis mill in mind and they could be lighter and hug the internals much better if cast like Auckland have done with their engine casing or if a machine with more than 3 axis were available. If I were to continue with the development I would run some more FEA and design the cases to double as stressed chassis members and so suspension mountings would be added to the gearbox cases. The front of the engine would bolt directly to the rest of the chassis. This means that main roll hoop bracing must run forward as there would be no main frame structure behind it, which is a bit of a pain (there are alternatives though). The triangular void mentioned by Z in earlier posts is not really that big but could easily be filled with the other 'nessesary ballast' associated with the engine, fuel tank, battery, oil tank, possibly a balance pipe for exhaust (if really needed, however twin exhausts running forwards with a carbon muffler each side would package nicely) The intake would probably be the hardest thing to get right as the inlet ports are facing away from each other and so a lot of effort would need to be put into an intake that flows nicely that does not have too much (or too little) volume to tune the two intake pulses to work with the restricter.

The engine and gearbox have been designed as separate units to simplify the oiling requirements and would allow a relativly quick change out of either engine or gearbox.

Engine:
The engine still needs oil galleries designed into it (the space is there though) and I propose a dry sump setup, again along the same lines as Auckland have done. (I’d like to note that I had done quite a lot of my design work before even becoming aware of what Auckland is doing – should I be worried that I may be starting to think like a Kiwi?…) The dry sump is really the only way I came up with of effectively scavenging the oil from the flat heads. Also needed is a very simple and short water gallery on one of the engine cases. The flywheel and windings from the donor engine have been incorporated and should provide plenty of power unless the team is doing something silly. The donor starter has also been used.

Gearbox:
A small internal oil pump would be required for the gearbox to circulate its own oil to keep the clutch cool, and feed the gears and bearings. Not too much oil capacity is required if done this way and any contamination from the clutch does not affect the quality of the engine oil (separate). The gearbox is very different to the Kiwi proposal and my goal has been to minimize any modifications to the donor parts. A Honda cam and pawl has been used for the diff, although I am of the opinion that an open diff be used and the rear brakes designed with a second pair of calipers with a micro controller looking after turn in, over steer and the like; taking info from the yaw sensor, steering angle and LR and RR wheel speeds. For the final reduction ratio from the output shaft to the diff, I looked at chain and sprocket, toothed belt, single gear reduction, and the only solution I found that would fit and still meet the strength requirements was a double reduction gear set. I'm not very happy with the result though, a more compact (and slightly more complicated) solution would be to use a planetary reduction, I've seen them used on front axles for 4WD tractors, presumably to lower the torque to allow smaller diameter CV's and shafts to be used, and they work very effectivly in that application. Quick change ratio's could still be made to work with that set up as well.

Custom Parts List is still fairly intimidating despite my best efforts to reduce it:
- Crankshaft
- Engine cases
- Dry sump setup
- Gearbox cases
- Spiral bevel gear set
- Double reduction gear set to diff
- Clutch cover
- Output shaft bearing caps (could be eliminated in favor of internal ring clips)
- Reduction gear set cover with clutch actuator mount.

I’m considering making the CAD files available to anyone who is keen to make the thing a reality? (on the provision they bring it to the Aust comp and I get a drive of it of course!!! haha.)

I now have ideas of starting over and repackaging parts from various donors to create an extremely lightweight (compared to what’s currently being used) off road package for a class that I could actually use it in! - Unlike FSAE. Anyways, I'm happy to talk more about it if anyone is interested.

(hope images aren't too big)
https://lh3.googleusercontent.com/-E7rkOPZcrqk/TtxZBuk8xMI/AAAAAAAAAA0/-SjEmDCUYxk/s912/full%252520assy%252520render%2525201.jpg
https://lh3.googleusercontent.com/-EOVFxtLHXF8/TtxY4p3sgvI/AAAAAAAAAAk/zkEsJcGyK0s/s912/engine.jpg
https://lh6.googleusercontent.com/-xMr0dz6T9aI/TtxY9s3fUNI/AAAAAAAAAAs/HLp6m7MbpXk/s720/gearbox.jpg

ZAMR

12-05-2011, 08:17 PM

Dazz, I've remember seeing this before and was impressed by the ambition and level of complexity, but this boxer design brings up another issue: yaw inertia of the engine itself.

While the CG is quite low, the specific yaw inertia is about as high as you can go with this boxer arrangement. One of the benefits of going to a single (or Ape, although the Ape is no longer popular amongst this crowd) is not only the weight advantage, but also the yaw inertia advantage. Your engine is the heaviest part of the car besides the driver and 4-cylinders spread that weight over a large xy-planar area, although not as widely as the proposed boxer. A single or v-twin has the weight concentrated in a more vertical fashion. As a thought experiment, place a 4-cyl on a frictionless disk and try rotating it in the z-axis with your arms and see how hard it is. Now try with a single. I've handled Aprilias quite a bit and am still amazed at how easy they are to rotate and move. I'd wager you reduce your yaw inertia by ~15% by switching to a smaller engine from a 4-cyl (anyone care to do the math?).

Edit: Just realized where the output to the wheels is. So theoretically you can squish the driver in closer and reduce overall inertia. This would probably make up for the layout?

Jan_Dressler

12-06-2011, 01:16 AM

Hi dazz,
nice! I really like this... But:

Originally posted by dazz:
Engine:
The engine still needs oil galleries designed into it (the space is there though) and I propose a dry sump setup, again along the same lines as Auckland have done.
"The space is there".. Brings back horror... Believe me, the space will not be there - not enough. Been there, done that. Take a look at this very raw pre-topology optimization model. It took me ages to get all the oil lines past all the other things (retaining most of the features of the Honda engine's original pressure oil circuit). And no, certainly not all the internal features of the model are highlighted.
http://www.fotos-hochladen.net/uploads/proe20bohrungby26sw5ij8.jpg

12-06-2011, 04:48 AM

dazz,

Great work! Shame that you won't be able to see it bear fruit. It seems that the biggest problem for some FSAE teams is the lack of any continuity of design philosophy. New team members come with their own ideas, and the "baby gets thrown out with the bathwater". http://fsae.com/groupee_common/emoticons/icon_frown.gif

Anyway, your package would fit perfectly in the sort of car I have been promoting here. The driver's feet on, or behind, the front axle. All major masses packed close to the CG and low down. Plus a smooth running flat-twin with equally spaced intake pulses. It has a lot going for it...

In fact, ...
given that there are about 400 teams worldwide ...
there might be a good business case to build, oh ... say...
about a dozen of them???

That's just to dip your toe in the water...
Then with about $1-2k profit each, based on cheap student slave labour doing the machining, etc. ...
that should cover the cost of the rest of the car...

Up to the school though, I guess???

Z

DougMilliken

12-06-2011, 08:06 AM

Originally posted by dazz:
I got as far through the development as concept design and a feasibility study/report (for final year project).

