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Well, nothing stops you, or other teams for having a separate "noise" tune/engine map.
Also the RPM defined by piston speed means that whatever happens at speeds higher than the tested ones, is "fair game".
Well, with a turbo, you might even set your competition rev limiter lower than the noise test RPM.... But still fail noise.
And remember all the dbA, dbC noise filtering stuff. Did you have the correct setting at your db Meter?
Since there is this talk of acceleration staging advantage and teams not sharing information....
https://lh5.googleusercontent....taging+Advantage.jpg
Effect of staging distance on acceleration run time for constant 1 G acceleration
Pretty easy to whip up an excel sheet for yourself to play with if you are curious.
While the same is true for the previous record times (conditions unknown), that and the clearly higher grip of the surface are reasons why our team never bashed around about having "world record times". Even though we were aware that our times were the fastest at the time in both acceleration and skidpad (and both have later been beaten by Budapest and Monash respectively).Quote:
Originally posted by TMichaels:
I have to admit though that the FSG way of staging is not rules compliant...
Maybe the radius at skidpad was not right... Jokes aside. I only wanted to point out that the achieved times can not necessarily be directly compared due to several factors (track going downhill, staging with more distance to the starting line, track being too short) influencing them.
Which is why I am always careful with stating something about world's quickest whatever run, etc.
From marketing point of view we should have done some bashing around to get publicity... But that's another story, it's not our style and we don't want to be one of the teams making egotistical claims.
However now someone called for the fastest time ever and I felt I should share it along with a bit of history what's happened after the previous fastest time.
Raises and interesting dilemma:Quote:
If Guinness wasn't there, it didn't happen ;-)
You know that Greenteam Stuttgart is the Guinness world record holder and you've seen Delft in FSG. Which one would you think is the fastest in the world? http://fsae.com/groupee_common/emoticons/icon_razz.gif
PS. Getting a bit off track here but does Guinness records have restrictions on the surface they're driven? Just wondering because all 0-100km/h etc WR's are highly sensitive to the environment.
I gotta say, I was not expecting that much difference in time for a few feet of staging difference, good catch.
All this talk of surfaces, it would be interesting to see what a FSAE car would do on a prepared surface like an actual drag strip. Anyone who's gone drag racing before, will attest to the surface at the starting line being very tacky; to the point of removing sandals and other loose fitting shoes.
Anyone willing to fess up to trying it?
You don't see any safety issue with running over 2.5 the maximum straight line distance FSAE cars should run? In close proximity to catch fences and guard rails?Quote:
Originally posted by rjwoods77:
Bracket racing for money at the local 1/8th mile drag strip would make for a fun way to raise funds and gain sponsorship through generation of local interest if it can be done safely. Jr Drag wrinkle wall tires for 10" wheels are available and you could even do bigs and skinnys for the full effect. Talk to the event promoter and get bye runs only so there isn't a safety issue running side by side with a full size vehicle.
Have at him boys.
Removed prior post and response. Detracted from thread.
In Rob's defense, just because the strip is 1/8 mile long doesn't mean the driver needs to do full 1/8mile runs. I believe there is a timing loop at 60ft and 330ft if the team intends to do multiple runs with changes, plus using on board data acquisition.
I certainly would agree going to the drag strip would generate a lot of interest and a lot of smart (and not so smart) people that could give you opinions and ideas, as well as possible leads for sponsorship on machine work, and cheap parts. Seems like a reasonable proposition for a test/tune night at the local strip.
That said, who knows if the drag strip would let you run, I think when I took a mini-sprint to the drag strip a few times the wheelbase was questioned, but the safety equipment was decent so they let me run. And if the school is providing insurance for the team/car, you'll have to clear it, better off asking permission rather than ask forgiveness on that one.
When I took the mini-sprint, lots of people stopped by to check it out because it was 'different', and I got a lead on FJ1200 parts (that was the engine in it).
In reality it is even more sensitive to staging due to the fact that acceleration is, ideally, at its maximum at the beginning and not constant over the entire run.Quote:
I gotta say, I was not expecting that much difference in time for a few feet of staging difference, good catch.
You can gain about 0.1s in acceleration with the "correct" nose shape, if you tailor it to the lightbarrier setup. Of course only, if the staging is done rules compliant.
Makes it a bit difficult as trap height is not defined in the rules and might change from comp to comp.
But for FSG staging you might be able to gain that 0.1s by using an "underhanging" nose design to nicely match the low trap height and then use a suspension setup that results in enough pitch angle to get over the trap. http://fsae.com/groupee_common/emoticons/icon_wink.gif
I guess we need to build a stand for the lightbarriers which randomly adjusts it height after each run http://fsae.com/groupee_common/emoticons/icon_smile.gif
For Formula events, the main thing is that at any one competition, the starter at the Acceleration event MUST make sure that all the cars line up the same way. Comparing the times from one event to another is just an exercise - as others have said, there are too many variables to make it worth expending the effort.
However, if you guys keep on flogging this one, and start trying to duck under (or over) the light beam at the start, the Rules Committee will probably be forced to require a "flag" on the front of the car like the MSA mandate for hill climbs.
As far as consistency in accel staging is concerned. A few years ago (2010 maybe?) the acceleration stagger actually had a tool(a few 2x4's nailed together) and a painted line on the ground to line each car up so that the nose of each car would be lined up very close to each other from car to car. But for whatever reason they only did it at the one competition and I have never seen it any where else in the world.
