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Motor works at 1/16 microstep, but not at 1/2, 1/4, 1/8?

Posted by 3dflat 
Motor works at 1/16 microstep, but not at 1/2, 1/4, 1/8?
May 24, 2017 02:48PM
I was trying to find the maximum step rate I could drive my extruder NEMA 17 motor (for fast retraction, basically).
I thought using 4 microsteps would afford ~4 times faster speed than 16 microsteps.

What I found instead was surprising: at 1, 1/2, 1/4, 1/8 I could stop the motor with my bare hands, no matter how low the speed was. Only at 1/16 it started working reliably.
The second thing that surprised me was there being no gain in speed: the motor made weird sound and skipped steps at approximately the same speed, as if microsteps did not matter.
Two other motors made me scratch my head even more: a "high torque low current" NEMA 17 showed the same behavior below 1/16, except its maximum stable speed was 2/3 that of the stock motor.
The third motor was Qunqi NEMA17 from Amazon, and it was going strong with every microstep setting, but also maxing out at what turns into 30mm/s at my extruder.

What am I missing? Why don't I see increase in maximum step rate and speed when I lower my microstep number? Why a motor would work at 1/16, but provide almost no torque at 1/8?
Controller is MKS Gen 1.3, drivers are LV8729, Vref is 0.4V (resulting in 0.8A per phase).
Re: Motor works at 1/16 microstep, but not at 1/2, 1/4, 1/8?
May 25, 2017 12:08AM
I'm using retraction of 80mm/s with my RAPS128 drivers in 1/64 stepping mode. I wonder, how fast you want to retract?
VDX
Re: Motor works at 1/16 microstep, but not at 1/2, 1/4, 1/8?
May 25, 2017 01:22AM
... could be, the step pulse length is so short, that it won't be detected reliably ...


Viktor
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