Whenever I see small boxer engines, I'm reminded of the Lotus microlite airplane engine. Monobloc construction--only split at the crank line, output drive combined with the cam drive--1/2 engine speed for slower turning propeller, many other unique & lightweight features. Some pics here, http://stargazer2006.online.fr...craft/microlight.htm (http://stargazer2006.online.fr/aircraft/microlight.htm) Prototypes ran, but it was never fully developed for proper aircraft reliability. I believe the original concept was by Tony Rudd, but others contributed.

dazz

12-06-2011, 05:20 PM

Originally posted by Jan_Dressler:
Hi dazz,
"The space is there".. Brings back horror... Believe me, the space will not be there - not enough. Been there, done that. "snip"

The SV isn't as bad as the Honda looks to be:

- Gearbox needs a supply to the centre of input and output shafts and to a spray rail, all from the same side of the case, and quite close to each other.

- Engine needs supply to the two main bearings (crank big ends are fed from these also), 2 piston cooling jets, and a single supply to each head.

- A multistage dry sump pump built into the bottom of the engine cases opposite the starter motor would scavenge the crank case, and the left and right heads, probably via external lines.

I'm not saying it's a 5 min job, I would have already done it if that was the case, and I reckon that there's probably a similar amount of time required to what I've already put into the project to work out all the small details.

For reference, the SV manual is pretty nicely detailed as you can see below.

https://lh6.googleusercontent.com/-09ov09Tib6c/Tt6tacGWFQI/AAAAAAAAABQ/8WGNBOP5h_s/s512/front-cyl.JPG
https://lh5.googleusercontent.com/-tDeHiVXPM_g/Tt6tdBtqJdI/AAAAAAAAABY/XG8RHaDvgF8/s512/rear-cyl.JPG
https://lh5.googleusercontent.com/-41tERNmlxjo/Tt6tWQMNiCI/AAAAAAAAABI/b-Fuxa4Pibw/s512/flowchart.JPG

nowhere fast

12-07-2011, 08:39 AM

I’m going back to Z’s essay 1 here.

I agree that the packaging of motorcycle engines is less than ideal, but wasn’t sold on the idea of building custom crankcases to reduce yaw inertia. I wasn’t convinced that the performance gains from increased yaw acceleration would be worth the extra effort over using an off the shelf engine. My reasoning was that high yaw accelerations occur for only a small percentage of an autocross lap; so how important can yaw acceleration be?

I started to think of simple ways to simulate the effect of improving yaw acceleration. The main difficulty is that increasing or decreasing yaw acceleration alters the path a car will take through a corner. A car with reduced yaw acceleration capability will need to begin turning in earlier on the straight, and travel on a tighter radius at the apex to compensate for the slower turn in. Since this car is traveling on a tighter radius at the apex; it must take the corner at a slower speed to remain within its lateral acceleration limits. Trying to calculate the line a car will take corner by corner through a lap sim is pretty complex; so I tried to think of a simpler alternative.

I came up with the idea of simulating a slalom with some simplifying assumptions: constant velocity through the slalom, and constant yaw acceleration followed by constant lateral acceleration once the lateral acceleration limit is reached. The reason for choosing the slalom is that this is arguably the section of track where yaw acceleration will be most important, and the line taken by the car is easier to calculate since there are some simplifying symmetries.

An object travelling at constant velocity and undergoing constant yaw acceleration will trace a spiral path; the radius of curvature will be ever decreasing and the path will soon curl back on itself. Surprisingly; a numerical ODE solver isn’t required to find the endpoints of the spiral segment, although some of the simulation calculation steps need a numerical root finding method. From here it is a case of solving the calculations and geometry to get a working simulation with lateral acceleration, yaw acceleration, and track as inputs. All up, I probably spent almost as much time writing this dribble as I did getting the sim running.

Here’s a plot of the lines taken by two cars with different yaw acceleration and all else (track, lateral acceleration) equal:
http://farm8.staticflickr.com/7009/6471717763_422cc6a83d_b.jpg (http://www.flickr.com/photos/67284757@N06/6471717763/)
Red represents the cones, blue is high yaw acceleration, green is low yaw acceleration, x’s represent the change from constant yaw acceleration to constant lateral acceleration. I used a large difference in yaw accelerations to exaggerate the difference in the paths taken.

Now I needed to figure out a typical range of values for yaw acceleration. I dug out some old data from our 2008 car, unfortunately my team didn’t have a yaw rate sensor so I calculated yaw acceleration from rpm (for some reason wheel speeds weren’t logged at this test) and lateral acceleration. This is probably the least accurate way to find yaw acceleration, short of rolling a dice. To make matters worse; the logging rate for acceleration was only 10Hz at this particular test. All these issues combined make the resulting yaw acceleration trace pretty much useless.

Simulation Results:
The simulation results are inconclusive because I can’t narrow down a range for yaw acceleration. If I use a yaw acceleration value at the high end of what I think it might be; a sensitivity analysis shows that lateral acceleration is significantly more important than yaw acceleration. If I use a value from the low end; the sensitivity analysis suggests that some of the ideas from this thread may actually give worthwhile gains.

This sensitivity analysis looks purely at performance parameters (lateral acceleration, yaw acceleration, and track) without considering what design parameters would be needed to achieve this performance. As a result there won’t be peaks in the slalom time results since increasing performance will always reduce the time taken through the slalom. Track is a performance parameter in this simulation since it only changes how straight the line taken through the slalom is without altering the lateral or yaw acceleration. Changing track in this simulation is equivalent to offsetting the slalom cones laterally without altering the car.

A sensitivity analysis of these parameters doesn’t tell the full story. The other thing to consider is how easy it is to improve these performance parameters. Track is easily changed; but in reality will affect lateral and yaw acceleration. As Z points out; reducing yaw inertia has a first order effect on yaw acceleration, while reducing mass has only a second order effect on lateral acceleration for a non-aero car.

Summing up: oddball engine packages might give worthwhile gains; or maybe not. As you were.

ZAMR

12-07-2011, 11:37 AM

Originally posted by nowhere fast

Summing up: oddball engine packages might give worthwhile gains; or maybe not. As you were.

I lol'd. What was the change in radius of curvature from one setup to the other? And then what was the change in velocity?

I reckon most simple laptime sims don't take into account yaw inertia, but then again they take a simplified approach to the track map that makes the car artificially slower around the course (eg. a constant radius path leading to a straight is slower than an increasing radius path). The decisions the driver makes arguably effects laptimes more than anything, and having a car that responds very quickly to change in steering input will probably go around a track much faster than a lethargic car would, even if simulations show little difference. I think the best way to do this would be to drive the car with ballast in the driver's lap, then again with ballast on the nose and tail. Then you can make a sure-fire decision as to whether inertia is an important factor to consider.

