[FTC]: Servo has parkinsons???

Other FIRST Tech Challenge
1

Has anyone else had issues with the 180 servos twitching out? We have 2 on our bot, 1 twitches for 5-10 seconds every time we drive the bot, bu the other does not. We have swapped out the twitchy servo and still have the same prob.

thanks

  • Team #3787 “The Green Exploding Volcano Monsters”
2

We’ve had the same problem, might be an issue with the mechanism its attached to causing constructive harmonic interference (in other words, the servo corrects its position at the same frequency the mechanism sways/bounces/oscillates). If this is the case, mechanical dampers (such as a plate in contact with the mechanism to slow it down due to friction) might help.

3

I was told it is an electrical problem, between your motor/servo control boxes.

4

This right here is generally the correct answer. The servos that you guys use in FTC are similar to that found on RC cars and planes. I have observed in both of these the “twitching” that you described. Every time I have been able to correct this simply by putting rubber washers in the mechanism and tightening it until the jitters stop. Any other form of stabilizing mechanism works too.

Before you do this, I will warn you that any kind of drag on the mechanism will cause inefficiencies. If you need the speed or the full strength of your servo to do the job, don’t do this. Also, putting too much drag on the mechanism could cause the servo to overheat.

My recommendation: If the jitters in the servo don’t affect anything, ignore them. There’s likely nothing wrong with the servo and messing with an already working mechanism can screw things up.

5

We have also had this problem before. In most (if not all) cases it can be traced back to a DC motor. Our guess is the brushes on the motor start wearing (or possibly a short in one of the windings) and causing electrical noise. Once the offending motor has been replaced, the problem goes away.

6

Two possible issues here…

  1. The servo is not firmly mounted in place. As the servo moves in it’s mount, it may over shoot it’s target.
  2. If the servo wiring is running close to motor wiring, the noise generated in the motors may be picked up by the servo wiring and interpreted as a command. Try pulling the motor wires and then operate the servo to check if it jitters.
7

Excellent suggestions everyone. We’ll try in this order and let you all know what works…

  1. Check servo mounting to make sure its secure.

  2. Move servo wires away from DC motor wires - Right now they are all bound together with zip ties.

  3. Check all DC motors to make sure they are working correctly (as much as we can).

  4. Ignore it.

  • Team 3787
8

We are having a very similar issue. Ours will work fine while running a prototype test in labview, but when we deploy our code to the brick and attempt a teleop our servos jitter and then go nuts for a few secs and then become non-operational. Has anyone ever experienced anything like this?

9

There is a known Servo problem with the LabVIEW code that was included in the latest main update. Here is an earlier post I made regarding the patch.

Phil