Input on ESC systems...

[Dave K]

I am pondering some research on running an electronic stability control system on our car next year. If any of you have experience with this, i was wondering if i could get some input on the pros and cons... cost, required experience/difficulty level, time, etc. I have the basic concepts on the control logic behind it all, but other than that i am pretty new to it. Any replies will help.... thanks.

[screwdriver]

Not an easy task, if you build the control-system yourself. If you can find an off the shelf solution, it'll be quite simple (and you probably won't learn much).

I would be concerned, if they are allowed at all, since the rules are quite explicit about the brake system afik.
The other thing you'll have to think about is, if that will make you go any faster. Imho all that TC and ESC systems are the wrong way to go when it comes to speeding things up, since they tend to slow you down rater than make you faster. That is, if you have experienced drivers, of course.

[Pete M]

If TC makes you slower then why do Formula One teams always use it whenever it is legal?

The TC and ESC systems in production cars tend to be overly aggressive to stop people who can't drive from getting in trouble. A racing setup would be configured differently.

I don't think stability control would be necessarily illegal either. So long as it can only ever add to braking force rather than subtracting, then it isn't really a safety issue. Check with the rules committee though.

[Dave K]

If i'm not mistaken, i think you can use an engine cutout to either assist or replace braking (at least with TCS).

[exFSAE]

How exactly would you do this? Along with what Josef is saying..

TCS is typically done by a combination of modulating fuel, spark, throttle, and clutch. Fuel/spark are easy fast controllers. Throttle isn't allowed. Clutch is difficult. It is hard enough to get a good traction control system working. Start with that as a lofty goal.

Vehicle stability control is typically done by individually braking wheels to reel in excessive US/OS. Not allowed. Brakes have to be manual.

It'd have to be QUITE the impressive control system too. Taking into account true accelerations and yaw rates, tire traction limits as loads change, plus all sorts of nonlinearities in the car. Throw that PID stuff out. But I assume you have a background in nonlinear controls and know this..

[PatClarke]

Not allowed. Brakes have to be manual.
Not necessarily so. I am sure that an application to the Rules Committee would be judged favourably as long as the primary 4 wheel braking system is a manual system and cannot be affected in any way by the ESC.

Quote "If TC makes you slower then why do Formula One teams always use it whenever it is legal"?
Pete, F1 cars are deliberately traction limited, FSAE cars are not.

My 2 cents worth...Anything that puts the brakes on on an FSAE car is not what you want to go fast.

If your thoughts are that the Judges will be impressed, well, maybe, but probably not.

Cheers
Pat

[TMichaels]

We used an ABS-System last year and I have to say, it really makes us faster, since the pressure gradient applied by the driver can be at maximum without running into blocked tires. Therefore you win meters when beginning to brake. The other thing is, that you can brake right into the corner, because the ability to steer still persists.

Regarding the rules committee: we had to prove that it is fail safe and that we always have the ability to brake.

Regarding the TCS-Formula1-Thing: FS cars are not always power limited and just to add it: Formula 1 also used ABS while it was allowed. All these electronic gizmos make you go faster, if they are done properly. Please don't compare the race setup of such a system to a production car. We all know, that these setups are for safety reasons and not to let Aunt Emma pass the next turns with maximum speed in her Fiat Punto while driving to the supermarket to get new milk.

BTW: The Chief Design Judge of the FSG drove our car and liked the ABS very much: http://fsae.com/eve/forums/a/tpc/f/825607348/m/93210861...10332341#78210332341 (http://fsae.com/eve/forums/a/tpc/f/825607348/m/93210861341?r=78210332341#78210332341)

In short: If you do it well, it makes you faster otherwise it will only be added weight, complexity and cost.

Regards,

Tobi

[PatClarke]

Hi Tobi,
We weren't talking about ABS!
I watched your ABS car perform and I was impressed.
Pat

[Fil]

Doing ESP on an FSAE car would be a very large undertaking. ABS can be done fairly simply on an FSAE car because there is a Bosch motor sport ABS system on offer or you can do what braunschweig did and get conti to support you. An ABS system also is far simpler in developing since its primarily used to prevent lockups and allow steering while threshold braking, which means there are far less parameters to take into account, far less complexity(relative) and less chance of making the car uncontrollable. Its not actually used to reduce stopping distance, although you are able to tune it to suit your needs.

