Regenerative braking

[eirik]

After reading the 2013 Formula SAE rules I am still a little uncertain about the rules concerning kers. I am thinking of using an electric motor for regenerative braking together with an IC engine. I cannot find any rule that states it is prohibited but this rule (IC.1.1.1) makes me a little uncertain. It says:
"
The engine(s) used to power the car must be a piston engine(s) using a four-stroke primary heat cycle with a displacement not exceeding 610 cc per cycle. Hybrid powertrains, such as those using electric motors running off stored energy, are prohibited. Note: All waste/rejected heat from the primary heat cycle may be used. The method of conversion is not limited to the four-stroke cycle."

This rule says electric motors running of stored energy are prohibited but what if all the energy used in the electric motor is generated while braking the car during a race? Or does this rule forbid any use of kers combined with IC engines?
How do you think "stored energy" can be interpreted?

[AxelRipper]

Where are you going to put the energy that is generated by the regenerative braking before you use it in the electric motor? As far as I know, you have to store the energy from the regenerative braking before you can use it again. And with that, stored energy is prohibited.

There is a Formula Hybrid competition that allows for what you are describing, but FSAE/FS does not allow it.

[Racer-X]

I might be wrong here but my understanding is that you may not use batteries to drive an IC car. I believe KERS violates two rules. First being that you may not store energy in batteries to drive the car, and all the power must come from the engine.

[eirik]

Thanks for you quick replies.
But what if I instead of using an electric motor use a flywheel. Do you think this can be interpreted as stored energy?
Personally I think this rule can be interpreted in several ways.

[AxelRipper]

That is considered a Hybrid system, which is specifically prohibited.

http://www.flybridsystems.com/

[Racer-X]

I'm not sure how practical a fly wheel is and how much your suspension guys are going to like the idea. As far as the rules go I believe that is ok. Honestly I don't want to read the rules again to check on this. I suggest that you read the rules, write down the explicit dos and don'ts and see if your idea fits.

EDIT: you can't make a hybrid using stored energy, the rules won't allow it. The way it is worded any form of stored energy is prohibited.

[TMichaels]

All of the above answers are correct. A flywheel is also a dedicated energy storage and thus the car would be considered a hybrid. The part starting at "such..." is only an example and does not mean that only using electric motors is prohibited.

[Sormaz]

Tobias,
Where is the line drawn? Sitting at the start of the accel run the typical fsae car will rev its engine up to a couple thousand rpm, storing kinetic energy in the crankshaft, engine flywheel etc...how is this different?

I'd like to replace the differential with an erm.... "inertial device" which is connected to the rear wheels via independent clutches. Run your engine at full load all the time to generate the maximum amount of energy for your limited time on the track (aka you are always producing power, under cornering, braking...) and then drive the car with a right-foot clutch pedal.

I've graduated and as I will not actually be pursuing this design I'm not looking for an official response (which I understand you are unable to give here regardless), but where do you draw the line?

[TMichaels]

To be honest, I do not know where the line is drawn officially(this is always hard to predict as such questions will usually be discussed before an answer is given), but I know what I would add to the discussion:
This rule prohibits any solution, where stored energy can be released in a controlled and delayed manner.

Thus, if you intend to make your crankshaft heavy, fine. You don't have independent control over it. You can only use it to break the tires loose at the acceleration start, but you are unable to use it to boost on the last metres of acceleration.
But if you plan to rev an additional weight up, keep it revving and then later reconnect it, then I would say, this is what the rule is prohibiting.

[eirik]

Thanks for all the replies everyone. Now I understand this rule much better, but still I wont give up the regenerative braking. Let's say I only use the electric motor for braking and not to power the car. And than I use this generated energy for something else. Would this been allowed or is regenerative braking only allowed for EV cars?
I am sorry if this is a stupid question..

[dazz]

Originally posted by Sormaz:
Tobias,
Where is the line drawn? Sitting at the start of the accel run the typical fsae car will rev its engine up to a couple thousand rpm, storing kinetic energy in the crankshaft, engine flywheel etc...how is this different?

I'd like to replace the differential with an erm.... "inertial device" which is connected to the rear wheels via independent clutches. Run your engine at full load all the time to generate the maximum amount of energy for your limited time on the track (aka you are always producing power, under cornering, braking...) and then drive the car with a right-foot clutch pedal.

I've graduated and as I will not actually be pursuing this design I'm not looking for an official response (which I understand you are unable to give here regardless), but where do you draw the line?

I'm pretty sure some modern agricultural tractors have what they term 'hydraulic accumulators' in their transmissions. Not sure how they work though... I imagine some kind of hydraulic coupling that splits some of the torque to the rear wheels when changing up a ratio that pressurizes a hydraulic chamber. This then provides that energy back to the wheels as engine rpms approach the new gear ratio? So kind of like having a rubber band in your drive line for the gear shifts. Of course that could be way off the mark, it's just based on what I feel & hear when driving the things on my family farm (which my folks recently sold...)

