[ez-cnc.com]

Hello, im worknig in a custom machine to wind bass guitar pick ups. Im trying to have a stepper at 5 RPS(well its selectable from 1 to 5RPS). It has an acceleration till it gets to 5RPS. When it gets to 5 rps it takes about 3 or 4 seconds to stall(i thinks its the right word, i mean the motor stops). It does a a kind of a progresive sound till it stops. If i load the motor a bit(with my hand) it wont do it and it will keep turning, if i let go it will take 3 or 4 seconds and it will stop. Wierd thing is that its also doing it at 5, 4.5, 4, 3.5, 3, 2.5 and 2 RPS. Its stable at 1.5 and 1 RPS.
I think it could be resonance problem. But im not sure.
Anyone has ever runned accross something similar??
The driver im using is a l297 l298 with a nema 23 motor.
Thanks, Matias.

[Mariss Freimanis]

That is mid-band resonance. The motor makes a descending growling sound, then stalls.

Mariss

[ez-cnc.com]

Is there a way to avoid it??? In the begining it didnt do it. What surprises me is that now it is doing it at a really low speed.
any ideas or suggestions???
Thanks, Matias.

[ez-cnc.com]

How could a new motor work fine girst and then have this resonance problem.
Any places where i can find mor information???
Thanks, Matias.

[Mariss Freimanis]

Mid-band resonance is a motor behavior. It is most severe between 5 and 15 revolutions per second.

Being a resonance, something has to trip it off. It's always there, hiding until something triggers it. That "something" is a load torque disturbance (an abrupt load change).

Here's how you can test a motor / drive for resonance:

Run the motor at 600RPM lying on its side on a hard benchtop with no load attached. Pivot the motor up from the benchtop 1/2" using one corner of its mounting flange as a fulcrum. Rotate it back down with a sharp bang onto the bench surface and press down firmly on the motor. The motor should immediately breakout into resonance and stall in a second or two.

Drives that have midband compensation circuitry will not resonate.

Mariss

[ez-cnc.com]

Thanks Mariss, u have been very helpfull.
I tried with another motor and it works just fine even at 10RPS.
Now the question is, why a new motor that worked fine at 5rps now it cannot even rotate at 2 RPS. Cuold it be that it got demagnetized or something like that, cause right next to the motor i had the transformer.
I dissasembled the motor and the rotor doesnt have a strong atracction to metals, in other motors i dissasembled it was stronger.
Hope someone can help withs this doubt.
Thanks, Matias

[Mariss Freimanis]

That is a more serious mistake. Never disassemble a step motor and remove the rotor from the stator. Doing so demagnetizes a motor.:-(

I ran some tests on that a few years ago and posted the results on the CCED group. The test was to run dyno tests on a motor to get a baseline, then disassemble the motor, remove the rotor and immediately put it back in and reassemble the motor.

The motor had less than 50% of its original torque when it was re-tested on the dyno. It was demagnitized in the few seconds it was removed from the stator which acts as a magnetic "keeper".

Mariss

[pminmo]

ezcnc, did you dissasemble the motor before you had the problems?