bump in drive system...?

[REVCAM_Bob]

Wondering if this might ring a bell with anyone.
I have a 1kw motor hooked to a drive, by the way I have what I feel are 2 identical systems..... One works just fine, the other so so.
With identical tuneing parameters on each, one motor runs smooth, the other
does this bump thing.... as it rotates at low rpm, once each turn, always (i think) in the same place, it hesitates or jerks, it is hard to tell which, I can here it and feel it if I place my hand on the motor. I have rechecked the 6 combinations of motor hook up and this is the only one that "works".

Does this sound like anything any of you have run in to before?

Thanks, -B

[HuFlungDung]

This is on a servo system not a stepper?

Is the axis smooth to turn over manually (with the power off). I'm thinking of a bad bearing, or a bent shaft which would produce a tight spot.

Other than that, I'd suspect a defective encoder, bad cable, bad shield, or perhaps a loose coupling between motor and encoder which would create a spike when position is momentarily discerned by the controller to have strayed, which creates a large 'position error' which the servo attempts to recover from. It happens so quickly that it appears as a bump.

It might even be a bad winding on the motor.

You should be able to isolate the problem between amp, motor, and cable by selective swapping of components. Remember to keep the motor and encoder combinations together to prevent runaway, or the safest method, disconnect the motors from the machine for testing.

[unterhaus]

a bad commutator bar will cause this at low speeds. If moving it by hand with power off doesn't show anything that might be the problem.

[REVCAM_Bob]

I'll check out turning the motor by hand, I can also swap drives cables etc.
I can swap encoders also, this should help narrow it down.

Yes it is a servo system....