12-07-2011, 08:20 PM

Nathan,

Good work! That is exactly the sort of analysis all the new teams should be doing, rather than "what is design your car, respond urgently..." (with added spelnig mistakes). As you noted, it takes similar time to do the analysis, as it does to write it up.
~~~~~o0o~~~~~

Qualitatively, the gain from low yaw inertia is visible in Nathan's graph, at least as applied to the slalom. The high inertia (green) car must take a tighter radius turn near the cones, so will be slower. The big question is how much?

I think one "number" all teams should have for their cars is the "Radius of Gyration in Yaw". (Does anybody want to share theirs?) Combined with wheelbase (in a crude bicycle model way), this gives a non-dimensional parameter Ca = 2*RG(yaw)/WB, being the "Coefficient of Agility". I just made that name and definition up, but it is a good indicator of how quickly the car can change direction (smaller is better).

"Ca" is the ratio of the yawing resistance (proportional to the length of the dumb-bell) to the yawing control force (proportional to WB). Note that the maximum practical range for "normal" vehicles is about 1/2 to 2/1. A 200kg total mass car with "point mass" wheel assemblies of 10kg each, on a 1.2m x 1.6m rectangle, and ALL the remaining 160kg mass at a point at the centre, is equivalent to a dumb-bell ~0.9m long, for Ca=~0.56.

At the other extreme is a short wheelbase, lightweight farm tractor with fully loaded front-end loader and rear carry-all. Thus with most of the mass at the extremities. This can approach Ca=~2 (ie. dumb-bell twice as long as WB) and makes for very leisurely driving. You have to turn the wheel a long way before the corner, and then patiently wait for the nose to gradually come around...http://fsae.com/groupee_common/emoticons/icon_smile.gif

I think the best way to experience these differences in FSAE is as ZAMR suggested. A certain quantity of ballast (eg. barbell weights, say 50kg), mounted either under the CG, or split between the extreme nose and tail of the car. Then time yourselves through a slalom, and extrapolate backwards to see how a lower yaw inertia car would perform.

I also think that while low yaw inertia is mainly good for slaloms and chicanes, it also makes the car easier to drive in unpredictable situations, such as traffic, or for an inexperienced driver who might come out of a corner "pointing slightly the wrong way". The high Ca example above requires the driver to plan well ahead. If not, then the only alternative is to brake hard and hope you hit something soft...

Z

mech5496

12-08-2011, 03:08 AM

Sensitivity analysis, yes, OK, good for comparison but talking absolute numbers, does it make any difference at all? I believe that an easy-to-drive and predictable car can do much much better than a (theoretically) faster car which has "spooky" handling. That happens all the time in professional racing series, as there are numerous examples of drivers doing better laptimes with (again theoretically) lower-grip set-ups, because the car is easier to drive or better suited to their driving style. Now add the factor that FSAE drivers (ours at least) are nowhere near pros... My point is that from a pure design point of view, sensitivity analysis IS the way to go, but for real-life....hmmm, not so sure! For real-life comparison I would go with the ballast test Z mentioned. Anyway I'd personally prefer a car tested for 2 months than a car 0.5sec faster per lap and 2 weeks of testing...

Originally posted by Z:
If not, then the only alternative is to brake hard and hope you hit something soft...

Z

The famous "oh fuck" moment....http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

DougMilliken

12-08-2011, 10:14 AM

Originally posted by Z:
I think one "number" all teams should have for their cars is the "Radius of Gyration in Yaw".
Olley and others started looking at transient response in yaw in the 1930's and discussed it in his Notes. We include it in "Chassis Design" as Section 4.7 "Moment of Inertia and Wheelbase", page 247-253.
The lowercase "k" is radius of gyration (a distance). Rather than use the total wheelbase, the simple model is based on the front and rear portions of the wheelbase, "a" and "b". The nondimensional figure of merit is k^2/ab.
http://books.sae.org/book-r-206

12-09-2011, 12:51 AM

Doug,

Yes, and "k-squared-a-b" is even more commonly used in pitch mode analysis (ie. ride comfort - Rowell and Guest papers, 1920s, which are also covered in "Chassis Design"). Over the years I have kept coming back to the "dumb-bell to wheelbase" ratio as being more visually intuitive. It is roughly the square root of k^2/ab, so not much difference. (Incidentally, I think point "P" in Figure 4.24 of C.Dsgn is in the wrong place.)
~~~~~o0o~~~~~

Now for some quantitative analysis.

Based on countless assumptions, gross simplifications, etc., etc., I reckon lowering yaw inertia gives a 1 minute advantage in Endurance! http://fsae.com/groupee_common/emoticons/icon_smile.gif Well, roughly... All other things equal... This worked out in the margin of the TV times, late last night... You decide...
~~~

Consider a car with wheelbase Wb, mass M with 50% F:R, yaw radius of gyration Kz (so Ca=2.Kz/Wb), tyre coefficient of friction Cf, and gravitational acceleration G (racing is slower on the moon). The maximum horizontal force that front or rear tyre pairs can exert is;

Ff,r = (M/2).G.Cf ........... (1).
~~~

Now look at Nathan's curves and consider mainly the section from X=-3 to X=0 (with X-axis along centreline of cones).

At X=-3 the car is moving to the right and in steady-state "circular" cornering. So both front and rear wheels have a lateral road-to-wheel force to the car's right (ie. downwards in pic). These forces converge near the turn centre, somewhere on a vertical line below X=-3 (neglecting Ackermann, slip-angle drag, etc.). So picture a series of different radius arcs (ie. paths of the car's CG) with their centres on this line (below X=-3) and tangent to (-3,1). Maximum velocity the car can travel along these arcs of radius R is,

V = Sqrt(G.Cf.R) ............ (2).
~~~

Somewhere between X=-3 and 0 the circular right-hand-turn phase ends, and the car transitions towards straight-ahead (at X=0), and then on to the circular left-turn (near X=3). This requires a change from clockwise yaw velocity W (omega, in radians/second) at X=~-3, to same magnitude but anti-clockwise W at X=~+3. Therefore, this phase is a period of yaw acceleration dW/dt. Picture this "S-shaped" transition phase as simply a straight line tangent to the circular arcs and passing through (0,0).

Big question - what is the yaw couple applied to the car during this transition phase?

Let's assume that coming out of the "circular" phase the driver instantly turns the steering and front wheels to the left. The front centripetal force thus disappears, but the rear centripetal force remains at maximum. Conveniently, at X=0 the rear force disappears, and the front force suddenly rises to maximum, but now leftward for the turn around the next cone.

Of course, the forces would vary differently, and there is "tyre relaxation length" to consider, etc. But this simplification means we have a nice constant yaw acceleration given by;

dW/dt = G.Cf/(Wb.Ca^2) .......... (3).

(From dW/dt=T/I, and T=F.Wb/2, I=M.K^2, so dW/dt=(M/2).G.Cf.Wb/(2.M.K^2), etc.)

This yaw acceleration (Eqn. 3) is half the maximum possible, so I figure it is a reasonable guess. (Note, maximum is if both the front and rear wheels push laterally with max force, but in opposite directions.)
~~~

Now, to get a feeling for the numbers, let's draw a table of these potential yaw accelerations for different grip tyres. The Cf=0.5 is for wet road, and Cf=3 is for an aero car, where downforce = more grip. Assume Wb=1.6m and G=10m/s.s.