[TMichaels]

I see problems in proving in scrutineering that you do not use the motor to propel the car. Additionally, from a design point of view, I don't think that it makes any sense.

[Kevin Hayward]

I the Australian comp last year one of the teams past the finished line of endurance using their starter motor (their engine having died right before the finish line).

Every FSAE car I have seen has both energy storage in the form of a small battery, and a motor that is capable of driving the car (starter motor). What if the battery and starter motor were a little bigger? When do they get big enough that the car is illegal?

How big would they have to get to create some benefit?

Kev

[Crispy]

I think it is pretty clear that the electric starter is not there to power the car. In the cases were the starter has been used to cover the last few meters of an endurance, the team probably should have been disqualified from endurance... but I don't think any of the officials are that heartless.

[TMichaels]

Originally posted by Crispy:
I think it is pretty clear that the electric starter is not there to power the car. In the cases were the starter has been used to cover the last few meters of an endurance, the team probably should have been disqualified from endurance... but I don't think any of the officials are that heartless.

I agree. We also had that once in 2011, I think, where we let a team finish the last 10m with their starter motor.

[Kevin Hayward]

Chris,

I was cheering for the team to finish as much as anyone else. I was just pointing out the fact that the petrol powered FSAE cars are all hybrids with electric motors that run off stored energy. The rules are a little contradictory in the language, although the intent is clear.

If you were prepared to break the rules a few modifications to the starter motor system, a bigger battery and you could certainly build a KERS system that could be hard to detect. Might be one of those things to chuck on the list of cheats you would do if you were prepared to risk the reputation of your team. A list that includes:

- Controlled plenum holes
- Balloons in the fuel tank
- Cut and shut roll hoop tubes with only the right thickness at the inspection hole

and many other stupid ideas.

Kev

[TMichaels]

Kev,
before a team thinks that these cheats are worth the risk, I should add that not only the reputation is at risk, but also the entire future of the team, because I suppose that a team that is caught clearly cheating with things similar to that on your list will be blocked worldwide from all events for at least one season, maybe more.

The last item of your list will at least not work at FSG, as our Scrutineers use ultra-sonic sensors to determine the roll hoop wall thickness at arbitrary points as far as I know.

[AxelRipper]

Actually Tobias, he is quite right, especially regarding rule T3.29 in the FSAE rules. While you need "documentation" that when your hoop was bonded into the monocoque it was the right size, that doesn't mean that the tube bonded into the monocoque is the right size. Unless, of course, the ultra sonic tester can give a full profile of the structure, showing that the carbon is X thick above a tube that is Y thick, it seems that the only place you could feasibly test the thickness of the main hoop is above wherever it is bonded to the monocoque, and the front hoop wherever inspection access happens to be.

[TMichaels]

I agree that, technically, you could get away with for example a front roll hoop completely covered by the lay-up, just being a thin plastic hose. If the scrutineer tries to figure out, if there is steel somewhere by using a magnet, tell him it is stainless. The ultra sonic sensors are not able to pick that up, as far as I know, but I am not sure.

Anyway, I think that you are taking a big risk that is not worth the outcome. Exploiting a grey area of the rules is different to obvious cheating.

[Kevin Hayward]

Tobias,

I 100% agree ... hence the comment about them being stupid ideas. Good to see the use of ultrasonic testers at FSG. A regulation that can't be checked for compliance is useless.

I also couldn't imagine what it would feel like to do well in Formula while cheating. I have never understood why it happens so much in some fields of professional racing. It just seems a way to make big achievements feel hollow.

Didn't mean to sidetrack the topic though. The simple fact is that we have hundreds of cars produced each year that use an electric motor powered by stored energy to start the car, and a few cases where cars have been propelled by those motors. I would suggest that there could be a couple of words added to the rules outlining the purpose of the battery on the car for an IC vehicle, maybe even stating a maximum voltage/capacity. Now that we have the Electric rules in the rulebook it would be quite easy to borrow some of the wording to put a cap on this for IC cars.

Kev

[Kevin Hayward]

Tobias,

Some of the cheating ideas are what I would call beer ideas. Many times when having a beer with team-mates (or now students) we have come up with many ways to confuse the scrutineers to make the unbeatable FSAE car.

As more beer gets consumed the ideas get more ridiculous, and the scrutineers get more gullible.

Kev

[TMichaels]

I have never understood why it happens so much in some fields of professional racing. It just seems a way to make big achievements feel hollow.
Maybe, because professional racing has become mainly economics and is not about passion anymore.


Didn't mean to sidetrack the topic though. The simple fact is that we have hundreds of cars produced each year that use an electric motor powered by stored energy to start the car, and a few cases where cars have been propelled by those motors. I would suggest that there could be a couple of words added to the rules outlining the purpose of the battery on the car for an IC vehicle, maybe even stating a maximum voltage/capacity. Now that we have the Electric rules in the rulebook it would be quite easy to borrow some of the wording to put a cap on this for IC cars.

The rules could limit the power of the starter motor for example, but that would be hard to check. Given that usually teams are arguing that the rules should become simpler, somethings like this add unnecessary wording in my opinion.

