suspension potentiometer, advantageous? 3

[TMSengineer]

I would like to setup suspension potentiometers on our cars to get a better understanding of what is happening with our suspension. However, not having done it before or seen any actual data from them, I would like to ask what the main advantages are, the best way to interpret the data, and mounting practices to follow. They are the linear telescoping type.

Thanks

 

[patdaly]

Check here:

http://www.mtslinearsensors.com/

They are probably the world leader in linear measuring, and in fact, already make linear sensing components for the automotive industry. Check out their low cost line of sensors.
For most of their sensors at least, the output is already conditioned to a linear 0-10VDC.
Hope that helps.

 

[SusTestEng]

"what the main advantages are"

Personally, I would mount the pot in-line with the dampers. Use the information to determine the actual piston speed of the damper during ride comfort events, and handling maneuvers. By knowing the piston speeds of various events, you can help out the damper manufacture tune the damping curve in the exact area you request to improve, by being able to tell them EXACTLY what is happening. In this case you would be measuring velocity, but you can also measure the displacement and use the lever ratio to determine the angles of your suspension links.

Anther thing to try is mount the pot in-line with the control arms. One at each body/crossmember mounting point to check bushing compliance during handling maneuvers.

 

[Uber]

I have some experience with this issue, so I can comment something when you want to measure the displacement and/or velocity of the damper.

First, in-line mounting is accurate and not need to calculate so it will be godd choice, and for this purpose you have to make some brackets to hold the potentiometer, and also the damper, though it may be struts, or just shocks, it will be bend slightly, the upper and lower of the potentionmeter to be connected by rod end bearing.

Second, the potentiometer is easily damaged when you
measure it in harsh environment. You must find a rugged
one to save your money.

 

[SusTestEng]

"the potentiometer is easily damaged when you
measure it in harsh environment."

When I brought this up with our DAQ company we work with, they actually suggest string pots. I know what your thinking...no way. But actually, after looking into some of the string pots available from a company called space age control (

http://www.spaceagecontrol.com

) I think they will work. hey are meant for very harsh environments, and have great load and acceleration limits. I haven't used them personally, but I think they would work.

 

[GregLocock]

We use string pots for this job. They are pretty durable so long as you don't let them rewind all the way under no load.



Cheers

Greg Locock

 

[TravWood]

At a slightly different tangant but still connected. Regardless of mounting what sort of frequencies and velocities would the sensor/shock be experiencing and can most sensors(tele or string) handle this? I realise that a race car would be different to a rally car but what would be approx maximums?

 

[GregLocock]

Good question.

Shock absorber velocities on a race car tend to top out at 2 m/s. On a road car 5 m/s (yes, those are the right way round).

Frequencies - anything above 5 Hz can probably be filtered out if you are interested in handling only.

Cheers

Greg Locock

 

[TravWood]

With a lot of race cars having very low profile tyres(super tourers & DTM etc)and hence higher transmisibilty are there many instances where shocks are seeing much higher freqs that are affecting grip and road holding or upsetting chassis. All this aside what is the expected freq response of most shocks (monotube)or does it depend too highly on valving? ie it maybe only useful to know how high the freqs go in relation to bushes and not shocks?

Thanks

Travers

 

[GregLocock]

"With a lot of race cars having very low profile tyres(super tourers & DTM etc)and hence higher transmisibilty are there many instances where shocks are seeing much higher freqs that are affecting grip and road holding or upsetting chassis."

Depends on what you mean by upsetting the chassis, if you are serious you need to go to 40 Hz - not practical with string pots.

I don't know what the frequency response for tyres is as far as grip goes - but time constants associated with tyres are typically of the order of hundreds of milliseconds. 5 Hz is fine AFAIK.

Shocks will react to frequencies as high as the bushes at each end will let them go - if the displacements are high enough. Typically the bushes provide isolation above 20 Hz, but if you use rod ends (spherical joints), again I'd be looking at 50 Hz or thereabouts.

So my conclusion is if you want to study all the dynamics of chassis supension interactions you'll need eaccelerometers and 40-50 Hz cutoff. if you just want handling then you cn use stringpots or LVDTs, and a 5 Hz cutoff.





Cheers

Greg Locock