Wheel Travel Sensor Troubles - Linear/String/Laser/???
 

So, this question is actually work related (which will allow me to justify checking MT at work as much as I currently do.)

We are currently using 2x Linear potentiometers on the front of our cars to measure wheel travel on the road and track. They seem to be working well so far. The front suspension is a Strut style suspension and allows us plenty of room and no movement in weird directions.

https://www.miataturbo.net/attachmen...ine=1346982455

The problem stems from our rear end: The string pots!

https://www.miataturbo.net/attachmen...ine=1346982455

The reason that we have been using the string pots is because it allows us to more easily measure movement on solid axles and independent suspension chassis both, using the same sensor. They also move in weird directions which allows us to compensate for axle fore-aft movement/etc. It also has a very small cross section which we feel that we need with some of the IRS setups we deal with where the shocks are run very close to chassis components.

We have broken 3 string pots in the past 2 months just from setup/user error/testing. When a string pot retracts quickly into its housing it snaps off the end, winds up the encoder and breaks it. It is ALOT easier to do then you would think.



So yeah, I broke another string pot today and so...
Do you know of a better way to measure rear wheel travel?

Lasers?

Magic?

I'm just curious to hear if there is anything we have been missing.

Thanks for the help,
-Mike

We use shock pots from I forgot the company but they supply all of NASCAR among other people. They look very similar to your first picture except they have ball and socket joints on the end. For our car I machined custom nuts that were threaded for our shock bolts on one side and the stud from the shock pot on the other. On our fronts that have an extra long shaft extension rather than an eyelet I machined a custom tube clamp for them with a thread on the end. I I was going to make something for a more normal car I would consider using the same (but longer throw) shock pots and making a device that cleared the springs and basically used shaft collars to attach to the body of the shock on the bottom, and then some sort of plate to wedge between the upper shock mount and the chassis up top. For something with a non-coil over shock setup thats much easier since you can just use two of the correct size shaft collar on the two halves of the shock.

Couple super awesome high quality cell phone pictures. I can find any of our high res stuff right now. Here's a solid rear axle solution (sans engine).
https://www.miataturbo.net/attachmen...ine=1346984104

and that front setup with the clamp.
https://www.miataturbo.net/attachmen...ine=1346984104


Another option. Dont measure distance at all, measure force and you can back distance out if you know the spring rate. I think optimum-G has a way to measure force from shock/springs, believe they might use a flat disk type springless forcemeter.

I have a Celesco string pot and I'm happy with it, which one are you using?

Leafy,
I am reading the Optimum-G data acquisition manual right now, I guess I should finish it....maybe this weekend.

Reverant,
Buy stock in Celesco, that is EXACTLY who we are using. I broke a Celesco MT2A today in fact. SNAP. BOOM. $500.

We were measuring the string's response to large displacements....too large apparently. Trying to find the resonant frequency of the string after a quick change in position.

We have been using the Motec I2Pro to measure the frequency response of the Celescos.

If I learn anything fantastic I will try to share it here.


Any other out of the box ideas?

Well obviously enough, if you stretched it more than it can take, boom. I don't know how you can possibly overcome that.

An angular measuring device of some sort?

When I did testing at Harley we used string pots to measure rear wheel travel and never had any issues... but since you are having issues I would just find a creative way to mount some linear pots. Heim joints should let your linear pot move around with weird suspension geometries, or just mount them along the shocks like Leafy did.

You could use lazer beemz. We used them to measure ride height (sortof... its complicated), but I'm guessing they are crazy expensive and I know nothing about what it takes to run them. Our setup required a lot of auxiliary equipment.

This guy had some interesting ideas for measuring ride height. I think he ended up going with some $4 Lincoln part (from the air-ride equipped Continentals and Mk VIIIs) and mounted it at an angle. The whole thread is a good read, I learned more about aero too.

That's a Sharp sensor, I tried to use them but they died pretty quickly on road/track use.

How about ultrasonic fluid level sensors, pointed at the top of the tire?

If they had a low enough latency and sufficient accuracy to give meaniful data I would expect them to pick up the tread blocks on the tires and any rocks or OPR on the tires.