SparkFun Forums

[radioactivqted]

I modified a servo to use an external potentiometer so that it would read the position of an output shaft (on the other end of a gear train). However, the servo now does not seem responsive to the potentiometer, instead just rotating constantly in one direction. Would I need the original potentiometer for this, or would any potentiometer work?

[Ross Robotics]

What potentiometer?
What servo?
How is it connected? A clear pic or schematic is preferred.
I would think that a cheap DC motor and pot would have been better.

[radioactivqted]

The servo: https://www.sparkfun.com/products/11965
and the potentiometer: https://www.sparkfun.com/products/9288

I don't have access to the system right now, so I can't really provide a super accurate description, but I can get this soon. Basically, I desoldered the wires that went to the original servo potentiometer and soldered on the wires to the new one.

[markaren1]

Try swapping the end wires to the pot, it night be wired electrically/mechanically backwards

-Mark

[radioactivqted]

One thing that I did notice was that the original servo potentiometers worked just fine, even with the same wiring. Why would that be a factor here?

[lyndon]

Did you measure the resistance of the original pot to be sure it was the same as the replacement and also check that they were wired the same way?

[radioactivqted]

I measured the pot and it had a resistance of 5k (and got some new 5k potentiometers). However, it seemed like there was something weird with the wiring - the wires that normally would go to power and ground actually seemed to be connected the wiper somehow (?). Are the pins on a servo potentiometer set up differently than the "normal" setup with the wiper at center?

[lyndon]

I measured the pot and it had a resistance of 5k (and got some new 5k potentiometers). However, it seemed like there was something weird with the wiring - the wires that normally would go to power and ground actually seemed to be connected the wiper somehow (?). Are the pins on a servo potentiometer set up differently than the "normal" setup with the wiper at center?

Not that I recall, but it's been a long time since I took one apart.

[radioactivqted]

This is a bit late, but I replaced the potentiometer with a new 5k potentiometer (the original was also 5k). However, the servo still seems unresponsive to its position. Could this be because of the fact that the original pots had 220 degree rotation, whereas the new ones have something more like 300 degrees? Should that even make a difference?

[radioactivqted]

Upon examination of the hardware/code, I think found the problem. It looks like I forgot to change the pwm values going to the servo, so it wasn't using the whole range of the new potentiometer. Another one of those moments... Thanks everyone.