I guess you are talking about this scene:
http://media.formulastudent.de/FSG10...almonat-X3.jpg
We used this from 2006 to 2011.
In 2012 we switched to a triple light barrier setup, which is more accurate and controls a kind of traffic light to show the stager whether the car has to be moved further forwards, backwards or if it is perfectly staged already.
The light features three bright LED lamps: red, green, red.
See this picture (the lights are above the big grey box):
http://media.formulastudent.de/FSG12...7_grams-X2.jpg
If the left red light is on, it means the car has to be pushed forward towards the starting line. If the middle green light is on, it means, the car is perfectly staged. If the right red light is on, it means that the car is too close to the starting line and has to be pushed backwards.
A quite convenient and accurate way of staging, transparent for the driver and taking into account the different shapes of the noses due to using light barriers at the same height as the timing system.
I know I am late on the topic but a few people wondered why ETS didn't make the finals in design at MIS. Here what we've got as a review :
- Looking unprofessionnal with a design board that was falling to pieces... they got a point here
- Being 3 minutes late... they got a point here too
- Communication : the team didn't deliver the information smoothly (hummmmm, we felt the same)
- Improvement : the juges were expecting that "we take more risks" and they felt like they were expecting a 110% improvement where we only delivered 102%. They called it the "price of fame" lol.
Our opinions have been given to the right persons already. I don't feel like I need to say more. I don't know for the rest but top 3 was definitly very deserving teams. Congrats to GFR, from a dynamicist point of wiew you guys are the best.
It just felt a bit frustrating finishing 3 points away from 2nd place and less than 20 points from 1st ! Again it is racing and OMG please keep it so competitive ! Stuttgart, Talinn and Akron are all very good teams. It is a shame that we didn't get to see Ann Arbour, Maryland, S&T, McGill (well not long enough for these guys), RIT and GFR finish endurance.
Phil Arscott was so good to see out there ! My dad saw the video on GFR's FB page and told me I had more work to do lol
Xavier,
Thanks for your post. The first three points explain a lot. The judges are particularly harsh on teams turning up late to their allocated design times. The same things kept UWA out of design finals in 2007 (or 2006) Michigan. It is much easier to accept if you think of it as the same as turning up late for your endurance run and earning a 2 minute penalty. It might be a good idea to ammend the rules to have definite late penalty applied to late appearance to static events. At least it keeps it transparent, and maybe that penalty should be applied post final score as it would be for endurance. I don't think there would be an objection by the teams who understand that these events need to run to a tight schedule.
The improvement issue is a tough one. We are generally told not to think in terms of "delta" to last year's vehicle. This is tough as most good teams work on long term improvement and the big conceptual years cannot occur every year. To do so would be bad design and resource allocation. Having been in design finals a few times I am also aware that you tend to talk about where you are going with the project in the future. The judges do not forget this and if you fail to meet your objectives they remember. In Oz we were told of a team that was planning to meet this target and do certain things with their car. In listening it was obvious the judge was talking about you guys, so there is a certain amount of "fame" and expectation built around some teams.
Having been involved with the rise of two teams I think the expectations of the team by the judges end up too harsh during this period. You can have meteoric improvement over a short period, but as you do so the learning curve for new team members gets much harder. The fact that in one year the team improved 50% and in the next improved only 10% is not an indication of a lesser team or poorer design process. This is very hard to grasp when you are used to thinking of a company or team largely made up of the same people year in year out. This problem is compounded when the judges generally only see the few long term team members in the judging tent and miss the fact that half of the team has changed.
Otherwise your example adds evidence to a few points I observed in design events:
- Appearance of both the car and the team is worth much more than you can imagine. As much as judges are trying to be objective it is very hard to undo a first impression (either a positive or a negative one). Carroll Smith told us that one.
- Confidence and delivery can be more important than the content you are delivering.
- Every team member should be able to give a concise 1-2 min summary of the goals and main features of the car (covering the same points). This avoids mixed messages to the judging team. We used to practice this on other teams and spectators whenever they came to look at the car.
- The judges may say they are not interested in "delta" or a comparison to your old car, but you need to be very ready to show what has been changed and best of all have some nice brand new stuff (i.e. not just improved) to show them. This can be process or simulation related if it is a really unique approach. Sometimes what people say they want is not what they want at all, rather it is what they want people to think they want. Confusing, but true, and assuming the judges are human it applies to them as well.
I am not sure whether these points should be necessary to do well in an event based on the design process and achievements, and the first three reek of marketing vs. engineering, but they helped make sure that our team never finished outside the top 2 in design for the last 3 years I was a student (3 wins, 2 second places).
Kev
It was 3 minutes before (not late) actually. They probably wouldn't have noticed it if our design board didn't let us down, but it definitely did give a pretty bad first impression.
Apart from that, we had the same design team that won this event at FSG last August, with more to say and more to show.
So you weren't early enough?
I would hope you weren't judged too harshly on the basis of a design board. The car and your team should be more important than a few posters.
I would love for their to be some public (and anonymous) feedback mechanism for the static events. This could help highlight why some of these scores are occurring so all teams can learn. At the moment team members are reluctant to talk about gripes or issues with the worry it may adversely affect their results in future events.
