How Do You Determine Potentiometer Resistance Rating?

[markrvp]

I've got a couple of Happ pedals I want to hack to a Fanatec Speedster 3 XBOX wheel.  I figured I needed to determine what POTS are in the Fanatec pedals now so I could put the same resistance pots on my Happ pedals.

Can someone tell me how to determine this?  I assume they are either 100k or 50k pots.

[NoOne=NBA=]

Individual pots are pretty simple.
You usually have leads connected to the two ends, and one in the middle that varies.

A---------B---------C

The easiest way to determine the center tap lead (other than it's USUALLY the center one) is to move the pot all the way in one direction, and measure resistance.
One set of two should be close to a dead short, and the other should measure close to the full resistance.
As you move the pot, the resistance should vary between the two formerly shorted leads.
When it hits the other end the remaining pin should be shorted to one of the first two.
The pin that shorts to another at both ends is the center tap (B in the diagram above).

With the pot all the way to the left above, the resistance from A-B should be 0, and the resistance from B-C should be the value of the pot.
A-C should remain constant regardless of movement of the pot, and is the actual value of the pot.
As the pot moves right, A-B will climb, and B-C will drop, until A-B is the value of the pot, and B-C is zero.

Another factor in this is restrictions to the physical travel of the pot.
If you have a 100k linear pot that travels 180 degrees, but is physically restricted to only half the available travel (90 degrees) the actual useful resistance range will only be 0-50k.

Yet another factor to keep in mind when measuring is that the pot shouldn't be connected to any other circuitry.
If the pot is connected to something else, it can cause a false reading due to reading the resistance of the entire circuit, rather than just the pot.
The easiest way to do that is to cut the leads to the pot, and measure directly to the leads.

With all that in mind, pedal sets can still be a little tricky.
The logitech set I've got is actually wired together, so that it is one big pot.
If you press the gas pedal, the Y-axis climbs to maximum on the joystick calibration chart--depending on how far you press it.
If you press the brake pedal, the Y-axis drops to minimum.
If you press BOTH pedals to different depths, it reads the difference between them, and acts accordingly.
If you fully depress both pedals, it reads it like no input because it is going fully up and fully down at the same time.

And lastly, if you find out the pots in the current pedals are 100k, and use all 100k, you need to make sure that the Happs pedals are able to output the full 100k range as well.
If the original pedals didn't have anything restricting their movement, and the new pedals do, you will not show the full range of motion you need.

[markrvp]

Thank you very much. 

[ahofle]

With all that in mind, pedal sets can still be a little tricky.
The logitech set I've got is actually wired together, so that it is one big pot.
If you press the gas pedal, the Y-axis climbs to maximum on the joystick calibration chart--depending on how far you press it.
If you press the brake pedal, the Y-axis drops to minimum.
If you press BOTH pedals to different depths, it reads the difference between them, and acts accordingly.
If you fully depress both pedals, it reads it like no input because it is going fully up and fully down at the same time.

Horrible!! How are you supposed to perform burnouts while stopped at a traffic light?