Servo gear won't stop spinning and servo horn isn't moving

[bartgojjer]

Hello,

I have an animatronic eye mechanism I built off a tutorial, and one of the eyelid servos isn’t working properly. Whenever I connect it to a servo driver, the motor won’t stop spinning. This is an OSEPP LS 0006 plastic gear analog servo. I can see through the clear blue plastic that one of the gears is spinning, but it seems that it is not connecting to the other gears, and the horn is not moving. When I set the servo to neutral I can get the gear to stop moving.

I’m guessing that this gear or the gear it is supposed to drive is stripped, and the gear keeps spinning because I’m trying to set the horn to a new position, and the servo can tell that the horn has not changed positions. Can anyone say if this sounds like a correct diagnosis? Can I replace the stripped gear if it is indeed stripped? Can I replace it with a metal gear to keep it from stripping again? Can anyone tell me where to get replacement gears for this servo (OSEPP LS 0006 plastic gear analog)?

Thank you,

BenG

[bdaouas]

Hi,

Your diagnosis seems to be correct. If the driver sends a PWM signal to the servo for a position but the last gear (attached to the horn and to the potentiometer) doesn’t rotate because one of the gears is stripped, the closed-loop error will always be higher than zero and the motor will rotate continuously trying to compensate this error. Since sending a PWM signal for a centrer position stops the motor inside the servo from rotating, we can assume that the horn is already in the center position (that’s what the potentiometer is reading) and this confirms our suspicion. You can see the working principle of a servo motor in the attached diagram.
We don’t offer gears for the LS-0006. Standard servos are relatively cheap. You can think about replacing the entire servo as we don’t think it is worth the trouble looking for replacements gears.

[bartgojjer]

Thank you very much for the information!