As it stands we are no closer to understanding why ETS got equal 10th/42nd in design with one of the best dynamic cars at comp, with a team that usually does very well in design, with a car that was definitely different and better to previous vehicles.
Kev
Kevin,
Regarding your push for "transparency" and "feedback" at the Michigan event:
+ I was the lead judge for my 1st round queue, and my judging team did a 20-30 minute feedback session with every team we judged. Giving this feedback is the responsibility of every design judging team in Michigan and, honestly, a part of the judging duties that I really enjoy.
+ Our feedback sessions talk specifically about the team's car and give suggestions on how to improve. I will usually mention the kinds of things (generalizations) the top scoring teams know, can validate, considered, etc. We're always trying to teach students/teams. The feedback sessions are also a time for an interactive discussion between the students and the design judges. We often answer a lot of questions.
+ Note that there is a public design review of the top three cars every year.
+ All of a team's information is considered confidential, so don't expect any design judge to speak specifically to this discussion about ETS in public. While I did not judge ETS, all the design judges get together after the 1st round of judging to discuss/debate who makes finals. I heard the arguments, and I heard the reasons why the decision was made. ETS has received feedback (evidenced by Xavier's post).
+ I can't believe that "team members are reluctant to talk about gripes or issues with the worry it may adversely affect their results in future events". While I can't say that I've worked with every design judge at the Michigan event, I can tell you I have never seen any evidence of this happening.
Edward,
The feedback at the events to each team is already good at a lot of events and not what I am really getting at. I miss having a design finalist review such as done in Michigan. There hasn't been one in Australia for a very long time. In fact I think the feedback from the judges in most competitions to individual teams is pretty good, and I was probably not clear on this in my post.
Nor am I pushing for more transparency or feedback at the event. I wasn't there and I can't comment on how it occurred.
To clarify I think the following could help:
- FSAE / Student is truly an international event. It is one that hundreds of universities follow, and those away from an event are hanging on the release of results and why they occurred the way they did. The community is hungry for commentary on both the dynamic and static results. The times speak volumes for the dynamics, but without good transparent information about the static events (the design by far the most important) we have very little understanding of the reasons behind the scores.
- Film and post the design review to the comps. It really helps the international FSAE community to understand and support the events.
- Encourage students to provide constructive feedback to the community at large as to how they believe the event went. It would be great to hear the sorts of things that students discussed in the design event.
While I understand the reluctance to discuss individual team results, I think that some short public (i.e. forums, fstotal, blogs) stated reasons as to why there were some surprising results would inform the greater FSAE community. Informing one team and you educate 20 people, inform the community and you get your point across to thousands.
I personally want to know the story behind ETS' design score, because from the final scores it is one of the most interesting stories of the Michigan competition. GFR's endurance run was another and thanks to this topic we know the story behind that one.
There are a lot of fans and followers of FSAE around the world, and for an event that had 140 international Universities, thousands of students, millions of dollars, many different concepts, ideas and stories. All we have to sate our appetite until the next big comp is 9 pages of forum posts, a few youtube vids from teams, a scoresheet and some poorly updated twitter accounts.
Kev
Kevin,
Thanks for the clarification--makes sense. It's reassuring that you weren't trying to be a "conspiracy theorist" http://fsae.com/groupee_common/emoticons/icon_smile.gif
I try to follow the other events, too, from my side of the computer screen. One of the most interesting parts about being at a competition is hearing all the individual stories and sagas. I agree that these stories don't travel well to the larger Formula SAE/Student world.
I think you have some good ideas, especially filming and posting the design review of the top cars.
One point I'd like to comment on:
At the risk of sounding argumentative (which I'm not trying to be) I don't think the times explain the dynamic events any better than the scores explain the static events. For example, if there is a "surprising" result on skidpad I don't know why the car was slow unless I was there watching it, and even then I might not! Was the car difficult to drive (maybe because of kinematics, compliance or setup issues?), was the engine down on power (electrical glitch, wrong engine map?), was the driver inexperienced/tenative, error setting tire pressures, maybe a brief rain shower, etc.? I can raise the same kinds of questions about a surprising dynamic result as a surprising static result. The difference, of course, is that the static results are judging calls.Quote:
The times speak volumes for the dynamics, but without good transparent information about the static events (the design by far the most important) we have very little understanding of the reasons behind the scores.
The details matter (a lot!) for everyone's individual story. It would be difficult to bring all these out. There's also the problem of taking things out of context, which already happens way too much as students discuss their judging feedback.
So, while I agree that getting more info out would be interesting, there are certainly some practical difficulties. Perhaps there's a way to get more out there without setting-off a larger set of problems. I agree that this is worth thinking about.
And while I know you're talking about results, I'll note that the design judges (and a few people from the other static events) are as active as ever in reaching out to educate the students. In North America we have the Collegiate Road Show, last year we wrote "Learn & Compete", there are design event review videos online (I recall some by Pat Clarke at FSG a few years back) and some of the design judges even travel to individual schools during the year as a guest lecturer (myself included). Several judges contribute to these forums. If only these resources were available to me 20 years ago when I was a student!
Quote:
Originally posted by Kevin Hayward:
... in design events: ...
- Confidence and delivery can be more important than the content you are delivering.