I work for Bosch as part of the ESP application department and i know what goes into a full ESP/ABS/TCS system (its not easy task). We use full theoretical models approximating everything from normal loads, to individual tire friction coefficients and individual wheel slip angles. there is a whole heap of information required to make an esp system work properly. The hydraulic unit used for ESP have greater control of the individual brakes but it is bigger and heavier and much more expensive than the equivalent ABS system. There is a lot of specialized equipment that needs to be used and calibrated for the system to function properly too. Sensors alone you need steering angle, individual brake pressures, lateral g's, yaw rate, slip angle, wheel speeds and sometimes even brake temp depending on how hardcore you want to go with it. It just depends on what your performance targets are for the system. I was looking at putting an esp system on our car that can help with individual wheel braking for slaloms, but looking at it its a serious undertaking for one person and our team doesn't have the resources or the time to do something as fancy as that(a simple car is difficult enough for one year).

At bosch we have team of about 25 guys(mostly ex-FSAE) working on specific ESP application projects not including the guys who write the actual base software for the system. There are hundreds of people who are dedicated to writing the ESP software. That said, a lot of the code is also for situations that we would never see, but at the same time the logic that goes into figuring out all of the different calculated parameter (in the Bosch system there are something like 60,000 parameters that can be changed and a similar number that are calculated) these all make the system robust and adaptable to different situations. You could write a simple bit of code, but to get it to work properly would take some serious time, resources and effort, which in FSAE you don't have a lot to devote to something that might not necessarily work how you would expect it to.

The ESP units are able to build pressure on their own and can actually build pressure without driver input, im wondering if that falls within the rules? The whole idea behind it was that you can control each individual wheel so the right amount of pressure can be distributed and removed at the computers discretion. On some cars if you stab the brake and the computer thinks you should be braking harder it will actually brake on its own accord. would that be considered a loose version of brake by wire?

i hope this sort of helps

[Mike Hart]

Pat. Not sure who it was I spoke to at Lions about it, but their ABS module did actually have the capacity to do some form of ESC apparently....only they didn't use it!

Personally, I think you could use it quite effectively, but you'd have to approach it in a completely different manner to a 'Stability Control' system. If you could somehow implement it in a similar way to the McLaren third brake pedal (ie braking the inside rear when accelerating) then it could potentially be very effective on something like skidpan or in some aspects of the autocross. Doing this though would be very difficult and furthermore, getting the correct amount of brake pressure to get the desired amount of torque transfer across the diff could be a little bit interesting.

Another thing to think about with these systems is brake temperatures. Remember that our ave speeds are very low and hence, if you're brakes are constantly on, it won't be long before their cooked. Your diff and drivetrain would also have to be beefed up too since you would be putting repeated reverse torque loadings through your drivetrain.

[Dave K]

I'll have to check with the rules commitee on the brake-by-wire concern.. i could see how that would affect the decision.

I don't doubt this is a huge undertaking, but i would assume that since it would be tuned to only assist with high oversteer and understeer, it could only help and make you potentially faster. I mean, on production cars it is meant for our Aunt Emma going to the grocery store, but for racecars it would be meant for any time we might slip in concentration and put too much throttle in a corner or the like...

however, i could also see how ABS would be beneficial in this same area as well, allowing later braking into a corner and therefore maximum traction.

I noticed also that the equipment for ESC would be fairly expensive, yaw sensors alone seem to be ranging in the $600+ range (from the little bit of google searching i have done so far).

[Pete M]

Pat, i'm not sure where you got the idea that FSAE cars weren't traction limited. I think a decent fraction of the field would be faster with a well tuned TC system than without.

[HenningO]

Originally posted by Dave K:
I don't doubt this is a huge undertaking, but i would assume that since it would be tuned to only assist with high oversteer and understeer, it could only help and make you potentially faster.