Ca=1 ("long" dumb-bell with same length as wheelbase).
------------------------------------------------------
Cf...... =..... 0.5..... 1.5..... 3.0
dW/dt =..... 3.1..... 9.4... 18.8 (rad/s.s)

Ca=0.8 ("shorter" dumb-bell 80% as long as wheelbase).
---------------------------------------------------------
Cf...... =...... 0.5..... 1.5..... 3.0
dW/dt =...... 4.9... 14.6... 29.3 (rad/s.s)

So, the short dumb-bell car is quite a bit more agile (faster turning) because of "Ca-squared".
~~~

(Deep breath, we're almost there...)

Now we sketch a number of different radius steady-state corners, and draw the tangents to these through (0,0). This way we can estimate, by scaling, the transition distances S (quicker than using trigonometry). Note S/2 is half this distance, only up to (0,0). We now figure out how much constant dW/dt is needed for the transition. Some algebra (based on W in the corner, then this dropping to zero in the time taken to go S/2, etc...) gives;

dW/dt = G.Cf/(S/2) ............ (4).

And since equations (3) and (4) are equal (for a perfect driver), we get;

S = 2.Wb.Ca^2 ...........(5).

Again, just to check that this is making sense, we draw up some tables. Conveniently, a 3/4/5 triangle gives us a maximum radius R=5m, which requires infinite dW/dt for the transition S of zero length. Shorter radii give longer transitions.

Cf = 0.5, wet road.
-----------------------
R....... =..... 2........ 4........... 4.5......... 4.8......... 5.......... (m)
S/2.... =..... 2.4..... 1.45...... 1.1......... 0.75....... 0.......... (m)
V....... =.... 3.16.... 4.47..... 4.74....... 4.90....... 5.......... (m/s)
dW/dt =.... 2.06.... 3.45..... 4.55....... 6.67...... inf!....... (rad/s.s)

Cf=1.5, normal.
-----------------------
R....... =..... 2........ 4........... 4.5......... 4.8......... 5.......... (m)
S/2.... =..... 2.4..... 1.45...... 1.1......... 0.75....... 0.......... (m)
V....... =.... 5.48.... 7.75..... 8.22....... 8.49....... 8.66..... (m/s)
dW/dt =.... 6.17.... 10.3..... 13.6....... 20.0..... inf!....... (rad/s.s)

Cf=3.0, +aero downforce.
--------------------------------
R....... =..... 2........ 4........... 4.5......... 4.8......... 5.......... (m)
S/2.... =..... 2.4..... 1.45...... 1.1......... 0.75....... 0.......... (m)
V....... =.... 7.75.... 11.0..... 11.6....... 12.0....... 12.3.... (m/s)
dW/dt =.... 12.4.... 20.7..... 27.3....... 40.0..... inf!....... (rad/s.s)
~~~

Finally, we come to some conclusions;

1. Corner radii and transition lengths are only a function of Wb and Ca (for this particular slalom, see Eqn. 5). The long dumb-bell car (Ca=1) has a transition distance of S=3.2m, so has to turn a corner of R=~3.7m. The shorter dumb-bell car (Ca=0.8) can transition in only S=2.0m, so can turn a larger corner of R=~4.6m.

2. Corner speed (which is the "constant speed" through the slalom) is a function of R and Cf. So with the normal tyres of Cf=1.5, the long dumb-bell car travels at V=7.4m/s (27kph), and the shorter, more agile car at V=8.3m/s (30kph). The higher the grip (Cf), the greater the speed differential.

3. If we now assume that this 3kph speed differential applies for the whole Endurance (because the car is faster onto the straight, needs less braking for the next slalom, perhaps a bigger speed differential at hairpins, etc, etc, etc...), then if the long dumb-bell car takes 30minutes for its 22km, for an average of 44kph, the shorter dumb-bell car should average 47kph, and take only 28.1 minutes.

This, after conservative rounding, to cover all those wild assumptions, gives a 1 minute advantage! QED. http://fsae.com/groupee_common/emoticons/icon_biggrin.gif
~~~~~o0o~~~~~

Corrections welcome (I doubt that I calculated/copied all those numbers right.....).

Z

PS. Anyone want to share how big their, err, dumb-bell is? That is, does your fancy CAE gizmology give a figure for your car's Yaw radius of gyration, Kz, complete with wheels and driver?

Crispy

12-09-2011, 05:34 AM

Originally posted by Z:
PS. Anyone want to share how big their, err, dumb-bell is? That is, does your fancy CAE gizmology give a figure for your car's Yaw radius of gyration, Kz, complete with wheels and driver?

I'll throw out some numbers for our 2011 car that I have a medium level of confidence in. Both the driver and the aero are on the heavy side, but both are quite quick as well http://fsae.com/groupee_common/emoticons/icon_smile.gif

Mass: 260 w/90 kg driver (235 kg w/o aero)
Wheelbase: 1.555 m
Rear Weight: 53%

MOI about Z:
Sprung mass 80 kg m^2 (60 kg m^2 w/o aero)
Unsprung mass 30 kg m^2
Total 110 kg m^2 (90 kg m^2 w/o aero)

Radius of Gyration: 0.65m (0.62m w/o aero)

Z's Ca Factor: 0.84 (0.80 w/o aero)

Milliken's k^2/ab factor: 0.70 (0.63 w/o aero)
or (k^2/ab)^(1/2) factor: 0.84 (0.80 w/o aero)

flavorPacket

12-09-2011, 10:17 AM

My last fsae car:
I_zz: 92 kgm^2 (measured on a rig at an OEM)
k: .587
Ca: 0.74

The current car I work on:
I_zz: 3500+ kgm^2 http://fsae.com/groupee_common/emoticons/icon_eek.gif
Ca: 0.91

Z, one thing I see missing here is the connection of these 'architectural' parameters back to the driver. One could make 2 cars with identical k^2/ab feel totally different with simple steering and tire changes. Including cornering stiffness normalized by steering ratio or some other metric will better project how the car will 'feel'. As Mr. Milliken writes, the linearized gains of sideslip angle, lat accel, and yaw rate vs steering angle can be quite valuable in developing a framework for fundamental vehicle architecture.

12-09-2011, 06:51 PM

Both above cars are quite compact/agile, with Ca=0.84 & 0.74.

I think the last time production cars had Ca>1.0 was in the 1960's with some of the US "land yachts". Many pre-WWII cars, with front beam-axles necessarily in front of engine and little rear overhang, had Ca=~0.7 (k^2/ab=0.5).

So, can anyone beat the current FSAE record of Ca=0.74??? http://fsae.com/groupee_common/emoticons/icon_smile.gif
~~~~~o0o~~~~~

Ryan,

My feeling for these MoI effects developed way back when I was driving various very high Ca (=~2) "farm" vehicles, often on low grip surfaces like wet clay. This high-Ca, low-Cf meant that everything happened very slowly, so it was easy to watch and think about all the dynamics going on.

For example, turn the wheel for 45 degree slip-angle, then wait and watch as the front tyres gradually bring the nose around. Interestingly, while this is happening the rear tyres are pushing outwards! Obvious when you think about it (both pairs of wheels between the dumb-bell half masses). But probably overlooked if everything is happening too quickly, like on a high Cf racetrack.