As he usually does, I reckon Kevin has got it right.Quote:
Originally posted by Edward M. Kasprzak:
... Our feedback sessions talk specifically about the team's car and give suggestions on how to improve.
If the Design Judges are really giving the students useful feedback, as Edward suggests, then why is it NOT working?
Almost every other form of "motorsport", amateur or professional, always shows a steady improvement in performance, at least until the Rules are changed to slow the cars down. In FSAE the rate of improvement has been glacial, even though the aero rules have recently been freed up!
I am quite convinced that if there was an amateur drag-racing class with similar rules to FSAE (20mm restrictor, 75m distance, etc.), then over the last 20+ years the Acceleration times would have dropped to the low 3 seconds, possibly even high 2s. Likewise, Skid-Pad times should be in the 3 seconds by now. But instead the times have hardly changed (average times have probably increased, if you include Indian teams).
The problem, IMO, is the all too common attitude these days that "There are no wrong answers, just different choices...", or similar drivel. The oft-repeated DJ version of this is "We don't mind what design decisions the teams make, just as long as they can defend those decisions convincingly..." (see Kev's quote). Of course this is nonsense, and is probably why so many teams keep making the same wrong decisions.
Yes, some decisions are plain STUPID. A good example at this recent comp was the large number of cars with front pushrods leading to rockers and spring-dampers mounted ON TOP of the noses. Yep, rockers and spring-dampers mounted to give the highest possible CG, the maximum yaw inertia, and all that extra, though unnecessary, chassis tubing and bracketry up there.
Now I am sure that the teams adopt such bad designs because they see so many other teams doing same (ie. quite natural for H. Sapiens to follow the flock). Yet there is absolutely no valid justification for this sort of design. But do the DJs point out such bad decisions to the teams? Apparently not, because the teams keep repeating them.
~~~o0o~~~
Anyway, I reckon a better example of design feedback, and perhaps the way the Design event could go, is the "driver swap days" after the Australian events. Experienced team members drive the other teams' cars, and then publicly give very interesting and useful critiques of the cars, good or bad.
But until something like that starts happening, any team aiming to win outright had better look for a 100+ point jump on the opposition in the Dynamic events, just in case they are dudded in the Design tent.
Z
(PS. In the interests of openness and transparency, are we ever going to hear why UWA only got 3/200 Design points in FSAE-A 2012???)
I think the biggest problem with what you're saying is the glacial progress of the competition (other than the tires available and the skill of the drivers, but thats not my point) is the fact that unlike an amateur drag racing class, if you're lucky you can keep a core group of members going for 4 years in FSAE. Almost every year you've got someone (or a group of people) who are leaving the team who have hopefully lent their knowledge to the members still on the team to continue on. It doesn't matter how much you try to teach, it takes quite some time researching and learning to get to a certain level. A lot of times, when you realize that you're at the level where you have at least an understanding of a system on the car and how to solve the problems behind it, it is time for you to graduate. You can't teach most freshmen how to solve an 8 DOF tire model (random example). Or if you can, the chances of them truly understanding it and being able to build on it are slim to none.
In most other motorsports, you get AGES to continue developing things. Your chief engineer and technical specialist don't change every year, and with each leader a new goal for the car. And then, unless you see something break, you may repeat that mistake in the future, simply because you didn't know. Its the school of real world engineering, and you've only got 4 good years in this sport before you have to move on to something bigger (or grad school).
Axel,Quote:
Originally posted by AxelRipper:
I think the biggest problem [is]...
... you're lucky you can keep a core group of members going for 4 years in FSAE...
I agree. It seems that every few years the teams "reboot", and are back at square one.
An interesting thing is that many of the post-FSAEers on this Forum look at the problem from a much bigger-picture point of view (eg. Geoff and his "Reasoning..." thread), and, IMO at least, see the problem as being a lot easier to solve than when they first started. Namely, focus on the really important stuff, and keep everything else as simple as possible. By contrast, most newbs want everything as complicated as possible, because "Hey, we're building a mini-F1 car here!".
The disappointing thing is that FSAE is supposed to be an "educational competition". All these useful lessons should be passed on to each new intake of students. On the face of it, we should expect FSAE to have the fastest rate of improvement of all types of motorsport. Relatively liberal rules, hundreds of universities around the world, thousands of research theses each year, all with the singular goal of building "the fastest possible autocross car, ever!". But it ain't happening...
Honestly, I have to blame the Design event as being a major reason for this almost complete lack of progress. Too many newbs have (or are given?) the impression that their job is to impress the DJs with their "mini-F1" car...
Z
Well to be fair, doing things based on lesson learned is one thing, but new teams sometimes want to do things differently. Its their freedom and its their lessons to learn. Another thing different from the real world is that results don't necessarily translate directly to funds or lack of funds. Because the focus of this being a student competition, its again coming back to the question of winning or learning should come first....
Zee, did you ever wonder...
http://ct.fra.bz/ol/fz/sw/i55/5/6/22...ey--9085f4.jpg
Thank you for bringing such a brilliant example. You may be personally convinced that this is the case, but there are some very good reasons for having the dampers on top of the nose. The forces you introduce into the chassis can be massively reduced and you can get to extremely better spring rates, especially when using 10'' tires.Quote:
Originally posted by Z:
Yes, some decisions are plain STUPID. A good example at this recent comp was the large number of cars with front pushrods leading to rockers and spring-dampers mounted ON TOP of the noses. Yep, rockers and spring-dampers mounted to give the highest possible CG, the maximum yaw inertia, and all that extra, though unnecessary, chassis tubing and bracketry up there.