I noticed also that the equipment for ESC would be fairly expensive, yaw sensors alone seem to be ranging in the $600+ range (from the little bit of google searching i have done so far).

Or you could use a setup with two accelerometers, which might not work as good but is a lot cheaper.

We are doing a semi-active suspension this year, with the hopes of being able to control US/OS by changing the damper stiffness instead of having to control the brakes (that way we won't slow the car down). The observer part of the control system is going to be somewhat of a "light" version of the ESP, the controlling part will just control the dampers.

Will it work? I don't know.
Will it help us win? Probably not.
Is it fun developing? Hell yeah!

[Dave K]

Anyone know the usual cost of a setup like this?

[screwdriver]

Seems you've got my hints.
1. ESC _brakes_ the car down if it's going too fast
2. requires say an additional braking system or an additional brake actuator
3. to minimize unnecessary slowdowns (see 1) you really really have to know about your car (see Fil's post)

Number 3 is what makes things hard. It basically means you will probably have to implement the system on a legacy car or after quite a long testing-phase.

Regarding why F1 used TC and ABS: They _do_ fulfill the number 3 condition. They can fulfill it because they have the budget to do so and because they work on an evolutionary design.

Generally I think the way to go, if you want to make things faster is what Henning has posted. Implementing TC and ABS once you fulfill all three conditions, will help masking driver mistakes.
After that the handling of the car will again depend from the quality of the conventional car without the control systems. Which passes the ball right back to the engineers again. It means that if the car doesn't perform on it's own, there's only so much you can do with the electronics to counter it.


Regarding the cost issues: I know that Bosch offers their yaw sensors as silicon chips, which should be cheaper than a housed one. Look into that option, if you are planning on building your own hardware anyway.
Our MS4 which supports ESC is well into four digit Euro figures and probably even into five digit Dollar figures currently. At full retail price that is.

[BryanH]

http://www.bosch-motorsport.de/pdf/components/chassis_control/ABS_M4.pdf

Retail appears to be $8k

[rjwoods77]

Hey Guys,

Figured I would throw some resources in case they were needed but it sounds like some of you already figured it out. Here are a bunch interesting papers realted to ABS and yaw stability control. Also to note my friend Tim did his senior design project at RIT by taking his 600cc sprint car, modifying a set of ARS dampers to MR Dampers with the intent of designing a corresponding accel. sensor based control unit that let him tune the cars behavior around the track. Same as the paper I have shows of using MR Dampers to control your yaw stability and let the ABS just control the braking. The dampers worked out good but the control unit was never finished by his lazy team mates. I always thought it would be the way to go.


http://delphi.com/pdf/techpapers/2005-01-1061.pdf

http://delphi.com/pdf/techpapers/2006-01-0923.pdf

http://delphi.com/pdf/techpapers/2005-01-1578.pdf

http://delphi.com/pdf/techpapers/2002-01-0301.pdf

http://delphi.com/pdf/techpapers/2002-01-1221.pdf

http://delphi.com/pdf/techpapers/2002-01-1220.pdf

http://delphi.com/pdf/techpapers/2001-01-0595.pdf

http://delphi.com/pdf/techpapers/2000-01-0107.pdf

http://delphi.com/pdf/techpapers/2000-01-0696.pdf

http://delphi.com/pdf/techpapers/2000-01-0727.pdf

[BryanH]

A little info on the origins of ESC can be read in here
http://www.arjeplogtimes.com/Arkiv-AT08/AT408.pdf

IMHO ESC is a lot more than getting your Nanna home from the shops, One of the sign-off tests involves an emergency lane change around a stationary car at 200km/hr, anyone can do it with ESC on but very few can do with it off. Rumour is that on a dry track a good driver can do faster lap times with ESC off with most cars on the market but that will change.
On an FSAE car it might be easier to use hub mounted brushless motors on all 4 wheels and modulate wheel speed with an ECU only, without the need for expensive/heavy hydraulics, larger brakes etc.
cheers