But the other point you made struck me, as being a sparkie, like a lightning: There is no limit on the maximum voltage being used in an IC car...although I am pretty sure that 800V IC cars will be rejected at scrutineering (but currently only based on rule A3.10) and would not really make sense, it is still not prohibited by the rules.

[AxelRipper]

Originally posted by TMichaels:
But the other point you made struck me, as being a sparkie, like a lightning: There is no limit on the maximum voltage being used in an IC car...although I am pretty sure that 800V IC cars will be rejected at scrutineering (but currently only based on rule A3.10) and would not really make sense, it is still not prohibited by the rules.

Finally! A solution for a hard to start single! Screw 24v start, give me 800!

Beer ideas are definitely good. Would almost be enough to either keep dragging this thread off topic, or just make a new one.

You know, a carbureted engine generally has to have a tank to gravity feed the carb to work properly. If you fill the carb bowl and this tank before endurance fueling, then drain it back afterwards......

[Z]

If I may get back on topic, this is another example of a badly written FSAE Rule.

Along with Kevin's example of the battery and starter motor, I remember discussion from years ago about stored energy in pneumatic accumulators (common in gearshift systems). And, of course, there is the engine flywheel (see below).

The relevant section should either be rewritten more precisely, or, better yet, get rid of it and allow "creative and imaginative" fuel efficient cars.
~~~o0o~~~
eirik,

You might consider an alternator (= battery charger) connected to the final drive, but only operating when the brake light is on or the throttle is at less than 50%. This would give some "regenerative" braking (storing energy in battery for later use by electrical system), while allowing more WOT power. Not as effective as a full regen system though...
~~~o0o~~~


Originally posted by TMichaels:
A flywheel is also a dedicated energy storage and thus the car would be considered a hybrid [and prohibited]

Originally posted by Sormaz:
Where is the line drawn?
...
I'd like to replace the differential with an erm.... "inertial device" which is connected to the rear wheels via independent clutches. Run your engine at full load all the time to generate the maximum amount of energy for your limited time on the track (aka you are always producing power, under cornering, braking...) and then drive the car with a right-foot clutch pedal.
Or, perhaps fit your car with a small engine (~100cc, constantly running at WOT for best fuel efficiency) that has a high MoI flywheel. Then drive the rear wheels through an IVT or CVT.

As the car accelerates down the straight the engine RPM reduces as energy is taken from the flywheel and converted to car KE (equivalent to shifting-up through the gears). At the braking zone the engine RPM increases, due to "engine braking" storing car KE in the flywheel (equivalent to using the gearbox to slow the car, and quite legal). Through the corner the engine RPM keeps increasing as fuel energy is stored in the flywheel (also legal). Repeat for next straight...


Originally posted by TMichaels:
To be honest, I do not know where the line is drawn officially ...
but I know what I would add to the discussion:
This rule prohibits any solution, where stored energy can be released in a controlled and delayed manner.

Thus, if you intend to make your crankshaft heavy, fine. You don't have independent control over it...
Tobias

As noted in my above example, all current cars DO have independent control of the energy in their engine flywheels. This control is either through the throttle, or the transmission, and can be "released in a controlled and delayed manner".

So the big question. Would you ban such a car (ie. heavy flywheeled 100cc single with I/CVT)?

Or would you support such a ban if it was initiated by another official, perhaps one with a prejudice against the team?

And, BTW, what are your views on the "creativity and imagination" section of the rules? Should it be deleted?

Z

[Bemo]

To come back to the rule prohibiting hybrids. I also remember when a team from Berlin finished Endurance using the starter for the last meters of Endurance.
My opinion is that if you interpret the rule strictly, you would have to disqualify that team as it is not allowed to propel the car by using stored electric energy but as others already stated that would be a heartless decision as it is pretty clear the team never planned to do so and their time is ruined anyway.
In theory I'd say there is no rule prohibiting to store electric energy from braking and then using it only for ECU etc. instead of the regular generator. BUT there remain questions:
1) How do you want to prove the motor is really only for braking? Scrutineers will be very critical about that.
2) Is it really worth the effort if you don't propel the car with the stored energy? I know that some new passenger cars control the generator in a way that it is only active while braking to increase the overall efficiency of the car. I'm not quite sure if this makes sense in a FSAE car as the electric energy consumption is much lower compared to a modern passenger car.

If you want to do stuff like that, I'd say you have to build an electric car. In FSE regenerative braking obviously makes a lot of sense if the system is working properly.

[Big Bird]

My question to the original poster is:

How much of the energy expended in propelling such vehicle around the track, is available for regeneration?

How did you estimate that?

[Kevin Hayward]

How about this:

Small engine
CVT
No alternator
Electric motor to drive a decent supercharger
Enough battery power to last the endurance event before being drained.

Should be able to do that with little to no weight gain (maybe even a loss) and get a big fuel economy advantage.