You say "One could make 2 cars with identical k^2/ab feel totally different...". True, but you can make any two identical cars feel different by, say, letting the air out of one car's tyres. What I don't think is possible is to make a high Ca car feel agile. It is a bit like trying to teach an elephant to dance.
~~~~~o0o~~~~~

(Edit.) Using the same calcs as my above post, a Ca=0.6 car (probably the lower limit) would be 0.9kph faster than the Ca=0.8 car. So only about a half-minute faster over Endurance (law of diminishing returns).

However, adding a lot of front and rear overhung aero might be costly. Going up to Ca=1.2 makes the car 6kph slower than Ca=1.0, or ~2-4 minutes slower. The aero downforce might overcome that, or not???

Z

ZAMR

12-09-2011, 07:48 PM

It should if it's well designed. A downforce package on an FSAE car should be light and produce a lot of downforce at low speeds. One of the parameters we used to define our wing performance was the "break even speed" or the speed at which you create enough DF (hence greater available yaw forces) to overcome the added inertia of the wings. For our car we estimated it to be ~25mph, 30 if being conservative, which is the low end of the track speeds. However we were only able to accomplish this because of a very lightweight, high DF package. Heavier, less aggressive wings will not "break even" until higher speeds.

nowhere fast

12-09-2011, 11:28 PM

ZAMR,
At first I was hesitant to post numbers since I would rather teams make the effort to do this type of analysis for themselves. Although thinking about it now, quoting a number from a forum to a design judge without any work to back it up wouldn’t go down well. I tried to drop enough hints in my post that teams could start on creating a sim like mine, but without giving it all away. The biggest hint is that an fsae slalom is not the only application of this particular spiral curve, the most difficult parts of the math can be easily found online if you know what you’re looking for. For this sim; figure out what type of spiral you’re dealing with and you’re halfway there. Z’s method of simplifying the transient period to a straight line is even easier and not unreasonable since the length of the transient section is inversely proportional to yaw acceleration.

Harry,
Good point about the benefits of driveability and testing time. Ironically, sensitivity analysis can help prove your point. If a simple analysis like this shows that your car should score within say 10 points of the winner, but at the competition you end up hundreds of points behind the winner; then you know that the performance of your car is not what’s holding you back. This can help put into perspective the importance of issues like driveability, testing time, manufacturing time, project management etc.

Z,
I ran some of your numbers through my sim, the results are pretty similar. I used 9.8 m/s.s for g, I just realised you used 10 m/s.s which accounts for some of the difference. t is the time taken to travel from X=0 to X=3.

Cf=0.5, v=4.78 m/s, t=0.671 s, R=4.67 m, dW/dt=3.45 rad/s.s

Cf=1.5, v=8.28 m/s, t=0.388 s, R=4.67 m, dW/dt =10.3 rad/s.s

Cf=3, v=11.71 m/s, t=0.274 s, R=4.67 m, dW/dt =20.7 rad/s.s

12-10-2011, 05:37 AM

Originally posted by nowhere fast:
I tried to drop enough hints in my post...
The biggest hint is that an fsae slalom is not the only application of this particular spiral curve...
Nathan,

So I'm guessing that Leonhard must have been a horny bastard, because a horn is spiral shaped, and in Latin is "cornu". Except that Fred was a Frenchman??? On the other hand, in Greek mythology the Fate that was the "spinner" of the thread of life was Clotho. http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

Z

nowhere fast

12-10-2011, 05:56 PM

Yep. http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

mech5496

02-02-2012, 02:56 AM

http://fahrzeugtechnik.fh-joan...-Joanneum-Racing.pdf (http://fahrzeugtechnik.fh-joanneum.at/workshops/2011-2012/2011-12-07-Joanneum-Racing.pdf)

Take a look at that...It seems like a neat little engine, developed by AMG Mercedes, Joanneum Graz and KA-RaceIng. Basics: 2cyl, 596ccm, 75kW, direct fuel injection, endurance consumption < 3,5l, integrated differential, first competition Formula Student UK 2012!

Wonder why this is not a "lean-rearwards cylinder" type of engine though....it seems that it could be built to package really neatly with integrated engine-chassis mounts etc. with a little more effort. Nevertheless it looks fantastic, cannot wait to see it in action! Any news from the other anticipated custom engines on FSAE? (Aucklands' and Brookes')?

murpia

02-02-2012, 06:09 AM

Originally posted by mech5496:
http://fahrzeugtechnik.fh-joan...-Joanneum-Racing.pdf (http://fahrzeugtechnik.fh-joanneum.at/workshops/2011-2012/2011-12-07-Joanneum-Racing.pdf)

Take a look at that...It seems like a neat little engine, developed by AMG Mercedes, Joanneum Graz and KA-RaceIng. Basics: 2cyl, 596ccm, 75kW, direct fuel injection, endurance consumption < 3,5l, integrated differential, first competition Formula Student UK 2012!

Wonder why this is not a "lean-rearwards cylinder" type of engine though....it seems that it could be built to package really neatly with integrated engine-chassis mounts etc. with a little more effort. Nevertheless it looks fantastic, cannot wait to see it in action! Any news from the other anticipated custom engines on FSAE? (Aucklands' and Brookes')?
Finally someone integrates a gear drive to diff in a transaxle setup...

But then doesn't integrate suspension pickups!

Regards, Ian

mech5496

02-02-2012, 06:14 AM

Ian, that might be because the engine is developed by 2 teams with AMG. Having suspension pickups (and chassis mounts) integrated, basically means that both teams will share rear halves of the car....

SoonerJack

02-02-2012, 07:06 AM

If I heard the guys from Karlsruhe right, they have more torque than basically anything ever seen in a combustion FSAE car. In every driving situation...

If it works as promised, it probably will be a great thing to watch!

Mbirt

02-02-2012, 09:32 PM

OBR engine specs are on the wall poster in this pic, but the resolution is just low enough that you can't read it http://fsae.com/groupee_common/emoticons/icon_frown.gif

http://a6.sphotos.ak.fbcdn.net...979_1332684962_n.jpg (http://a6.sphotos.ak.fbcdn.net/hphotos-ak-ash4/429007_314624675247935_152099461500458_914979_1332 684962_n.jpg)

Fantomas

02-03-2012, 01:26 AM

It will also be interesting to see, how the AMG teams do in design, since this will determine, if AMG did their work and just gave them a plug & play solution or if the teams really designed the motor on their own and just used resources provided by AMG.
I think this approach is very interesting on one side, but also very difficult to judge who did the real work on the other side.

Fantomas

SoonerJack

02-03-2012, 03:16 AM

Well, even if they did only little work on the engine (as far as I know, there are a lot of Karlsruhe students at AMG to do they degree thesis) then they aren't "worse" than any other team which is using a standard bike engine.

Sure they wouldn't get credit for the engine but so far there aren't many teams out there who did it and would crush them in the Design event.

They probably are getting a really nice engine, that's what counts.

There are some Electric cars with own motors of course but that's another level I guess...

murpia

02-03-2012, 06:13 AM

Originally posted by mech5496:
Ian, that might be because the engine is developed by 2 teams with AMG. Having suspension pickups (and chassis mounts) integrated, basically means that both teams will share rear halves of the car....
