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[paul_astrix]

I built the Astro EQ PCB a few years ago - the interface chip is labelled "AstroEQ-USB 27/03/17" I used DRV882x drivers, allegedly from Pololu. The latest firmware was downloaded/uploaded yesterday.

On Sidereal tracking (32 steps) the motor steps forwards, then backward, then forwards, then backwards.......oscillating forever. Different motor current settings give different movements, but it always oscillates.

Sidereal with 1 step and 4 steps also oscillates.

Slewing oscillates, but at 800X the motor will spin. However it can spin in the other direction during the next slew! The direction of 800X spin seems to vary according to where it stopped. Also it oscillates until the software has ramped up to almost full speed, then it spins.

I wonder if I have cooked the motor? It did get very hot, then I realised the wiring was wrong and I may have had the two phases in series for a while. OOps  .

Perhaps the driver(s) is damaged? 

Would current/voltage limiting in the power supply cause oscillation? It is rated at 1A, but I have not measured the voltage when the motor steps.

Something is very wrong, as the motor is not under load. I'm testing it on the workbench with a bit of tape on the shaft.

I wonder if a stepper motor test circuit is worth building? I think I have an L293 shield for the Arduino somewhere.

Any help is appreciated.

[TCWORLD]

Stepper motors are quite resiliant.

Have you wired the motors up correctly now?
You should wire them to the RJ45 connectors as:  xABBAx - where x is no-connect, A is one coil, and B is the other coil.

If you have it connected as xABABx, you will end up with the oscillation behaviour you describe. This won't damage the motors, but it will cause weird behaviour until corrected.


Once you have checked your wiring, make sure to adjust the current limit, then try again. If the motors are getting hot, try reducing the current limit.

[paul_astrix]

Thanks Tom,

I checked the wiring and deduced xABABx was correct for the RJ45 by looking at the schematic. The labelling is:
RA_1B
RA_2A
RA_2B
RA_1A
which I assumed was coils A and B, connections 1 and 2. 

However your reply, correct I'm sure, implies coils 1 and 2, connections A and B. Brexit is clearer ha ha 


I ran a quick Arduino + motor board test (https://www.instructables.com/id/Stepper-Motor-Test-With-Arduino-Using-Arduino-Moto/).  The motor rotates smoothly on 5V supplied by my laptop, on all 4 stepping modes, slower RPM on micro-stepping. But on 12V it runs rough and stutters a bit on the DOUBLE setting.

The Nema 14 motor ratings are:
Phase current 0.8 A
Phase resistance 6.8 ohm
Phase inductance 10 mh
Rated voltage 5.4 V

The shield driver runs hot on 12V, too hot. The rough performance maybe current saturation in the switching supply limited to 1A

I'll rewire the motor correctly for the AstroEQ and report back.

Many thanks,
Paul

[paul_astrix]

Tom,

Update: I've just realised there are different pin-outs for A498x and DRV882x. But I had assumed they were compatible, and did not notice the "Pin name format" comment.

-Paul

[paul_astrix]

Everything seems to be working well now. Best setting for my motors are:

Step Modes: Slow = 8 usteps/stp,  Fast = 1 ustep/stp

With no load, the fastest rate without stalling is 650x

-Paul

[TCWORLD]

Glad you're up and running.

And yeah, the labelling of the coils is really awkward - some manufacturers use A/B for coil and 1/2 for the ends, others use 1/2 for the coil and A/B for the ends.

I've updated the AstroEQ FAQ to add this information.


Kind Regards,
Tom.