Kev

[Bemo]

@Kev: Why a CVT (I guess for running the engine in its ideal load points). Usually this type of transmission is pretty inefficient. I'm pretty sure you would be more efficient with a regular three or four speed transmission should be more efficient and much simpler.
But the idea to use a small engine with an electric supercharger is really nice. But if you want to drive without an alternator you definitly have to regenerate braking energy, otherwise the battery will get way too big. I'd say the rules allow to use regenerated braking energy for running a supercharger as it doesn't propel the car directly.

[Jan_Dressler]

The engine(s) used to power the car must be a piston engine(s) using a four-stroke primary heat cycle with a displacement not exceeding 610 cc per cycle. Hybrid powertrains, such as those using electric motors running off stored energy, are prohibited. Note: All waste/rejected heat from the primary heat cycle may be used. The method of conversion is not limited to the four-stroke cycle.

Originally posted by TMichaels:
I see problems in proving in scrutineering that you do not use the motor to propel the car. Additionally, from a design point of view, I don't think that it makes any sense.
So what about the sentences in bold?

Let's say you use a method to convert "waste/rejected heat from the primary heat cycle" to electricity... In my understanding of the rules, you would be allowed to use this to directly power an additional electric motor.
Or to charge your batteries when additional power is not needed, such as under braking (maybe additional to some kind of regenerative braking). So you have "wiring" between your battery, "waste heat recovery device", some kind of controller, and your motor/generator.

I think it would be VERY difficult to prove to the scrutineers that you don't use "battery power" instead of, or additionally to "waste heat recovery device power" to power your motor - although the system would be perfectly legal if you don't.

Jan

[eirik]

I have just read the 2013 rules for FS and see what I found http://fsae.com/groupee_common/emoticons/icon_cool.gif

IC5.4.4: Hybrid powertrains utilizing on-board energy storage are allowed.
Why is this legal in FS but not in FSAE?
Bemo and Big Bird:
If it really is worth the effort to put a regenerating system in the car I must say I don't really know yet. In fact, as I was hoping that someone with a bit more experience than me could have helped with that. But what I know is that it is innovative, and if it works properly, good engineering work.
z:
Sorry for my ignorance but what do you mean by WOT?

[Z]

Originally posted by eirik:
... what do you mean by WOT?
eirik,

"WOT" = "Wide Open Throttle".

So NO alternator drag when you have right foot flat to the floor, and want maximum power for maximum acceleration.

Z

[DougMilliken]

Originally posted by TMichaels:
Maybe, because professional racing has become mainly economics and is not about passion anymore.

Going waaaay off topic here--I couldn't resist passing along EJ Potter's words of wisdom, "... During my so-called career, I saw the corruption of boat racing, stock car racing, drag racing, and tractor pulling. All these initially noble institutions were degraded into a state of prostitution and sleazy phoniness by the corrosive effects of sponsor money. Ironically, most participants of all these motor sports were all knees and elbows rushing pell-mell down the road to hell in a handbasket by their lust for the dollar, the very instrument of evil that would inevitably seal the doom of the sport they all loved to the point of fanaticism. ..." From:
http://www.draglist.com/artman...s/article_1030.shtml (http://www.draglist.com/artman/publish/daily_stories/article_1030.shtml)
He proposes a solution to get back to the "thrill of the motor", in part two:
http://www.draglist.com/artman...s/article_1031.shtml (http://www.draglist.com/artman/publish/daily_stories/article_1031.shtml)

EJ Potter died earlier this year, there are many obits on the web, I liked this one:
http://thekneeslider.com/archi...chigan-madman-r-i-p/ (http://thekneeslider.com/archives/2012/05/03/e-j-potter-the-michigan-madman-r-i-p/)

[Bemo]

Originally posted by eirik:
I have just read the 2013 rules for FS and see what I found http://fsae.com/groupee_common/emoticons/icon_cool.gif
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> IC5.4.4: Hybrid powertrains utilizing on-board energy storage are allowed.
Why is this legal in FS but not in FSAE?
Bemo and Big Bird:
If it really is worth the effort to put a regenerating system in the car I must say I don't really know yet. In fact, as I was hoping that someone with a bit more experience than me could have helped with that. But what I know is that it is innovative, and if it works properly, good engineering work.
z:
Sorry for my ignorance but what do you mean by WOT? </div></BLOCKQUOTE>
Well, the organisers of the UK event are going a different way than most other comps. They want to have various powertrains competing next to each other within one class. Formula Germany for example has quite a different philosophy (which makes more sense in my opinion). They have two seperate classes for IC cars and electric cars. Like this it is much easier for the scrutineers to check the cars for safety because every concept brings different kinds of hazards and by limiting the allowed concepts it is easier to prepare.
The other problem with having different kinds of powertrains competing in one class is that you will always have an endless discussion which concept is favoured by the rules. Scoring for energy efficiency is only one example...