For me your sentence is definitely a zero-pointer. All the disadvantages of a push rod system you bring here are correct, but you miss some important advantages. The first five cars from our team had the push rods on top of the nose, then in 2011 the team decided to switch to a pull rod configuration. In 2012 this was kept as the moulds for the monocoque were reused. This year they switched back. Most people I know who tried both prefer the push rod configuration.
This has gone a bit off topic, but it is so great to show that sometimes it really isn't clear what's the right decision...
In addition to Bemo's points: I'm betting Z has never tried to package an electric motor in a 10" front wheel http://fsae.com/groupee_common/emoticons/icon_smile.gifQuote:
Originally posted by Z:
Yet there is absolutely no valid justification for this sort of design.
Bemo,Quote:
Originally posted by Bemo:
... The first five cars from our team had the push rods on top of the nose, then in 2011 the team decided to switch to a pull rod configuration. In 2012 this was kept as the moulds for the monocoque were reused. This year they switched back. Most people I know who tried both prefer the push rod configuration.
... sometimes it really isn't clear what's the right decision...
The disappointing thing here is that you seem to suggest that there are only TWO possible decisions. Namely, "Do we use push-rods, or pull-rods?"
This is especially disappointing given that this thread's originator, RobbyObby, has the signature quote,
"A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away." -Antoine de Saint-Exupery
YOU DO NOT NEED PUSH-RODS OR PULL-RODS, AT ALL!
In fact, I would say that the reason that there is so little progress in FSAE is that you are all wasting far too much time on such useless decisions.
~~~~~o0o~~~~~
To explain above, I earlier suggested FSAE Acceleration times should be in the low 3 seconds by now, and Skid-Pad times in the high 3 seconds (possibly lower for both). I mention these Dynamic events because they are the most objective, so times can be compared (AutoX and Enduro have changing layouts each year).
Anyway, some simple big-picture "decision making" suggests that you can get into the 3 seconds in Skid-Pad by building a simple, lightweight car, with as much aero downforce as you can find. Push or pull-rods are irrelevant (in fact, a disadvantage). Power-wise you only need about 10 kW. And it should be quite obvious that this sort of car (with a bit more power) will also do well in AutoX and Enduro.
In Acceleration, my numbers suggest a maximum power car (~90 kW at crank) with the usual FSAE weight distribution of ~50:50 can at best get into the ~3.8 second times. This confirmed by the results over the last 20 years. On the other hand, a simple lightweight car, with only about 50 kW at the crank, but with rear weight between 60% and 70%, and the right launch technique (the first 5-10 metres are the most important), will get into the ~3.5 second times.
Now good Acceleration times are not very important for overall FSAE results. But squashing the major masses (ie. driver and engine) backward to give ~60+% rear weight can also significantly lower yaw inertia, and that does give a big performance advantage overall.
So why do most current FSAE cars have 50:50 weight distribution, and also an unnecessarily large yaw inertia? Because, "Well, err..., that's what everybody else is doing...". It is nothing but mindless copying of the motor-bike-engine-with-forward-leaning-cylinders-that-pushes-driver-forward-and-over-the-front-wheels. Just like the mindless copying of push and pull-rods...
When are you students going to learn some engineering?
Z
Z,
A couple questions.
1) How much do two FSAE spring/damper units weigh?
2) How much do two human legs weigh?
3) How much more important is it to lower item (2) by one inch than it is to lower item (1) by one inch?
I agree that we could get into the low-fours on the skidpad if we were allowed a decent (wooden!) skirt on our tunnels. However, the FSAE rules state VERY clearly that nothing other than the tires may touch the ground.
Good luck designing the 65% rear weight distribution car, or finding two tires, one with twice the cornering stiffness of the other, that otherwise have identical cornering characteristics (not just the lateral vs vertical force functions but identical paths to operating temperature from cold). If you are anywhere near the minimum wheelbase, and are opposed to building a big heavy car with a big heavy four-banger engine, you will have to start with a "sidewinder" engine and its compromises and be very careful with your driveline part selection to get anything like 65% of the weight on the rear tires.
Charles,
Z has indicated a preference for direct mounted shocks instead of pullrods / pushrods. This allows for low legs and low shocks, as well as being a very simple light option. Motion ratios for a double a-arm would be in the region of 0.6 to 0.7 which isn't far off what a lot of teams run with the mountain bike shocks anyway.
Kev
Quote:
The disappointing thing is that FSAE is supposed to be an "educational competition". All these useful lessons should be passed on to each new intake of students. On the face of it, we should expect FSAE to have the fastest rate of improvement of all types of motorsport. Relatively liberal rules, hundreds of universities around the world, thousands of research theses each year, all with the singular goal of building "the fastest possible autocross car, ever!". But it ain't happening...
Honestly, I have to blame the Design event as being a major reason for this almost complete lack of progress. Too many newbs have (or are given?) the impression that their job is to impress the DJs with their "mini-F1" car...
