Mounting damper travel sensors

[povelocj]

Hey all, I was wondering how other teams went about mounting damper travel sensors. Our dampers mount to 1/4 in bolts and our linear potentiometers from from Pi have size 10 rods connections. I need some sort of shouldered bolt to connect the two. I'm looking for something like in the attached picture.

http://i52.photobucket.com/albums/g14/povs9/dampertravel.jpg

[SNasello]

Those screws are definitely custom made, looks like they are titanium also. A very good way to mount a potentiometer.

[carbon_black]

We drill out some hex bar, tap a thread and run a threaded bar/screw/bolt through it. It then sits on the two exposed threads that we need for tech. Never had an issue with it.

http://i.imgur.com/2vvU0.jpg

(We use the Penny Giles SLS ones, though they are pretty fragile)

--

UTS Motorsports
Sydney, Australia

[SamB]

It's all about the custom made bolts! Turn a shoulder then drill and tap M3. Looks pretty sexy if you ask me...
https://lh6.googleusercontent.com/-3qbcvOQbnvU/Tgr_Vdk6yqI/AAAAAAAABhs/onRR3wa6okk/lin%252520po.jpg

[Charlie]

Good solutions, but don't think you need to mount the pot directly to the shock bolt. You can mount it just about anywhere, and calibrate it to shock travel. Rotary or string pots can work too.

[sbrenaman]

Be careful if you don't mount them directly to the damper bolts. You can calibrate for full droop and full compression, but if the motion ratio curves are different you can have misleading results.

[Charlie]

Originally posted by sbrenaman:
Be careful if you don't mount them directly to the damper bolts. You can calibrate for full droop and full compression, but if the motion ratio curves are different you can have misleading results.

Anyone designing a FSAE suspension should know better than to calibrate a displacement sensor at just two points... but your point is probably worth stating I suppose.

[woodsy96]

I'm curious to see what other teams do who have a similar problem as us- our damper pins aren't in plane. I'll get some pic up of ours shortly.

[nstrahan]

Anyone designing a FSAE suspension should know better than to calibrate a displacement sensor at just two points... but your point is probably worth stating I suppose.

Just curious. Can't you come up with an exact solution for this? For our car this year mounted our pots to the push rod joint and the tab on the frame. I came up with an exact relation between shock travel and damper travel. It was complicated (lots of law of cosines) but I think it is correct. Will this method work? Is there something inherently wrong with this approach?

[Claude Rouelle]

1. Good idea to mount the linear potentiometer on the same mounts as the damper. I have see too many guys working on their car on stands, disconnecting one damper mount, seeing the non suspended mass falling down and having two half linear potentiometers for the price of one: they are not infinitely telecospicable. A linear potentiometer is not a droop limiter.

2. The difference between mounting the sensor on the same mounts as the damper and one one point of the damper and on the chassis (even if you calibrate it properly vs the damper length variation).... is called compliance.

3. Make sure the linear potentiometer stroke is just slightly bigger than the damper stroke. A few years ago I had on an indycar both a linear potentiometer on the damper mounting point and a rotary potentiometer on the rocker (too long to explain why and that is not the point anyway) . The issue was that the maximum damper stroke was about 80 mm while the linear potentiometer stroke was 100 mm. Fine. But the rocker full movement was 27 degrees while the rotary potentomer maximum angular movement was 330 degrees. Did you say resolution?

4. Just calculate 12 bit (for example) = 2^12 = 4096. 100 / 4096 will tell you the minimum movement of the linear potentiometer to see something on you dta

5. Linear potentiometers are variable resitance; you need more than 2 points to calibrate them

[jd74914]

Just curious. Can't you come up with an exact solution for this? For our car this year mounted our pots to the push rod joint and the tab on the frame. I came up with an exact relation between shock travel and damper travel. It was complicated (lots of law of cosines) but I think it is correct. Will this method work? Is there something inherently wrong with this approach?

There is nothing wrong with your approach, just a caveat. While you can come up with an "exact" solution, the accuracy problem is due to build and component tolerances. During build all of your points will move a finite, but generally unknown, amount. Calibrating after installation reduces error due to build tolerances or math mistakes. Doing the math first verify the selection of your frame mount is good, but it's best to check this number with an actual measurement. Another good reason to check calibration is that linear response isn't guaranteed from your pots.