While you're new in FSAE you shouldn't try to be the most innovative team ever. That's not the task and if you ask me it is also wrong to think that you have to realize the most special concept to do good engineering. Choosing a simple concept but really understanding how it has to be done can be much better engineering. Remember the task is to score as many points in the dynamic events as possible. Good engineering is to achieve that with least possible effort http://fsae.com/groupee_common/emoticons/icon_wink.gif

[Big Bird]

Originally posted by eirik:
I have just read the 2013 rules for FS and see what I found http://fsae.com/groupee_common/emoticons/icon_cool.gif
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> IC5.4.4: Hybrid powertrains utilizing on-board energy storage are allowed.
Why is this legal in FS but not in FSAE?
Bemo and Big Bird:
If it really is worth the effort to put a regenerating system in the car I must say I don't really know yet. In fact, as I was hoping that someone with a bit more experience than me could have helped with that. But what I know is that it is innovative, and if it works properly, good engineering work.
z:
Sorry for my ignorance but what do you mean by WOT? </div></BLOCKQUOTE>

You probably should think about it the following way:
Aerodynamic drag is a loss you can't recover.
Rolling resistance is a loss you can't recover.
Kinetic energy us something you can recover
You need either a log of vehicle speeds around a typical track, or, if you are feeling game, a track map so you can write your own lapsim. Your lapsim doesn't need to be too highly detailed or accurate.
You will need to break your track into, say, 1 metre increments, and estimate or calculate a velocity for each increment.
Calculate or estimate for each increment:
Aero drag force (00.5*rho*frontalarea*Cd*V^2)
Aero drag energy (=drag force * increment length)
Rolling resistance force (for an estimate attach a spring balance to your roll hoop and drag the car around at constant speed - record average force). If your car isn't done - offer to do someone elses.
Rolling resistance energy (= force* increment length
Sum all the energy losses for each increment around the track, find total irrecoverable loss.
For each straight, calculate kinetic energy change between fastest point and the slowest point on the straight - this is your recoverable energy loss.
Sum up all your recoverables, find out the ratio
[recoverable / (recoverable+irrecoverable)]
Depending on the track I'd estimate around 20-25% recoverable (ideal case)
Then you might want to estimate the proportion you might realistically regenerate (using the efficiency of the regeneration system)
You might be down around 10% now
You might like to then recalculate your velocities and recoverable energy change using your new vehicle mass and power output (with hybrid energy system in place).
You can compare the different track lap-times for the standard to hybrid vehicle to estimate how many extra points you could score.

If it all sounds too hard, start with a really simple constant acceleration lapsim around a really simple track of your own design with maybe 2-3 straights and 4-6 turns.

You will learn lots about where you get good points returns, and where you don't, by going through this exercise.

Cheers

[TMichaels]

You might be down around 10% now
Based on my experiences from the past events, where I evaluated the EnergyMeterData aka energy flows of the electric cars, this number is an underestimation.

I can't be more specific, since we agreed with the teams that the recorded EnergyMeterData is confidential until they release them.

[eirik]

Thank you so much for very good and informative answers everyone, and especially to Big Bird for your help. I have only read quickly through you last post but it looks like a very good way to do it. And Bemo you have a really good point, thanks for the reminder http://fsae.com/groupee_common/emoticons/icon_smile.gif

Good engineering is to achieve that with least possible effort http://fsae.com/groupee_common/emoticons/icon_wink.gif
Now I will try to calculate how much energy it is possible to regenerate, and find out if it really is worth the work. But I am afraid that this will take some time, especially to get good data. Hopefully it will be worth the time spent.

[Big Bird]

No problems Eirik, it is nice to get some interesting questions and discussion going on here.

And whether or not you decide to go ahead with a regenerative system, time spent learning why or why not it is suitable will always be time well spent.

Good luck, let us know how you go.

Cheers,

Geoff

[Z]

WHY REGENERATIVE BRAKING?
===========================

Just some miscellaneous rambling on this subject... (yawn... http://fsae.com/groupee_common/emoticons/icon_smile.gif ).
~~~o0o~~~

Going fast around a racing circuit can be done in two main ways.

1. Maximise Longitudinal Gs.

This is the traditional approach. Here a big powerful engine is fitted to a small car, allowing tyre-smoking, neck-snapping acceleration at the beginning of each straight (positive-longitudinal-G). Similarly, at the end of the straight, brutal braking is required so the car can tip-toe around the next corner (negative-longitudinal-G). Repeat for next straight...

2. Maximise Lateral Gs.

Here the car is fitted with an embarrassingly small engine, possibly because of cost restraints. So the designers concentrate on improving corner speeds by increasing lateral Gs. Now the car maintains a rather boring, almost constant speed around the track, albeit with laptimes that are often less than the #1 cars above.
~~~o0o~~~

Consideration of the Mechanics of the two approaches shows that #1 is extremely energy INEFFICIENT, while #2 is much more efficient. Briefly, energy, a scalar quantity, is the "scalar product" of force and distance vectors. When these two vectors are parallel, as with longitudinal Gs, the energy production or destruction is at its maximum. When the two vectors are perpendicular, as with lateral Gs, the energy change is zero. So, energetically speaking, lateral Gs are free!

