Stepper Driver Waveforms: Current Control

A bit more data from this setup:

As you saw earlier the low-speed waveform looked reasonably good, although the HB-415M driver produces only 71% of its rated current (so it’s actually 1 A peak, not the 1.5 A in the caption):

The driver runs in 1/8 microstep mode, which means 1 revolution = 8 × 200 step = 1600 steps. Each cycle of that stepped sine wave has 32 microsteps  = 4 full steps/cycle × 8 microsteps. One cycle is about 27 ms, so 1 step = 840 µs → 1200 step/s → 0.74 rev/s → 44 rpm. The Thing-O-Matic runs at 47 step/mm → 34 mm/rev, so this speed corresponds to travel at 25 mm/s, roughly the usual printing pace.

Admittedly, that hairball on the bench isn’t a realistic arrangement, because the motor runs with no load. On the other paw, assuming you’ve done a good job eliminating mechanical binding, then it’s probably pretty close to what you’d see during constant-speed travel.

Cranking the pulse generator to 6400 step/s = 133 mm/s produces this waveform:

The power supply was 24 V, but there was no visible difference at 20 V. The driver evidently can’t control the winding current on the downward side of the waveform. Adding some frictional torque by grabbing the yellow interrupter wheel improved the situation, but not by much.

A box of 2M542 drivers just arrived from a nominally reputable supplier, although they were actually labeled M542ES. Under the same conditions, they produce this waveform:

So there’s something to be said for larger drivers; the HB-415M drivers were operating at their upper limit and the M542ES at their lower limit, both producing close to 1 A peak.