I agree that forcing an exact suspension geometry onto a team might be too much, but I see no evidence of ANY load-bearing mounts on those pictures. In mainstream motorsport it's normal for a tranaxle from Hewland, Xtrac, Ricardo etc. to have load-bearing mounts for dampers, rockers and suspension links. The rocker geometry & the exact design of wishbone clevises will be up to the chassis supplier, so they still have control of the suspension geometry, within the boundaries set up by the load-paths through the structure of the transaxle.

I still think this is a missed opportunity, as it appears to be an entirely un-stressed engine & transaxle, so the teams have to duplicate structure uneccesarily. I'd like to have seen a twin cylinder version of this:

http://dot.etec.wwu.edu/fsae/v30/v30pics.html

Regards, Ian

02-04-2012, 05:20 AM

Originally posted by mech5496:
http://fahrzeugtechnik.fh-joan...-Joanneum-Racing.pdf (http://fahrzeugtechnik.fh-joanneum.at/workshops/2011-2012/2011-12-07-Joanneum-Racing.pdf)
Two comments:

1. On page 21 is a decision matrix justifying the choice of a Line-2 engine over some alternatives (L1, V2, & F2). Interestingly the single (L1) wins almost every category except for "Leistung" (Power?). The L2 gets maximum of 25 points here, while the single gets 0 (!), so just misses out.

This seems a bit odd, given my earlier example of the 1970s Can-Am Porsche 917 with its air-cooled turbo'ed flat-12 that delivered 125hp from EACH of its 450cc cylinders. (Seems like some "creative" decision matrixing here... http://fsae.com/groupee_common/emoticons/icon_smile.gif.)

2. On page 44 is the Zugkraftdiagramm (Tractive Force Diagram?). To me, this shows the irrelevance of a multi-speed gearbox when you have a reasonably powerful engine.

Z

Bemo

02-04-2012, 05:58 AM

Just want to through in that the AMG engine isn't running until now as far as I know. All numbers are results of simulations.
There has been quite a similar project in the past - remember the Mahle engine? We in Stuttgart do. I don't wish anybody bad luck, but I'm more than sceptic. People in big companies very often think that it can't be that hard to build something which is far better as anything else in a competition where just stupid students take part in.
We also were part of the team choosing process and there were a couple of points which led to the decision that our team won't seriously apply for the project. The real reason for turbocharging is, that the new AMGs will all be turbocharged...

As said - my personal opinion. Prove me wrong.

Mbirt

02-04-2012, 09:27 AM

Is anyone else having trouble downloading the pdf? I talked to KIT at FSAE-MI about the engine and would really like to know more. If it's small enough to attach to an email, could someone shoot it my way? It would be much appreciated.

I wouldn't mind comparing it to the Mahle development presentation I recently found in our office http://fsae.com/groupee_common/emoticons/icon_cool.gif

mech5496

02-04-2012, 10:37 AM

You got pm.

AxelRipper

02-04-2012, 08:33 PM

While discussing this new AMG engine earlier in out garage, myself and another team member got to thinking. How does this work per rule B8.7.1

B8.7.1 Turbochargers or superchargers are allowed if the competition team designs the application. Engines that have been designed for and originally come equipped with a turbocharger are not allowed to compete with the turbo installed.

This engine has clearly been designed with a turbocharger.

whiltebeitel

02-05-2012, 02:31 AM

To be honest, the intent of that rule (IMO) is to prevent a team from buying a canned engine that will easily outperform everyone else without really understanding the system they are using.

There are few teams that know as much about turbocharging in FSAE cars as the Joanneum Graz team. They know what they are doing, and they more that likely did quite a bit of engineering with the AMG guys over their system, especially since it looks similar to the layouts they have run in the past.

Mbirt

02-05-2012, 09:41 AM

Originally posted by whiltebeitel:
There are few teams that know as much about turbocharging in FSAE cars as the Joanneum Graz team. They know what they are doing, and they more that likely did quite a bit of engineering with the AMG guys over their system, especially since it looks similar to the layouts they have run in the past. Which makes it even more baffling that the single-cylinder concept received zero points for power on their decision matrix. The matrix shows that the single-cylinder was the clear winner.

For those who are better with the German language: in their comparison which shows the 360 degree firing order to make more power than the 180/540 degree firing order, did they expand the intake plenum (intercooler tank) volume to compensate for the uneven firing order? I would not have expected the difference in power to be that great, but trying to minimize intake plenum volume would do that. The Rotax 600 ACE 180 degree parallel twin revs to 7500 rpm without balance shafts and its rotating assembly would have been my first choice for this project.

ed_pratt

02-06-2012, 03:24 AM

Originally posted by Mbirt:
Is anyone else having trouble downloading the pdf?

Yeah, for some reason I can't open it here either. I thought it was because I was on a university computer, but couldn't open it a home either.

Could someone possibly mail it to me?

Thanks,

Ed

shark.ashwa

02-06-2012, 05:25 AM

ed.....you got PM...

Sharath

mk e

02-06-2012, 05:48 AM

I’ve been working as a new product development engineer for about 15 years now and I can tell you that the subject of how exactly to choose feature objectively is the subject of quite a bit of debate at all levels of the 3 places I’ve done this job.

The company I work for is all about the 6 sigma methods these days and my black belt project was finding a way to use a DOE in a double blind customer preference study so we could figure out just WTF the customer actually wants because when you just ask them they lie. They don’t lie intentionally, but they tell you what they think the right answer is, or what they try to do instead of what they actually do and that leads to putting the wrong features into the product…..and getting the product wrong isn’t tolerated well where I currently work, we are #1 in our market segment and intend to stay #1 http://fsae.com/groupee_common/emoticons/icon_smile.gif

Anyway, there are a lot of pages with a lot of good ideas in this thread but it comment caught my eye as a problem.

Originally posted by Z:

1...... The L2 gets maximum of 25 points here, while the single gets 0 (!), so just misses out.

Generally, with whatever tool you create for ranking, a 0 in any category that was important enough to be on the list should lead to an automatic rejection of the concept…..but a zero shouldn’t have been given there either. It’s easy to create a comparison matrix, then use it as a tool to justify a decision you’ve already made in our mind and it appears that is what was done here.

Scaling is really hard. What I find normally works best is a log or exponential scale of some kind. I like stuff the is 1-10 so for say power, a 1 might be enough hp to get the car through the events….maybe 3-5hp, something that gets you in the game is a 5, say 45hp?, a 7 would be a hp number that is truly competitive, 65hp maybe?, 8 = 70hp, 9 = 85hp, 10 for anything over say 75 because that is about the practical limit and more just spins the tires anyway. The goal is always to get resolution in the area of interest. If the goal is also excellence than another rule that says on certain key issues a score under 5 or 6 or 7 is a veto for the concept.

This is how I do it, hope the ideas are helpful.

ed_pratt

02-06-2012, 06:30 AM

Thanks for the forward.
Ed

Bemo

02-06-2012, 07:59 AM

Originally posted by Mbirt:
Which makes it even more baffling that the single-cylinder concept received zero points for power on their decision matrix. The matrix shows that the single-cylinder was the clear winner.

That's the point of these decision matrices. By playing with the numbers you will get any answer you want. I already mentioned that from the beginning AMG insisted on turbocharging...

I can't find the document anymore. If you send it to me, I can translate the part you mentioned.

mk e

02-06-2012, 08:31 AM

Originally posted by Bemo:

That's the point of these decision matrices. By playing with the numbers you will get any answer you want. I already mentioned that from the beginning AMG insisted on turbocharging...

That is ALWAYS the problem with this type of exercise. There is simply no such thing as an “unbiased” opinion or rating.

The first pass at any model of anything will have the biases of the person who created it build into it which is why the validation of the model is so important……an unvalidated model is just the opinion of the person who created the model, nothing more. It looks like more because there is math in it…… but it’s all based on assumptions and until a validation is performed you have absolutely no way of know if the assumptions are correct or not or whether the model is complete or not.

Validations suck to do, there is no other way to put it, they absolutely suck….but without a validation you have nothing. You don’t have a useable engine selection matrix, you don’t have a test method that you can use to make decisions, you have nothing but a guess.

Bemo

02-06-2012, 12:09 PM

Originally posted by Mbirt:

For those who are better with the German language: in their comparison which shows the 360 degree firing order to make more power than the 180/540 degree firing order, did they expand the intake plenum (intercooler tank) volume to compensate for the uneven firing order? I would not have expected the difference in power to be that great, but trying to minimize intake plenum volume would do that.

In the whole document there is no word about the intake plenum. I don't know what the original intent of the document was, so I don't want to judge, but it doesn't go very deep and a lot of assumptions aren't explained at all.
But I wouldn't tell everything in public either http://fsae.com/groupee_common/emoticons/icon_biggrin.gif.

TMichaels

02-07-2012, 01:37 AM

Hey Guys,
would anyone care to forward me the pdf as well?

EPMPaul

02-07-2012, 05:03 PM

Originally posted by TMichaels:
Hey Guys,
would anyone care to forward me the pdf as well?

+1

mk e

02-09-2012, 08:53 AM

I was at a meeting yesterday that was all senior people at a really conservative and very successful company that literally STARTED with finger pointing and screaming and that went on for an hour and a half…..probably the single worst meeting I’ve ever been at. The subject was customer requirements, design inputs and ranking design concepts.

It’s not just FSAE teams that struggle with this stuff.

mdavis

02-09-2012, 10:02 AM

Can someone forward me the .pdf as well?

Bemo

02-10-2012, 03:25 AM

You can download it here (remove the spaces):

h t t p : / / dl . dropbox.com / u / 41503869 / Joanneum-Racing_2cyl_motordesign.pdf

mdavis

02-10-2012, 10:58 AM

Thanks Bemo. When I tried the previous link, it said I didn't have access to the server, no matter which computer I used.

Rex Chan

02-19-2012, 10:31 AM

Does anyone know what kind of oil system the Jawa engine uses? I read the manual, but it's kind of vague. I suppose what I'm really asking is that will the stock system work in an FSAE car? The bikes seem to run pretty upright under sideways "cornering"...

Or do the frquent rebuilds take car of any poor oiling?

02-20-2012, 11:45 PM

Originally posted by Rex Chan:
Does anyone know what kind of oil system the Jawa engine uses?
Rex,

I'm also only going from their web info, but I see essentially an all-roller-bearing engine with a dry sump.

Roller bearings only need a fine mist of oil to lubricate their cages. Nevertheless, the Jawa uses a positive displacement pump (probably at low pressure) to send oil to the crank bearings. From there the piston gets the spray (no oil-squirters for piston cooling, 'cos the methanol does that). Likewise, the cam runs in needle bearings, so probably manages just with the mist.

The interesting part is the return from the crankcase to the oil reservoir (built into right side crankcase). It seems this is via the pumping action of the piston, similar to a two-stroke, with reed-valves ensuring a one-way flow(???).

Corrections welcome. http://fsae.com/groupee_common/emoticons/icon_smile.gif

Z

Chapo

02-21-2012, 02:57 AM

If it is a problem Rex grab ya self an accusump, they work pretty damn well at signifigantly reducing/ removing oil surge problems from lateral G force on a bike engine (even with a really small sump like the ADFA teams). Just plum it in to the system after the pump and your good to go...

Having said that though the dry sump should help a bit on the Jawa.

Rex Chan

02-21-2012, 05:51 AM

They are all methods to solve oil pressure problems, but will add weight/complexity.

The attraction of the Jawa engine to me is the lack of auxiliary systems it would need: air cooled = no radiator (maybe a mechanical fan); internal oil system; carby = no fuel pump. The only issue is the lack of a starter: either a starter motor (needs total loss crank battery, no alternator), or air start (compressed air)?

Adambomb

02-21-2012, 02:52 PM

For starting we've had several "outside the box" ideas. However I'd say they are all so impractical I don't really feel like I'm "spilling the beans" http://fsae.com/groupee_common/emoticons/icon_wink.gif

1. Kick start lever extended into cockpit via linkage. This would work great until the engine kicked back, shattering your knee cap against the front roll hoop.
2. Pull start rope tied to steering wheel. Just release the quick connect and give the steering wheel a few quick yanks! This could prove difficult...
3. Latest idea, and probably my favorite: Not sure how this would fall in line with the "no hybrids" rule, but use pedal-start like on old-timey motorbikes! Just pedal it up to about 5 -10 mph and dump the clutch! Not only that, but if you blow your engine up you could still pedal the car across the finish line!

Lorenzo Pessa

02-22-2012, 03:23 AM

Originally posted by Adambomb:
3. Latest idea, and probably my favorite: Not sure how this would fall in line with the "no hybrids" rule, but use pedal-start like on old-timey motorbikes! Just pedal it up to about 5 -10 mph and dump the clutch! Not only that, but if you blow your engine up you could still pedal the car across the finish line!

http://en.wikipedia.org/wiki/Piaggio_Ciao
We can ask Piaggio if they have some spare parts.

Series One

12-08-2012, 06:53 AM

On the subject of objectively choosing an engine, how much consideration should be given to engine availability specifically to satisfy the production targets as presented in the Business Presentation?

My question is prompted by the realisation that it is relatively easy to source a wide variety of suitable current and obsolete engines in ones and twos from salvage yards but when it comes to buying brand new complete 'crate' engines, the field narrows drastically. Is it reasonable to base a business model on second hand engines, either factory fitted or customer sourced?

If not, and the model should be based on the assumption of a reliable source of new engines, does that source have to exist in the 'real world' or can it be make believe, like the business model itself?

Warpspeed

12-08-2012, 05:02 PM

I suppose you could argue the case that this is a very limited production, built to order "race vehicle" not a volume produced World Car.