I just want to address the negative view on the progress of this student design series:Quote:
When are you students going to learn some engineering?
http://sphotos-g.ak.fbcdn.net/hphoto...50078367_n.jpg
Not everyone is a genius, blessed by the Flying Spaghetti Monster with the Chapman touch to turn any car into a rolling puff of air. Not everyone is writing their PhD thesis on the "super advanced ultimate controls, make car go super fast system" that they are finishing up this term after dedicating 8 years of their life to FSAE.
This, as anything else in the world, has evolved, and has made its progress, both good and bad. Students are exploring different avenues, deriving their own formulas of how to tackle this problem. Is their a correct answer for how to tackle this? Probably not. Is it the one that wins? Sounds reasonable, but only if it still addresses the key point that this is a design competition meant to encourage teams to learn along the way. I feel that THAT is the most important aspect of this. It's like a big science fair for college kids, just bigger toys, and they actually get to play with them. If you insist that there is only one solution to solving this problem, then in your mind, there is only solution, but there have been many different winners and concepts that have come through this program, all with their trade offs. Want to criticize someone on putting a 1lb part half a meter in the air? go ahead, but I'd rather put the rest of the car closer to the ground under that 1lb part.
Not everyone is building an all out autocross car either. Sound ridiculous? Sure, it does. Why wouldn't you want to be the fastest? Because this is such a cumulative point event, it's more important to very well in all areas than be the team that only dominates 1 event.
This isn't life and death, have a little fun with it.
Fun fact that I should throw in based on the last couple posts. The 2007/2008 UB FSAE car used a Satchell Link solid axle with a pullrod and rocker arm connected to each birdcage...
http://www.eng.buffalo.edu/Stu...a_web/images/car.jpg
...and in two separate conversations with top tier design judges one of the very first things they both asked is why I didn't just tie in direct acting dampers off the birdcages and into the chassis. Looking back at it I could have done so and saved myself a bunch of grief in the design of the car.
Z, I appreciate your observation that FSAE cars are slow to develop but do you expect them to have a linear progression in performance? I would say performance is more likely to go asymptotic with unchanging rules.
Tires are the most important, and the limiting case here. I don't think you could come up with a purely theoretical FSAE car to run in the 3's in skidpad with the currently available tires. Even if you simulated a car with zero CG height and impossibly low overall weight. Aero is measurable, and would be even better on such a car, but it's a lot easier to calculate something than to implement it.
And likewise, tires and surface play a significant role in accel. I think much like your skidpad times, your 'analysis' is making a lot of assumptions here. First being power; 90KW is a ridiculous crank power level for a 20mm restrictor engine. How are you simulating "right launch technique"? What traction limit are you assuming for the cold tires. I don't doubt your assumptions gave you the results you calculate, but a 65% rear weight bias (with driver) 350lb car with 67HP is probably un-achievable.
I would agree though, that some teams and team members focus on unimportant details and ignore some fundamentals that would result in a faster car. But, I would say, that's part of the learning process. A lot of times, you can't dismiss an idea until you've allocated at least some resources to it, and even at the professional racing level, most ideas don't make it to the racetrack. It can sometimes seem like there are no good ideas, and other times there are so many reasonable ideas that limited resources have to be allocated based on other criteria.
I disagree with the idea that only out-of-the-box innovation will lead to learning how to be an engineer. You also shouldn't so easily dismiss the development of the current FSAE car, of close to 30 years now, to mindless 'monkey see monkey do'.
In summary, many quality engineers have gone through FSAE; you don't think one of them has thought about having higher rear weight bias, you think you are the only one in the world that thinks that might be an advantage, and none of them have thought it through and tried to implement it?? Be careful making the assumption that you are the smartest one in the room...
Well, it is bucketing down rain outside, so I may as well have another go at this... Also, with Michigan just over, some teams might now be thinking "How can we win next year?".
But firstly, the expression "mindless 'monkey see monkey do'..." is an insult to monkeys. Monkeys are very independent and perceptive thinkers. I have seen baboons regulary outsmart university educated H. Sapiens. It is we who should really call ourselves Homo Mimicus. But now I am getting off-topic...
I can understand that many of you students don't understand "The Theory". That is your teacher's fault. But all that I say below, and in most other posts, is based on "The Practice". All this can be found in the history of motorsport. I am sure that the average baboon would pick this stuff up after one day at a racetrack. Unfortunately, I guess you guys have to rely on Google, for which you have my sympathies... http://fsae.com/groupee_common/emoticons/icon_smile.gif
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ACCELERATION EVENT - As "engine and turbo guy" VFR750R should know, the maximum power that any restricted racing IC engine has ever made is about 40 hp or 30 kW per square centimetre restrictor area. So the maximum power you can hope to get in FSAE is about 90 kW (at the crank).
With 50:50 weight distribution, typical CG height, rear wheel drive, no aero, and a lightweight car, this 90 kW engine will spin the wheels almost all the way down the track (ie. traction limited all the way). With the typical tyres available these days, and a typical track surface, which give a typical Mu = ~1.5, this car will get ~3.8 second times. Most importantly, MORE POWER = NO BETTER!
The "right launch technique" I mentioned above (and as any baboon would tell you) is to get almost all the weight onto the driven wheels. So with RWD you want to be "popping a wheelie". Front-engined drag-cars do this by raising the CG, but this is not good if you also want to go fast around corners. So the obvious solution, as seen on by far the majority of racecars (ever !), is to have more rear weight, and bigger rear tyres.
