The motor is used in a slightly different scenario, it runs a shaft which acts a bit like a spindle driven via a pulley / belt at 2.67:1 ratio. The load is pure friction on the bottom of the 'spindle', this is variable really and it's really hard to define what the max / min is. So far I've done the following:

- had an 8Nm stepper mounted, running by mistake at 480RPM. This would sometimes stall at full speed (480RPM), a lot of hit and miss, sometimes it was stalling at ramp up. I've only just realised that I was generating 3200Hz to the drive, yet the drive was set to 400 microsteps which gives 480RPM, I was really aiming for 240RPM, so I increased the amount of microsteps to 800. That made the motor super quiet and will probably bump the torque at full speed (240RPM now) significantly, but maybe not enough to get it past stalling.

- switched to a 12Nm stepper for which I haven't got a torque curve so it's hard to judge what the torque is at 240RPM. I've ran some tests yesterday with very slow ramp ups (PR2 decreased by 1 every 100ms) and the motor was stalling before it got to 240RPM. I've lowered the max speed to 180RPM, it was still stalling, went down to 120RPM and it runs fine. Looking at some videos of the motor in action, I'm judging I can probably push it to 150RPM, but anything higher than that and the torque drops off really quickly.

The acceleration 'ramp' is not linear, as I do this via modifying the PR2 register, the RPM changes vary as the speed goes up ie. the lower the PR2 gets, the higher the speed, but the bigger the impact a 'PR2 - 1' operation has. For example going from PR2 = 155 to 154 means a change in speed from 30.05RPM to 30.24RPM, going from PR2 = 40 to 39 means a change in speed from 114RPM to 117RPM. Not sure if it affects anything, the bigger motor seems to stall at the same spot every single time, but I haven't yet tried a constant RPM delta for ramp up (say 1RPM per 0.025s or similar)

Does switching from 400 microsteps to 800 microsteps decrease torque?

Regards,
T.