The inescapable fact is that conventional #1 cars burn a lot more fuel than #2 cars, as well as being more expensive to build in the first place (bigger engine and brakes). So occasionally #2 cars are allowed to enter, and indeed win, race series. Witness the Mini "brick" versus the might of the Holden and Ford V8s in the 1960s Australian Bathurst races. But for reasons probably related to testosterone, most people involved in racing, mostly young men, believe that "real racecars" are like #1 above, and the #2 approach is for pussies. So, the rules are rewritten, and the boring #2 cars are squeezed out.

But what about fuel efficiency, and "greenliness"? Well, with the recent rises in fuel prices, and for other eco-nonsensical reasons, the notion of having #1 cars that are also fuel efficient has arisen. This can be achieved by capturing ("regenerating") the normally wasted brake energy, and then using it for the next acceleration run. The "hybrid racing car" is born. However, despite green supposedly being good, this concept is still meeting considerable resistance in racing series from F1 down to FSAE.
~~~o0o~~~

Now for the slightly bizarre part. Though most FSAE students are not allowed to design hybrid ("regen") cars for FSAE, they will probably have to do so if they end up in the mainstream auto industry. This will be mainly for marketing reasons (!), but it makes a mockery of claims that FSAE is about "education rather than racing".

And here is the even more bizzare part. For the majority of mainstream production cars, regenerative braking is a wank! It is really not worth it. Not only is there the cost of the extra equipment, and the conversion losses to and from the energy store, but for most cars, most of the time, it would not be used.

IMO the only vehicles that can significantly benefit from regen are circuit racing cars, and inner-city buses. Cicuit racing cars because they have to go fast around circuits specifically designed to repeatedly slow them down with corners and chicanes. And inner-city buses because the woosy urbanites don't like jumping on or off fast moving vehicles. Google various flywheel and pneumatic energy storage bus prototypes built in the 1970-80s to see that this problem was identified, and addressed, a long time ago.

A better approach to "fast and fuel efficient" for racing cars is efficient aero downforce that allows faster cornering. Of course, racing being racing, the rules invariably evolve to mandate the loudest, most expensive, and least efficient solution possible. Witness the DeltaWing, proposed as a better IndyCar, but ultimately rejected and replaced by the grossly inefficient same-old same-old.

For production cars the solution is better roads with fewer sharp corners, and no traffic lights! But that also requires better governments, so Buckley's chance there! So the answer, again, is simply to go fast around corners. Along with the Mini brick (many times Monte Carlo Rally winner), another good example is the Citroen 2CV, which was developed for the poor road conditions of pre-WWII France.

The four-door, four-seater, quite spacious 2CV was originally fitted with a 375cc air-cooled flat-twin. In "big-block" form this grew to 602cc, so still quite economical. Driving technique is start with right foot flat to the floor (for maximum engine efficiency), row the car up to speed with the gearbox, then never "lift" until you reach your destination. Certainly, never, ever, touch the brakes! This is made possible on all sorts of roads and corners by the exceptionally good ride and grip of the interconnected leading and trailing-arm suspension.
~~~o0o~~~

FSAE is held on smooth tracks, so the cars don't need advanced 2CV-like suspension. However, efficient aero, and a similar overall philosophy and driving style to the 2CV, seems like a good recipe... http://fsae.com/groupee_common/emoticons/icon_smile.gif

Z

[Kevin Hayward]

Z,

This time I find it difficult to see where your usual anger/disappointment is targeted.

#2 cars are welcome in FSAE, if anything they are mandated. The guys at ECU take there car up to local hillclimbs for some testing. When it has run it has soundly beaten a lot of heavily modified and powerful road cars, as well as purpose built supercharged hyabusa powered single seaters. Often using tyres that some FSAE cars use. When it hasn't won it has come 2nd or 3rd.

Whenever it has been up there I have never heard any of the opposition make the claim that the 20mm restricted 600cc engine was a big engine.

The 600s may be the big blocks of FSAE, but it is hardly a fair comment to say that the students would always want bigger. An unrestriced 5000cc v8 might produce more power, but I think that just about every team would decide it would not be the ideal engine to put in a car for a FSAE event.

On the other hand no one would suggest that a 5cc engine would be the ideal engine size for FSAE. So somewhere between 5 and 5000cc there would likely be an ultimate engine size and power for FSAE. We seem to lower this to about 250cc to 600cc, with weight of the package being critical. We would always take maximum torque/power if weight between packages was equivalent.

...

That gets to the fundamental issue of regen in FSAE ... is it worth the weight? For other forms of motorsport where the batteries look a lot like ballast this is not an issue and as Z has mentioned will help a circuit car.

Without doing the simulations I would think that the brown go-kart would use less fuel than the more complicated regen based car and probably be faster. Given the legality etc. I wouldn't bother doing this particular simulation. While the result would be interesting it would almost certainly be a waste of time, and anyone who has been involved with sizeable projects know is that time is critical. Perfect is the enemy of finished.