For FSAE I suggest 60%R as a starting point. The general packaging layout to achieve this has been posted many times on these pages. Side-winder engines are NOT needed (where did that come from, Charles???). With this weight distribution and an average power FSAE engine, 3.5 seconds is reasonable. Geez, it is not that hard! http://fsae.com/groupee_common/emoticons/icon_smile.gif
For the Acceleration event itself, it may be beneficial to give your lightweight driver a "booster seat" (ie. like kiddies have, but intended to raise overall CG). Rear anti-squat also helps. To understand why the first ~10 metres are most important, draw a graph of car velocity (y-axis) vs time (x-axis). Acceleration is the slope of the curve, distance traveled is the area under it. (Hint: At any given time you get more area under the curve if the curve starts off steeply...)
VERY IMPORTANT! Longitudinal acceleration is not very important for overall points in FSAE. Much more important are lateral acceleration (see below), and yaw acceleration. You get greater yaw acceleration if the car has lesser yaw inertia. Squashing the driver and engine backwards (eg. for more rear weight) can lessen the whole package's yaw inertia.
Lateral and yaw acceleration are not dependent on engine power (to first approximation), but they have the greatest affect on overall points. Do the simulations and tests!!!!!
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SKID-PAD - No, VFR750R, "Tires are [NOT !] the most important...". In the hundred+ years since rubber tyres were first used in racing their maximum "coefficient of friction", or Mu, has increased from about 1, to about 2. These numbers correspond to attainable horizontal "Gs" of the car. A few years after racers discovered aero downforce the horizontal Gs doubled. Then a few years later they tripled, then quadrupled...
The practical limit for Gs due to aero is the driver passing out. This is never reached because the organising bodies keep changing the rules to restrict aero, and thus to restrict cornering Gs and speeds. (BTW, this is why aero on all current racecars is so inefficient (ie. high drag and low downforce), because it allows the cars to keep their noisy, high revving, high power, "sexy" engines, but still be slow and safe).
In 2002 Carroll Smith was encouraging more teams to go aero (Scott Wordley has a video linked somewhere). A few years ago the FSAE aero rules were freed up. But still very few cars are getting under 5 seconds in SP. Come on guys, take the hint. http://fsae.com/groupee_common/emoticons/icon_smile.gif
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PUSH & PULL-RODS - On the "Suspension Design" thread I recently listed the dozen or so excuses that are given for using these, and why those excuses are nonsense. The only excuse (I won't call it a reason) that was supported by other FSAEers had a defense that went something like this;
"If we are silly enough to buy really expensive dampers, and if we are silly enough to build really fragile wishbones, and if we are silly enough to crash this super-fragile car in testing, then we might save the cost of a new damper.....".
So, summarising this argument, if you are really stupid (I figure 3 x silly = 1 x stupid), then you only have to stupidly pay for your new wishbones... Err, or something lame like that...
Anyway, the really important point here is that no one gave a compelling argument as to how push/pull-rods make your car go faster. That is, push/pull-rods give (next to) NO PERFORMANCE ADVANTAGE AT ALL. (Well, in an indirect way they might help a bit with aero, but they are by no means necessary...)
Bottom line here (and in keeping with MCoach's post above), is that using "pushrods-to-springs-on-top-of-the-nose" is a lot like wearing your baseball cap backwards, and upside down, or whatever... I reckon you will have a lot more fun, and win a lot more, if you just learn to play baseball. http://fsae.com/groupee_common/emoticons/icon_smile.gif
Z
Look, I don't want to get into a pissing match of performance can's and cant's, but it's pretty obvious that not one team has ever achieved 90KW, and I know several teams that have had cylinder pressure tuned engines and all the bolt on electronic goodies one could ask for. Some of these engines have seen similar development as seen on professional racing efforts. No professional engine shop says "well an ALMS engine makes xHP/cm^2, so a cup restrictor engine should make XX-HP".
Your 30KW/cm^2 is by your own admission a guess, an assumption of what is achievable, based on another configuration of engine in another series. Can you verify the output of the engine that creates that claim; can you verify the engine was not leaking air to achieve it? It's fun to think about what-ifs, but when the highest verifiable output is in the range of 70KW, you think these engines are ~30% off their potential?? And I know of several professional applications that are highly developed and competitive that do not reach 30KW/cm^2.
This kind of activity is nothing more than a kid saying "why doesn't GM make a 2500HP car that makes 5000lbs of downforce, for $8000. GM is dumb for not doing it, I'd buy one.
And I'm actually getting a bit upset that you are insulting pretty much everyone in the series. Sure there are teams that get many of their designs by bench-marking others, and not every team is equal in abilities (and budgets), but you are claiming expertise over every area of the car, and critiquing a lot of work and accomplishments and trivializing the knowledge required to succeed.
I wonder, since you are such an expert, why didn't your teams' FSAE car get into the 3's in accel and skidpad, make 90KW, and make the driver pass out from all your downforce... I await your excuses about how you are only one man and if you had 30 of you on your team, it would have been easy to accomplish said goals.
Quote:
I wonder, since you are such an expert, why didn't your teams' FSAE car get into the 3's in accel and skidpad, make 90KW, and make the driver pass out from all your downforce
VFR750R,
Z has not been a participant in this competition nor a mentor for any team that I am aware of.