So your business plan might be for a quite limited production volume, and if there is a readily available supply (secondhand) of a particular engine in your particular country, why not ?

This is not really a fake reason either. Developing or super tuning a cheap and plentiful mass produced production engine for many classes of motor racing has been going on for a very long time.

Colin Chapman originally used whatever engines he could get his hands on cheap to put into his Lotus race cars. He won a lot of races, and his business model was good enough to keep going for a very long time.

Series One

12-08-2012, 06:34 PM

Ta. I assumed that to be the case... but it wouldn't be the first time an assumption has come back and bitten me in the arse.

AxelRipper

12-09-2012, 09:07 AM

Well it wouldn't be the first time someone used an "obsolete" engine for racing either. Look at Formula Ford and Formula Vee. While FF is updating a bit, the Kent motor people still use hasn't been sold in the US in probably 30+ years, and FVee or its relative Formula First isn't updating really at all and still using VW Type 1 parts.

mech5496

09-12-2013, 05:53 AM

Another back from the dead thread, but I did a readthrough again and I came across an old post of mine...

So, what makes the best package?
1)High enough torque
2)CVT
3)Low yaw inertia/components near the CG
4)Low CG
5)4WD?

The correct answer?! IMO build a 4WD electric car, with inboard motors and halfshafts both front and rear (keep unsprung masses low that is, maybe moving the brakes inboard as well). Having 4 motors and power limitation at 85kW, those can be lightweight (10-12kg per motor) and based on their inherit high torque output they can directly drive a halfshaft each, so no need for gearboxes an CVT's. Plus you can have 4w torque vectoring based on accelerometers, yaw rate sensors, speed and steering angle...Plus due to really good packaging possibilities of the batteries you can have a low-yaw-inertia car with a low CG. Plus you will have much better efficiency than a combustion car... Weight for the complete powertrain could be at 80-85kg, some 20kg heavier than a 4pot combustion powertrain, but not having in mind components like intake, exhaust, fuel tank, differential, differential mounts, chain etc. The only downside I see on that is the cost, as batteries, motors etc should be really expensive. Boring race cars?!

http://www.youtube.com/user/DU...#p/a/u/0/x8-dj4eDCAM (http://www.youtube.com/user/DUTtwelve#p/a/u/0/x8-dj4eDCAM)

Do not think so...

Now add an aero-pack on that and lots of testing and go smoke everybody in the competition! I must admit it sounds easy...:P

Well done KIT-e for building my dream FSAE car! :P

06-21-2014, 12:06 AM

One of my sons has recently been bitten by the "VW-Bug" bug. While looking around at aftermarket stuff I came across the following "Scat" pages.

VW-engine rebuild kits: http://www.scatvw.com/master/engine_kits/

Scat Split-Port heads: http://www.scatvw.com/master/cyl_heads/split_port.shtml

The Split-Port heads immediately suggested themselves as a good starting point for a really neat little FSAE single-cylinder engine (or see PS below).

For those of you who do NOT believe that the "optimal" FSAE engine must have ~16 cylinders, or at the very least have 4 or 5 valves per cylinder, and be water-cooled, and come from a racing motorcycle, and have a built-in 6-speed sequential gearbox +++, please read on. :)

The above web-pages suggest you can buy, off-the-shelf, many of the key parts for 4 single-cylinder engines for about $2k total. So ~$500 gets you about half the parts for a single-cylinder engine.

The other parts needed are;
* A single-throw crank (I suggest about 80 mm stroke).
* A small crankcase (in two halves, with the split perpendicular to cylinder bore, like the VW).
* A short camshaft (mounted in the block near cylinder mounting face, for short pushrods).
* Small oil pump(s) (maybe 2x, giving dry-sump + pressure lube, with dry-sump tank being part of crankcase).
* Possible balance-shaft(s) (2x, counter-rotating to crank, for primary balance only).
* Starter-motor and air-cooling-fan (taken off small single-cylinder "industrial" engine, as used on water-pumps, generators, etc.).
* Alternator (optional, but smallest belt-driven type would do).
* Intake and exhaust plumbing, and EFI, and cooling shrouds, etc. (similar to work done on most typical FSAE engines).

I would do it "laid-down" style, so it looks like the right-rear cylinder of the standard VW flat-four. It would fit in the car as a lateral-crank, reverse-rotating single. The heavier crankshaft end would tuck under the driver's back for minimum yaw-inertia. The cylinder would point backwards with spark-plug and valves under the diff for easy access.

Driveline to the diff would be a clutch and two-stage chain+gear reduction, to get the engine RPM down to wheel RPM, and rotation in the right direction. At most, a two-speed + neutral gearbox could be incorporated into the gear reduction, probably in-unit with the diff. Jawa make a compact two-speed clutch-gearbox that could be suitably modified. Alternately, a belt-CVT going from the crank back to a gear reduction at the diff. Or else a really neat IVT that I have in mind!
~o0o~

The key advantage of this engine layout is that it gives an extremely compact package by FSAE standards. The driver can sit entirely within the wheelbase (ie. feet behind front-axle line) giving minimum yaw-inertia. The laid-down engine gives minimum CG height. The very simple engine helps give minimum total mass. The slim-line package, with NO RADIATOR sticking out in the wind, helps with minimum aero-drag, and minimum interruption of aero flows to low set rear wings (where they should be).

"Yeah but, ..." say all the testosterone overdosed young boys, "... WHAT ABOUT HORSEPOWER!!!"

Well, yes, the design is based on a 70+ year old, as-cheap-as-possible, peasant's car...

"Ughhh, it's an air-cooled, push-rodded, 2-parallel-valved, wedge-head! Aaarrrghhh... YOU'VE GOT TO BE KIDDING!!!"

Nope. :)

IMO, choosing the right bore and stroke for about 600cc (see Scat pages, or others, for all the available bores) would give a quite easy, naturally-aspirated, 60 crank hp. This is half the maximum ~120 hp available through the 20 mm restrictor (or 19 mm for the preferable E85), and has proven to be more than enough to win major recent FSAE comps (check the history!).

Furthermore, I am aware of quite a few racing turbocharged VW-flat-fours of under 2.4 litres in Oz that make well into the 300s, and often 400+ horsepower, depending on who you believe. These cars race in series that require considerably more engine longevity than the ~1 hour of tootling around an FSAE track. I have no doubts that 100+ hp would be possible from the above type of turboed, ~500+ cc "VW-Scat-Single". With sufficient development, and maybe a new V-valved, shallow hemi-head, the full ~120 hp should be possible. If you really wanted it.

Best of all, should a Team get this design sorted out, and if they then ramp up production of the cranks and crankcases (possibly having them made in China?), then I could see a tidy profit from assembling and selling these singles.

How much would your Team pay for a very compact, lightweight, no-radiator, "perfect fit for FSAE", engine that makes a reliable 60 hp N/A, or ~100 hp turboed? And especially one that has all the "might-need-replacing" parts readily available off-the-shelf?

Z

(PS. Instead of using the Scat Split-Port heads, a common practice is to simply hack-saw a standard VW cylinder-head in half. There are many You-tube videos showing all sorts of aeroplane engines, such as flat-twins and multi-cylinder-radials, built in this way...)