Inventables Community Forum

Stutter from servo when pulling any axis

Hi,

My X-carve was out of square and had all kinds of problems that I’m fixing, but I noticed this stutter from one servo when pulling the gantry “a bit faster” along the Y while powered off. The right side noticeably jumps when doing this.
What’s more, it that servo seems to “react” by sounding/vibrating even when pulling along X-axis, see video #2.

Right side stutter when moving in Y
Right side servo stutter when moving in X

Is this normal / expected behaviour? If not, what could it be?
I’m afraid that these “jumps” might be the reason why I sometimes get catastrophic failures (diverting off track).

There is an old phrase, if it hurts don’t do that.
They say moving the machine manually can damage the stepper drivers.

Sounds reasonable. I thought however that it is expected that some manual “feel” is applied to check the tension of the wheels / that there are no bumps. But maybe all motors are expected to be disconnected when doing so?

You won’t hurt the servos, However, the servos will actually act as generators if you move them manually. Then they have the possibility of sending a current back to your controller damaging it.

I am aware of that. Disconnecting the servos was meant to protect the drivers.

Technically speaking, we dont use servo, but stepper motors. Servo motor is a regular DC-motor with encoder to monitor speed/position and dont have the magnetic detents as a stepper motor have. Hence “stepper” and typically 200 steps / revolution.

Dont read this as nit picking, purely as informational :slight_smile:

@JWAM_Shop are you having issues when you carve, or is just happening when you manually move the gantry?

Sorry, of course I meant steppers.
Your comment in itself is just fine, but the total amount of comments start to make it seem as we are actively not trying to talk about the actual question at hand. :slight_smile:

I’m specifically asking whether or not they behavior electronic-wise is expected, or if I have some driver/stepper issue somewhere.

I’m not sure as I’m currently in maintenance mode. When everything is back up, I’ll try running it fast and see if I hear/see such behavior.
It should be easy for someone else to check whether this happens to them or not / someone with knowledge might be able to tell why this occurs. Certainly something is driving/braking here, and it is interesting that it seems to happen across different axis. At least that’s how it feels.

No worries, I read through the replies and it seemed you were guided the right way already and I didnt have more to add on that :+1:

There are several things that I am aware of that can cause your problem.

  1. it is possible that resonance is cropping up, either in the motor, the belt, or the carriage.
  2. low power to the steppers. It is possible that you are running them with a current setting way too low.
  3. There is the possibility of binding of the moving parts on the track.Without the belts connected, the carriages should move very freely the entire length of motion.
  4. you could be driving the steppers with too high a frequency. For most hobby systems a clock frequency of 25 kilohertz (25KHz) is plenty fast.
    This can be calculated by knowing how fast you need it to go and calculating the number of steps per second you need. Clocking at too high a clock speed sends too narrow a pulse to the stepper drivers and pulses get lost.
    Good Luck,
    Pixel