In this case I would be making an initial decision based on resource allocation. Regenerative systems take a long time to develop and integrate well. In order to invest this the gain you need to make needs to be of the order of magnitude of other things you could be doing with your time. In this case that is highly unlikely.

One of our common failings as engineers is that without care we devolve into scientists or specialists. We are supposed to be problem solvers. Each person entering a team should be thinking:

"What can I do that will provide the greatest benefit to the team"

This can involve some very unappealling answers. You may be best placed to do sponsorship drives, or sweeping the floor, or writing the cost report, or practicing machining. Even as a designer it might mean giving up on the turbo shifter system with artificial intelligence for a simple steel rod. Instead we tend to come in thinking:

"What do I want to do"

This is dangerous because not just because it can lead to non-competitive teams, but more so because we end up training ourselves as geeks of the world instead of its problem solvers.


eirik,

Unfortunately as an engineer you will have many times in your career where you will need to assess the expected outcomes of your work well before you do the work. You are going headlong into a lengthy process of simulation and concept design before doing some simple approximations. Your time is very valuable, and you should have a rough idea of whether that is the best use of your time or not. Don't make the mistake of asking youself the question of whether regen is better or not. Try to come at this problem from earlier on in the design phase. Identify all of the things that may benefit the car and team. In a small amount of time as a team you will be able to rank these ideas reasonably accurately. Then attack the low hanging fruit.

Leave the fruit perched at the top of the tree for those that want to fall off their expensive supercharged bluetooth carbon composite ladders.

Kev

[HD]

Originally posted by Bemo:
While you're new in FSAE you shouldn't try to be the most innovative team ever. That's not the task and if you ask me it is also wrong to think that you have to realize the most special concept to do good engineering. Choosing a simple concept but really understanding how it has to be done can be much better engineering. Remember the task is to score as many points in the dynamic events as possible. Good engineering is to achieve that with least possible effort http://fsae.com/groupee_common/emoticons/icon_wink.gif

While i agree with you to some extent there are probabliy several ways to interpret the meaning of the phrase 'Good engineering'.

Obviously, a first year team probabliy shouldn't spend all their time focusing on innovation; there are several examples in FSAE/FS of how that has gone terribliy wrong. Having said that, every team has its own profile and strategy.

In my opinion, you should never let the obsession of scoring well in the dynamic events prevent you from choosing a different and interesting approach during the design phase of your project(obvious limitations apply here). Its much more important to have a good time along the way, than acheiving the last 5% score in the competition.

[Big Bird]

I actually agree with Z here. An autocross or endurance event is won by the team with the highest average velocity. We assume that to get highest average velocity, we need the highest acceleration. But if we can achieve a high average velocity with minimal change in velocity, we actually put ourselves at an advantage. Remember it is acceleration, not velocity, that creates forces in a system.

This was actually the philosophy behind the first RMIT single cylinder cars. We were trying to build a car that was almost as fast in the corners as it was in the straights. Low power means low straight-line speed, low weight equals high cornering speed, narrow track means a more sweeping pass through the corners. This lesser change in speed would mean less fuel usage, and my own personal opinion was that the lessor the change in velocity on corner entry, the more likely the driver would hit his turn-in points and follow the right path.

That was the thought behind it all anyway.

Cheers all

[RicardoF]

Hello Guys,

Let me take advantage from this topic to ask you something.

We are currently designing our second electric car and it is the first one where we are working on regenerative braking.
We only have motors in the rear axle.
We want, at a given travel of the brake pedal, to use the front hydraulic circuit for braking the front wheels and our motors to brake the rear wheels while regenerating.
This means that we cannot actuate the rear hydraulic circuit at this specific moment.
We arranged a mechanical configuration in order to use only one master cylinder up to a specific position of the pedal and only then, the two master cylinders.
This is a tricky solution so we are considering other options. Do you know about any valve that we can put on the rear circuit in order to achieve this goal?
What strategy does your team use?

Thank you,

Ricardo Ferreira
Technical Director
Projecto FST Novabase

TU Lisbon - Instituto Superior Técnico

[Racer-X]

I can't think of a valve that would work both ways, and prevent the brakes from locking up. Why not use the mechanical linkage? The only issue I see with that is maintaining brake bias.

[Z]

Originally posted by Kevin Hayward:
Z, This time I find it difficult to see where your usual anger/disappointment is targeted.
Kevin,

It was mostly "miscellaneous rambling". http://fsae.com/groupee_common/emoticons/icon_smile.gif

