Shock position sensors

[zabros2020]

Hey guys,
This may have been covered here before but i looked hard and long and couldn't find anything.
I am planning to use rotary pots on the bell cranks in order to log shock positions. This will be done with little gears of course.
Any idea what the best gear ratio is? and approximate module for the gears?

Thanks in advance.

[zabros2020]

Hey guys,
This may have been covered here before but i looked hard and long and couldn't find anything.
I am planning to use rotary pots on the bell cranks in order to log shock positions. This will be done with little gears of course.
Any idea what the best gear ratio is? and approximate module for the gears?

Thanks in advance.

[Erich Ohlde]

is there any reason you don't want to use a real shock travel sensor?

[J. Vinella]

I think what jayhawk is referring to are know as liner pots.

We tried rotary pots in 05' and testing after comp. Back then we found that they produced lots of "noise." This noise, as pointed out by a professional contact, might actually have been our tires moving. We did also had some problems with the gear wear and the idea was dropped.

This year for testing we are using linear pots because these pots are very easy to retrofit to our current shocks. In terms of simplicity the linear pots are hard to beat.

As to what gear ratio. What information do you want to gain from this system? We have found that looking at this dynamic data in Motec has shown us real insights into our suspension movement and help us to make adjustments in the right direction.

[Mike T.]

In order to get the best data, you'll want to rotate the potentiometer through its entire range of travel as the wheel goes from full droop to full compression. If you've selected a sensor, you know its angular travel range, and you should easily be able to find the angular travel of your bellcrank. With these two bits of info you can easily calculate the ratio you'll need. As for the module, anything available in the proper diameters to fit your application will probably work.

Another thing to consider is that depending on your geometry your calibration will probably not be linear (at different angles the same angular step size will not equate to the same linear step size of your shock) so you will need the capability to input a calibration table rather than a simple constant to get your true shock travel.

[kwancho]

http://jameshakewill.com/sus-pos-v1.pdf
A tech paper written by a friend of ours who races FF. Cheap and simple.

[MSJ]

I've been looking into this too as of late, and although it is definetly possible to use a linear or angular pot on suspension travel, I don't think much will beat an LVDT. Simply due to the non-linearity error in pots if you don't have the R_L/R_C ratio, you can get some skewed accuracy.

That being said though, at this level, who can really afford LVDT's?

[B Hise]

P&G Shock Pots, as used in multiple pro series and available to FSAE at a good price.

Contact:
Eric McDowell
S. Sterling Co.
Office (770)632-8755
Fax (770)632-8756

-Bryan

[Mike Cook]

Yeah, what he said.
Really, if you can afford a daq system, you might as well get good sensors. Buy once...cry once..

[Rellis]

indy uses a rotary

its in the lower left on belcrank
http://lazyfuck.net/uploadfiles/Picture154(Medium).jpg

[B Hise]

Only because of packaging in the Dallara chassis and the "Bart Simpson" gear teeth are prone to wear and have to be replaced from time to time.

For FSAE, use an LVDT.

-Bryan

[GSpeedR]

When you are writing "LVDT" I hope you mean just a linear resistive shock pot and not a linear variable differential transducer, which are really damn expensive.

[zabros2020]

Hey guys, thanks very much for the feedback. Being on the DAQ team i would love to buy LVDT's or even linear pots. But because this is the first year we run a team entriely dedicated to DAQ, i have spent all of our budget on a data logger and other sensors. So you can see out predicament.
I think rotary pots can achieve decent enough results, providing they are set up correctly and the gears are replaced when they wear down.
I am still having trouble with calibration, as someone already mentioned, the table will not be linear, and i was wondering if anyone had osme sort of static test we could apply so that we can calibrate them correctly.
Thanks for all your feedback

[kwancho]

Read the paper that I posted.

[jdstuff]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Ryan Ellis:
indy uses a rotary
</div></BLOCKQUOTE>

Yes, as do many other open wheel cars.....not ONLY because of the packaging on the Dallara.

Also, gears are not the only solution when it comes to rotary pots. I have worked with systems that have small pulleys and ribbed belts that work extremely well. Virtually no wear or backlash to speak of, and quite consistent.

Developing a calibration table is really not too difficult. Essentially, you want to generate two different tables. First, raw voltage vs. rotation angle. This is easy as it should be provided if you buy any decent sensor. Second, you need rotation angle (or rocker movement) vs. damper displacement. For this you'll need a dial indicator or some sort of similar measuring device, and a turnbuckle in place of the shock. Start changing the length of the turnbuckle at known increments and measure the output voltage for each "shock" length. Wah-lah.....instant damper displacement calibration.

[Rellis]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by zabros2020:
Hey guys, thanks very much for the feedback. Being on the DAQ team i would love to buy LVDT's or even linear pots. But because this is the first year we run a team entriely dedicated to DAQ, i have spent all of our budget on a data logger and other sensors. So you can see out predicament.
I think rotary pots can achieve decent enough results, providing they are set up correctly and the gears are replaced when they wear down.
I am still having trouble with calibration, as someone already mentioned, the table will not be linear, and i was wondering if anyone had osme sort of static test we could apply so that we can calibrate them correctly.
Thanks for all your feedback </div></BLOCKQUOTE>

call omega i believe the donate to FSAE teams

[S979]

Some Indycar teams run linear pots on the rears too.

[Pete M]

The big thing to be careful of is crappy pots. A good rotary pot is not necessarily any worse than a good linear pot, so long as you mount it properly and have a decent correction to give you damper position.

Don't assume that a 50c potentiometer will give as good a result as a several hundred dollar potentiometer though. Remember that the info you most likely want is damper velocity, and the differentiation will amplify any noise or jumpiness inherent in the sensor.