Nema 34 stepper motor broken - lost its holding torque

[skimbeh]

Hi everybody,

For a project, I use big 34HS1456 stepper motors (Datasheet). They were working fine in my setup, but there was an unexpected big load on the motor. Since then the motor lost its holding torque. Normally when energized, I can not move the axis at all. But since the 'accident' the shaft moves when it has to hold a small load still...

Does anyone know what happened with the stepper motor? And is it fixable?

I use two of the same motors in the setup, and the other one works still fine in the same conditions.

EDIT: The driver that I use: ACT DM860 that can handle up to 7.8A. I have it set to give a peak current of 5.7A (which matches the stepper).

Would love to get some responses and thoughts

[zwieblum]

Stepper driver broken. Try swapping.

[skimbeh]

Thanks for your response zwieblum, I've changed the motor driver and power source, and the same problem still occurs...

The driver that I use: ACT DM860 that can handle up to 7.8A. I have it set to give a peak current of 5.7A.

I noticed whilst testing that the motor lost overall torque, not only the holding torque. Any ideas?

[zwieblum]

All torque sounds a bit unhealthy. Is a wire broken?

[skimbeh]

From the outside, I can not see any faulty/broken wires. For now, I don't feel comfortable in opening up the motor since I've read that it can harm the motor even more...

I'm powerin both moters the same way, but the 'broken' one has 1/10 of the torque atm

[zwieblum]

You do not need to disassemble the motor. Disconnect it from the driver,  measure resistance & inductivity for both coils. Compare the values with the datasheet or with another motor.

[skimbeh]

Both the coils give me a resistance of 0.6 ohms, which is correct according to the datasheet! I'm not sure how to measure the inductivity of the stepper...

[zwieblum]

Just to confirm your test:

powersupply A --> stepperdriver A --> motor A : motor A is NOT OK.
powersupply A --> stepperdriver A --> motor B : motor B  is OK.
powersupply A --> stepperdriver B --> motor A : motor A is NOT OK.
powersupply A --> stepperdriver B --> motor B : motor B is OK.

Did you test these 4 setups?

[Robin2]

Both the coils give me a resistance of 0.6 ohms, which is correct according to the datasheet! I'm not sure how to measure the inductivity of the stepper...

My guess is that if the resistance is correct there is nothing wrong with the motor.

Your earlier description " but there was an unexpected big load on the motor." is not something that would cause damage either to the motor or the driver (assuming you mean a mechanical load).

...R

[MarkT]

The rotor is slipping on its shaft I think - is this a cheap/budget motor?

[skimbeh]

Oh my.. I found the problem. Since I am prototyping I am using 3d printed PLA gears. The 'unexpected load' damaged the contact point of one of the gears. So the gear slipped on the shaft, which gave the impressions the holding torque of the motor failed.

Thank you for the support though guys

[MarkT]

A NEMA34 motor definitely needs steel gears, they can generate several Nm or torque.