I built a test jig to experiment with a friend’s 16-pin A4988 stepper driver, and even added bi-directional LEDs to the outputs and, regular LEDs to the inputs, to see if it behaved as expected.
By default, it does a full circle in 200 steps, and both coils were always driven. Fine. If MS1 is set, every other step features a coil off. 200 steps rotate it half-way. Expected.
But in any jumpered “microstep” mode, and pulsing VERY slow, I can see and feel that it MERELY COUNTS steps, before the last two. For instance, at Sixteenth Stepping, the first 14 steps do nothing whatsoever. Step 15 advances a half-step, and Step 16, the next full step.
No PWM, no fractional voltages. Just counts until the final two steps, and half-steps.
So I ordered a pair of LV8729 controllers of the same 16-pin RAMPS-style from BigTree on Ali. Certainly these would microstep … but no. Precisely the same behavior.
Anything above half-stepping, they just count until the final two pulses in the sequence. No modulated PWM, and no in-between. Half-stepping is the finest resolution available.
Does anyone have the same experience? Is there some secret to force this style of stepper driver to do real microstepping?
Have found no online references to fake microstepping on cheap stepper drivers. It is hard to imagine that millions of these are being sold, without true PWM fractional steps. Someone would notice, eh? At regular speeds though, it is difficult for a human to see.
- 1You need to observe the drive waveforms. It may be cheating as you say, or it may be that stiction and pole shapes make for non-linear torque (cogging) specific to the motor, so the first 14 steps don’t move anything. – user_1818839 2 days ago