Linear Pots

[tristancliffe]

Hello. I have one very old, very second hand linear pot that I am using on the front damper of my car. It works, although I'm not sure I'd trust it for tuning dampers or basing too many decisions on it! I'd like to add a couple more for the rear, just to see what's happening. It's not something I'm planning on logging forever, and nor am I hoping to get the best I can afford.

I don't really want to spend £150 + VAT per damper pot (probably around 50mm-75mm stroke), so wondered if anyone knew where to get cheapy ones?

Or perhaps you have a few lying around that you want to get rid of for a small number of coins?

[GORDON STREETER]

Originally Posted by tristancliffe

Hello. I have one very old, very second hand linear pot that I am using on the front damper of my car. It works, although I'm not sure I'd trust it for tuning dampers or basing too many decisions on it! I'd like to add a couple more for the rear, just to see what's happening. It's not something I'm planning on logging forever, and nor am I hoping to get the best I can afford.

I don't really want to spend £150 + VAT per damper pot (probably around 50mm-75mm stroke), so wondered if anyone knew where to get cheapy ones?

Or perhaps you have a few lying around that you want to get rid of for a small number of coins?

A packet of cable ties are cheaper
I jest !

[tristancliffe]

Yes, I've used that technique before on bikes! Sadly it doesn't tell you anything other than peak compression, which may (depending on kerb/grass use!) be more than is actually 'normal'.

[greenamex2]

Good luck, I have spent a couple of years trying to find a usable alternative.

The best I have come up with so far is -

Rotary pots - Fabricate you own 'lever' arms and you can do it for £20 a corner. The accuracy/consistency will depend on how good a job you can do attaching the pot to the chassis and the lever to the suspension (usually a suspension link) whilst allowing enough articulation to not break the pot or arm. One way of doing it would be to attach the rotary pots lever arm to the suspension link using a rod with cheap 'rod ends'. Just make sure you have enough movement!

[sebring115]

Ive used Jaguar or Landrover height sensors before (some cars also headlamp levelling sensors which do the same). They are an active sensor and work quite well, 2 wires for power and 2 for signal. The other alternative are auto gearbox pots, all these are I think less sensitive to dither.

The manufacturer for the sensors is AB/TT in romford and they would be a much cheaper source!!!

http://www.abelektronik.com/

[sebring115]

There are some for sale on racecars direct , just on!! Pi Sensors add.

[Michael24]

The one I'm still looking to do is use the 5v analog Sharp GP2D120 (specs here: http://www.acroname.com/robotics/par...6-GP2D120.html) on car corners or wheel arch corners. Not ideal, but should get you going.

Michael

[tristancliffe]

That's a clever idea, and they look like they're only about £12 each... Presumably they'd ideally need a 'flag' to 'see', rather than just trying to point it at a damper or a rocker. And I could use them for direct ride height measurement if they are able to 'see' tarmac.

And I can buy a lot of them for the price of one linear pot...

[crt]

That is a good starting point. But it doesn't say what update frequency the sensor has?
And also the ouput is non linear.

Take a look at my link for more info.

http://itp.nyu.edu/physcomp/sensors/Reports/GP2D120

[phoenix]

Originally Posted by crt

That is a good starting point. But it doesn't say what update frequency the sensor has?

It does say - it gives a continuous output. So it could be logged at any frequency you prefer.

[phoenix]

Originally Posted by crt

And also the ouput is non linear.

Many automotive sensors are non-linear and need a dedicated table, in the ECU or logger, to translate output voltage to value.

[EfiOz]

Its not an infinite output and the practical update limit is about 20hz. They are good for cheap ride height sensors though.

[YWW730]

I am currently investigating this using an optical encoder as the basis for a string pot. Mechanically these are more reliable and durable compared to rotary pots but is more complex given the quadrature output. I'm just about try an Avago HCTL-2022 quadrature decoder chip to see what comes out

[Paceracing]

Originally Posted by EfiOz

Its not an infinite output and the practical update limit is about 20hz. They are good for cheap ride height sensors though.

20hz is fine for driver input monitoring but next to useless for dampers where the absolute minimum should be 50hz and ideally 200hz.

[Notso Swift]

I think that is what EfiOz is saying, ride height but not shock

...also considering he sells the Variohm VLP in Australia and his business is engine controls, logging and data analysis...

[THR]

Penny and Giles make them and im pretty sure they sell them to people who make telemetry systems.
we use them at work on our machines and have yet to have one fail

[Mwdynamics]

I use these. Penny and giles do amazing kit and never give a false reading!
http://www.pennyandgiles.com/Product...or-MLS130.aspx

[Michael24]

Now you could go cheaper still:

Buy a used ride height sensor from whatever vehicle, as long as you know the pin-outs.
These things are simple angle sensors, but if you mount one on the car near the wheel and extend the arm to an unsprung bit of the suspension, you have a relative named Bob. They output 0 - 5v depending on the angle.

Look on e-bay for "BMW 37140141444"

Discussion here: http://www.autosportlabs.org/viewtopic.php?t=3879

Hope this helps!

Michael

[EfiOz]

That's a good, cheap, reliable option. The only pitfall can be the resolution as the travel they experience on the track is only a fraction of what they are designed to measure.

That can be fixed with some leverage mods though.