In fact, here is picture from the younger days:
http://fsae.com/eve/forums/a/t...010404621#5201040462
And a few articles he has written:
http://www.smithees-racetech.com.au/ackerman.html
http://www.slashdocs.com/yxurz...n-erik-zapletal.html
http://www.theoryinpracticeeng...ced%20suspension.pdf
Erik,
until we can talk in terms of compromise and structured thoughts, it makes it very difficult for anyone to take you seriously. Start treating people like colleagues and less like monkeys. While it may be on the limits of possible to reach these theoretical maximums that you've called reasonable, as I've mentioned, some of us have other goals in mind. We've made 60 hp (44.7 kW) to the wheel on our FSAE car from our 450cc motor. Assuming a 5% driveline loss, that's 104kW/L. Should we shoot for that magical 90kW/cm^2? No, to us the amount of fuel we need to carry nor an available motor to reach that is worth the weight they bring. I prefer the straw hat to a baseball cap anyway. http://fsae.com/groupee_common/emoticons/icon_smile.gif
90 kW is totally beyond the limit of what is achievable in FSAE. Comparing FSAE Engines to other restricted engines is more like comparing apples and oranges.
If you use a naturally aspirated engine you will need at least 4 cylinders for a rather constant air mass flow through the restrictor. However this results in very small cylinders which them self create increased thermodynamic and mechanical losses. A very high compression ratio without compromising the combustion chamber is also not possible due to the very small stroke.
Going for a turbocharged 2 cylinder engine will also not be able to yield 90 kWs because of the bad efficiency and high back pressure of the small turbochargers needed.
VFR750R,
You should really read what was written before getting your knickers in a knot.
So, for the third and last time;
1. "... the maximum power that any restricted racing IC engine has ever made is about 40 hp or 30 kW per square centimetre restrictor area."
In the next few months Ian Bamsey's "Race Engine Technology" magazine should have a wrap-up of this years Le Mans' engines. There he normally gives his well reasoned (IMO) estimates of their power. Typically, all these 5,000+km engines produce about 35hp/sq.cm. Engines requiring less durability have produced more. But the point is, 30 kW/sq.cm is about the UPPER LIMIT. Good engineers should know their limits... http://fsae.com/groupee_common/emoticons/icon_smile.gif
2. "...Most importantly, MORE POWER = NO BETTER!"
The whole point of my above two posts was to make clear that FSAEers should NOT be chasing more power. A medium power car with ~60+% rear weight will out-drag the top horsepower car with 50:50 weight distribution.
3. If you have well reasoned arguments as to why 50:50 weight is best for FSAE, then please share them. And while you are at it, you might let us know why the vast majority of rear-drive racing cars have got it wrong for all these years, by putting more weight, and fatter tyres, on their rear wheels.
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MCoach,
I like monkeys. They are a lot of fun. http://fsae.com/groupee_common/emoticons/icon_smile.gif
As above, I reckon the 60hp you are getting is more than enough to do well in FSAE. In a simple, lightweight car, with about 60% rear weight, and the right launch technique (front wheels almost lifting), you should be able to set a few Acceleration records. And that's always fun! More importantly, the rest of the package would be a good starting point to do well in the other Dynamic events. (Hint: just add that aero-undertray.)
BTW-1. That first car I built in your top link was simple, strong, had 50:50 weight distribution that gave great handling (on equal size tyres), and was all-round pretty good. Its weakest point was that it lit-up the rear tyres too easily! Every other RWD car I've built has had a lot more rear weight, which, all things considered, I reckon is better.
BTW-2. One of your other links managed to spell my name wrongly in three different ways! Now you know why I keep it simple here. http://fsae.com/groupee_common/emoti...on_biggrin.gif
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RenM,
I reckon a 20mm restricted, <610cc engine could get close to 90kW (at the crank, no accessories, etc.). But as before, I reckon that would be a pointless exercise in FSAE.
(Note that said engine, probably a single with big plenum and bespoke turbo, would have to have all bearing sizes minimised, oil/water pump flows minimised, 2-ring piston(s) with tiny skirts, gear drive to cams (?), CR on the edge of detonation, DLC everywhere, and quite a few other things. But the biggest influence on max power would be the fuel. Ie., use the one with highest energy release for a given amount of air breathed.)
Z
For simple curiousity, I wonder what the weight distribution of the current Le Mans Prototypes are...running basically now squared tire setup...
RM,
I am quite sure that there are LM cars nowadays that run close to 50:50 weight distribution. This is mainly due to the ACO mandating that only certain size tyres are allowed. Some teams choose to use the wider "rears" all around, so they have to set their weight distribution accordingly (the name Nick Wirth comes to mind?).
In F1, way back during the 1,000+hp turbo era, the tyre rules were much more liberal, and 70%-rear-weight with monster rear tyres (20" wide) was the norm. Tyrell even went the six-wheel route, with 4 x tiny 10" fronts (still available from Avon?). In the 1990s Max Moseley decided he didn't like this look, so for purely aesthetic reasons he imposed rules mandating a very close range of tyre sizes front and rear. The weight distribution had to follow and ended up around 55R:45F.
Whenever the rules are free, RWD racecars end up with more rear weight. A good current example is Bowlby's DeltaWing (built as a completely rules-free concept car), which I believe has at least 70% rear weight, maybe closer to 80%.
Z