traction control speed?

[Micko..]

Hi guys/girls

I just had a question about traction/launch control. We are running a ECU that has just had a traction/launch control feature added, they guy who developed it says it will accept a range of wheel speed input of 10Hz to 2KHz. For us to work out how many teeth to put on our sensor we need a ball park figure of what speed the traction control should kick in. at the moment the launch control is an artificial rev limit that is enabled until the clutch is engaged (can put a timer on it).

So I guess the crux of this post is to find out what speed other teams are enabling their traction control?

Does bringing it in too early cause the car to bog down? (The front tyres might not be spinning, or sensor is sensing less than 10 Hz)

Obviously too late means excessive wheel spin.

This will save us heaps of time and money trying different sensor wheels

Thanks in advance http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

[Micko..]

Hi guys/girls

I just had a question about traction/launch control. We are running a ECU that has just had a traction/launch control feature added, they guy who developed it says it will accept a range of wheel speed input of 10Hz to 2KHz. For us to work out how many teeth to put on our sensor we need a ball park figure of what speed the traction control should kick in. at the moment the launch control is an artificial rev limit that is enabled until the clutch is engaged (can put a timer on it).

So I guess the crux of this post is to find out what speed other teams are enabling their traction control?

Does bringing it in too early cause the car to bog down? (The front tyres might not be spinning, or sensor is sensing less than 10 Hz)

Obviously too late means excessive wheel spin.

This will save us heaps of time and money trying different sensor wheels

Thanks in advance http://fsae.com/groupee_common/emoticons/icon_biggrin.gif

[Colin]

Usually you want to use as many teeth as possible to get the resolution at low speeds (important for fsae) but by my rough calcs you could use nearly 100 teeth with that range and still not max out the input. As for this effecting what speed the traction control "kicks in", not sure what you mean here, usually once you have the wheel speed signal to the ecu you set a calibration no. to get the correct speed and the rest is set up in the software, so what ECU are you running?

[Denny Trimble]

Right, I'd say find out the maximum speed you will ever drive the car (we've seen 80mph at local autocrosses; about 70mph in Detroit after the accel finish). Then determine how many teeth will give you 2khz at that speed.

Launch control is very useful for the accel and autocross events. Check out Motec's documentation to see what it's all about.

[Agent4573]

Miko,

Alot of that timing your looking for has to deal with your cars setup and driver. If your running a car with only 40 horsepower and having your driver launch at a low RPM, you won't need to kick in traction control that soon. Now if your running upwards of 70 horsepower and launching right in the powerband, traction control is gonna kick in really soon.

I'm wondering about the wording of your question though. Are you trying to put an actual delay in the system so that the traction control isn't actually on at launch, but comes on later? I would assume you would write your traction control program to be on always, and constantly checking for a signal from the wheel speed sensors. Then as soon as your traction control starts receiving signals, it can decide whether or not to kick in yet.

[Micko..]

hi guys,

thanks for the replys,

Colin, the ECU is called a Dragon fire, the guy who designed it has just started marketing them, we helped him out with the development last year. now he has added a traction and launch control features. traction control is simalar to most other systems, an ingnition cut is used once the front/rear wheel speed differance is past a set limit.

it is the launch side of things i am more interested in. like i said, the ECU uses a rev limiter that holds rpm at a set limit untill the clutch is engaged, we can then set a signal (time or speed) that dictates when the launch control will turn off and the traction control will begin. so what are other teams doing in this sence?????

sorry the origonal post wasn't that clear.

cheers

[MoTeC]

Usually what you would do is change from launch control to traction control a bit before you get out of first. Our launch control only looks at how many RPM you want for a given road speed (un-driven wheels) so you obviously don't want it in play when you go to second gear. The slip control that takes over from launch measures the difference between driven and undriven wheels so it does not really matter if there are gear changes in this mode.

[Frank]

if you're using MoTeC, these files may help


http://www.uq.edu.au/fsae/MoTeC_Traction.pdf
http://www.uq.edu.au/fsae/Traction.xls

[Chas]

I have a few questions concerning timing and frequency error.

How often do you update your wheel speeds? Do you do it fast enough to detect slip within the span of one engine rev? With my specifications, I would like to update the percentage wheel slip every 4 milliseconds but that doesn't seem like an option at low speeds.

What are the uncertainties in your tooth frequency measurements? +- 1Hz etc.?