Van

I've been very happy with my Traqmate and have been learning how to analyze the data from it. I've decided to see if I can monitor the car's down force. That way I'll be able to see if aerodynamic aids (like CPR's V3 splitter) has a real effect.

They make linear potentiometers to measure shock / strut travel, but these are quite expensive. So, I'm coming up with a cheaper way (that hopefully will work!!).

I've picked up 2 rotating potentiometers ($1.50 each) and will be mounting them above the sway bars. By using a little belt drive system, I'm hoping I can "monitor" the rotation of the sway bars. As the car compresses on the springs, the sway bar will pivot in it's brackets, turn the potentiometer, and I'll be able to measure the amount of rotation.

I whipped up a few brackets - now all I have to do is get some belts and pulleys and wire them up!

I'm crossing my fingers that it'll work.

924RACR

I'd be concerned about rocks getting into a drive belt style system. I'd rather use a ball-jointed linkage - after all, that's what they use on production cars for this app.

Van

Ya know, I didn't think about that!

I started getting parts to do a steering angle sensor (which will be a belt drive on a multi-turn pot...) and then I started thinking about ride height!

924RACR

Have you looked into used factory sensors, then? GM, Honda (Acura MDX) and Ferrari all use the same basic Delphi MR (magnetorheostatic) suspension technology; obviously if you can find a wrecked Cadillac or MR-equipped (F55) Corvette in a junkyard and pull the sensors out, you can save a lot. They put out a pretty typical 5VDC signal that can then be fed into your Traqmate and analyzed from there.

Speaking of data analysis - have you already read my presentation (on my website) about analyzing data? It's a must-read IMO if you haven't already, and are tracking a car with a data system...

2BWise

Another option might be to mount the rotary pots onto the control arms and measure travel that way. Make a little arm extension for the pot. Then mount the pot at the base of the control arm and attach the extension onto the control arm. You'd be measuring the angular rotation of the control arm and can use that to calculate the suspension travel.

Van

Vaughn, I have looked at your presentation, and I have found it helpful.

Bill, I'm hoping to do it this way for a few reasons, first, I only have 4 analog input channels on the Traqmate - so it would max out my data acquisition to measure each wheel independently. Second, by measuring the sway bar rotation, I get to measure when "both" control arms move in the same direction - a kind of "smoothing" or "averaging" effect. Third, I can change my "lever arms" and amplify the movement of the potentiometer - and that will give me greater resolution. If the pot was at the pivot point of the control arm, it would only move a minuscule amount, so precision would go down.

Make sense? Or have I spent way too much time thinking about this?

924RACR

Actually, grabbing it in the middle of the swaybar would indeed make sense and achieve what you're after - an averaged ride height per axle - and that will be more useful for looking at downforce impacts. Just have to zero it out if anything's moved.

2BWise

Makes sense. I'm just curious if you'll see any large enough changes to actually be able to make a firm conclusion on downforce numbers without any serious wings. I have a feeling the changes will be miniscule. The thought for pots on each control arm gives you a bit more than just ride height, but shock speeds which can then lead to further shock tuning later. Just seems that you'll be able to do more with pots at each wheel.

Van

The rear is 2" from the center (because of the exhaust, I can't do it right at the center).

In the front, the oil pain is the only thing by the center of the sway bar... I figured that I'd be best mounting the pot on the solid sway bar mount, although it'll be biased towards the movement of one wheel.

No doubt individual pots at each wheel are best - but they come with a price... a price I can't justify right now. Hopefully my method will work, but, if not, I won't be out much money - just a few bucks.

Cory M

Van - it looks like the arm on your front sway bar is about to fall off! I have the same Tarett bars and mine are set up so that the splined shaft end is flush with the arm, it looks like you've only go about hallf the contact. I'd fix that before you head out on track again.

Van

Mine are offset about 1/8" - I was getting a little binding of the ball joints when I have the ends flush. I've run it that way for 7 or 8 years and never had a problem.

I finished installing my sensors. Got my pulleys on and got them wired up. Will the work? Don't know yet - but testing with a multimeter shows that the resistance changes about 0.04 ohm for .1" of wheel travel....

Van

My sensors worked very well! (i.e. they gathered data that looks pretty cool...)

Here are 2 laps at Lime Rock from yesterday. In these charts, the top graph is braking and acceleration G forces (when the line goes above zero, I'm braking, when it goes below, I'm accelerating). You can see the "segments" on the track map and how they correspond on the graphs.

The middle chart is the front ride height sensor - as the line goes up, the body is going up, meaning the suspension is being unloaded. As the line goes down, the suspension is compressing.

The bottom chart is the rear ride height sensor, but its data is going the other way. As the line goes down, the suspension is unloading.

You can see how weight transfer takes place as I'm on and off of the throttle. And, for those that know Lime Rock, you can see how the suspension compresses on the uphill turn, then decompresses at the crest of the hill!




Now, I have to put on Patrick's V3 splitter and see how the #s change!

coonabarabran

Have you continued to measure this? Any improvements or otherwise in the method? I'm interested in trying it, thanks.

Van

Yes! It's a different car now... and the sensors are different...

Jeff951NJ

Cute, your old suspension setup. It looks a little more fancy under there now.