Curious Motor Phase Errors

fcwilt

Hi,

I was fitting a new NEMA 11 stepper to a printer. I was short on specs so I chose some config values I thought were safe.

M92  A3200    ; steps per mm (3200 for 1mm lead)
M203 A1200    ; max speed (mm/min)
M566 A900     ; max instant speed change (jerk) (mm/min) (defaults 900)
M201 A500     ; acceleration (mm/s^2) (defaults 500)
M906 A500     ; motor current (mA)

I started testing with a slow speed (F100) and it worked fine. I increased the speed to 300, 600 then 1200.

The movement and sound from the stepper was fine at all speeds but at 1200 I got these warning message:

Warning: motor phase A may be disconnected reported by driver(s) 4
Warning: motor phase B may be disconnected reported by driver(s) 4

Dropping back down to speed of 600 and no warnings.

Any ideas why the warnings would be speed related?

Thanks.

Frederick

dc42

@fcwilt you may get those warnings at high speeds if the back emf of the motors at those speeds is higher than the VIN voltage of the Duet. See https://www.reprapfirmware.org/emf.html.

fcwilt

@dc42 said in Curious Motor Phase Errors:

@fcwilt you may get those warnings at high speeds if the back emf of the motors at those speeds is higher than the VIN voltage of the Duet. See https://www.reprapfirmware.org/emf.html.

Inductance appears to play a significant role in generating back emf.

So I need to find the specs or perhaps a way to measure the inductance of the stepper.

Thanks very much.

Frederick

o_lampe

@fcwilt
Knowing the inductance of the motor won't help making it faster.
I'll soon test external TMC2225 drivers which are suitable for 36V and 1.4A. Just right for those geared extruder motors (or my hitchhiker IDEX motor)
Most external driver boards have 35V capacitors and separate Vin...

fcwilt

@o_lampe said in Curious Motor Phase Errors:

@fcwilt
Knowing the inductance of the motor won't help making it faster.
I'll soon test external TMC2225 drivers which are suitable for 36V and 1.4A. Just right for those geared extruder motors (or my hitchhiker IDEX motor)
Most external driver boards have 35V capacitors and separate Vin...

I understand that. But knowing the inductance and comparing it to other steppers that don't exhibit this problem might teach me something.

I did find some specs of a sort, but being a product out of China you never know how good the specs are.

In any case the stepper is "rated" for 24 volts and I was using it on one of my first printers back when I was using 12 volts and I have never taken the time to update the printer.

Frederick