In an earlier post I described an efficient #1 car (100cc-single+flywheel+IVT), but I wanted to make it clear that I think the #2 approach is better. Was also ranting at mainstream motorsport (mainly "Formula") that seems to love inefficiency, as with the rejection of the DeltaWing. Oh, and also at the fact that many production cars will soon be sold with "Regen-capability" ("It's our never ending quest for greater efficiency..."), even though it's a wank.
~~~o0o~~~

Geoff (& others interested in #2 cars),

I remember riding in the archetypal #2 car about 50 years ago. It was "The Mighty Mouse" at Sydney's Luna Park. This was a mini roller-coaster, but without all the hills and dales. The usual chain-drive dragged the cars up to the top of the structure, but from there it was a fairly constant, gentle down-hill slope all the way to the end (just enough slope to overcome wheel and air drag at a given speed). So very little longitudinal Gs, but instead a never ending precession of left and right hairpins, guaranteed to leave you black and blue in places you didn't know you had! Fun!!! http://fsae.com/groupee_common/emoticons/icon_biggrin.gif.

I believe a similar ride is still there. Anyone considering "big picture" FSAE concepts should buy a ticket...

(Incidentally, I don't think the current ride is the original one. The one I remember was a masterpiece of old-school engineering. It was made entirely of 1"x1" MS angle irons, held together mostly by paint, and the occasional, rusty, hardware store bolt. I think all the stick-slip looseness of the bolts was to suppress resonant vibrations in the structure. Internal damping, you know...)
~~~o0o~~~

Last bit of waffle...

Spec formula racing is well known to be incredibly boring. The cars have very equal performance, so very little overtaking. But I have a solution!

I have actually thought this through in a lot of detail, but briefly... The solution is the "Dual-Spec Formula". Here half the grid are #1 cars, 500hp dragsters with big, fat, rear tyres, but no aero downforce. The other half are #2 cars, with pissweak 200hp engines, smallish equal sized tyres, but very efficient low-drag, high-downforce aero. The organizers have adjusted performance so that both types of car have very similar overall lap times.

On every straight the dragsters blow the pussy aero-cars into the weeds, with half the field passing the other half. But at the end of the straight the dragsters have to slam on their brakes, and the aero-cars tootle past them around the corner. I reckon the most exiting part of it all would be waiting for the exact moment when the race commentator's hernia pops, as he tries to call all the passing manoeuvres! (Picture Martin Brundle calling a single F1 pass, then multiply by Half-field x Number-of-corners x Number-of-laps. http://fsae.com/groupee_common/emoticons/icon_smile.gif )

Z

[murpia]

Originally posted by Z:
On every straight the dragsters blow the pussy aero-cars into the weeds, with half the field passing the other half. But at the end of the straight the dragsters have to slam on their brakes, and the aero-cars tootle past them around the corner. I reckon the most exiting part of it all would be waiting for the exact moment when the race commentator's hernia pops, as he tries to call all the passing manoeuvres! (Picture Martin Brundle calling a single F1 pass, then multiply by Half-field x Number-of-corners x Number-of-laps. http://fsae.com/groupee_common/emoticons/icon_smile.gif )

Z
What you describe already kind if exists in historic touring cars: Mini Coopers vs. Ford Galaxies, for example.

Google 'Mini Cooper S Racing Against Huge 7ltr Ford Galaxie 500. Goodwood Revival'

Regards, Ian

[rjwoods77]

Originally posted by murpia:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:
On every straight the dragsters blow the pussy aero-cars into the weeds, with half the field passing the other half. But at the end of the straight the dragsters have to slam on their brakes, and the aero-cars tootle past them around the corner. I reckon the most exiting part of it all would be waiting for the exact moment when the race commentator's hernia pops, as he tries to call all the passing manoeuvres! (Picture Martin Brundle calling a single F1 pass, then multiply by Half-field x Number-of-corners x Number-of-laps. http://fsae.com/groupee_common/emoticons/icon_smile.gif )

Z
What you describe already kind if exists in historic touring cars: Mini Coopers vs. Ford Galaxies, for example.

Google 'Mini Cooper S Racing Against Huge 7ltr Ford Galaxie 500. Goodwood Revival'

Regards, Ian </div></BLOCKQUOTE>

I remember watching an old black and white movie on an old touring race on Speedvision many years ago. The Galaxie was going head to head with a Lotus Cortina and destroying everything but had to stop every 7 laps or so to replace its brake pads.

[Bemo]

Originally posted by RicardoF:
Hello Guys,

Let me take advantage from this topic to ask you something.

We are currently designing our second electric car and it is the first one where we are working on regenerative braking.
We only have motors in the rear axle.
We want, at a given travel of the brake pedal, to use the front hydraulic circuit for braking the front wheels and our motors to brake the rear wheels while regenerating.

I guess the idea behind that approach is that you can get more regenerated energy out of it. But you should be very careful about your brake bias. The driver shouldn't feel a difference in the pedal when he reaches the point, at which the hydraulic system is actuated. I would rather suggest to use the hydraulic system from the beginning and letting the motors brake with a proportional force. Like this it will be much easier to realise a working system which doesn't change the feedback the pedal gives to the driver. Of course you will regenerate a little less energy, but you don't have to lose much time on the track due to weird braking behaviour to ruin all your gains from efficiency in your overall scoring.

In the end the potential for regenerative braking is quite low if you have only motors in the rear. Some guy from our team made a simulation for that for our first car (I don't remember the exact numbers, but it was quite low) and then we decided that it's not worth it.

Just my opinion. You may try to proove me wrong - that's what FSAE is about ;-)