Hi Ben,
I measured the coil current with the DRV8825 in full-step mode and the pulse input tied HIGH (3.3V). No, the motor was not stepping when the current was measured. I’m using a 12V/4A supply for drive power with a 50V/100uF electrolytic capacitor installed across the power input terminals. The original measured current was approx. 250ma and I believe the Vref was set to approx. 0.35V but unfortunately I did not re-measure it before I made changes (you can take a look here for more info on the setting of the 0.35V value … https://forum.pololu.com/t/setting-current-limit-on-drv8825-md20a-with-1206-stepper/5725/1). Based on this setup, I re-adjusted the pot to provide approx. 640ma of current and this is what I used for the testing data I provided above (using 1/16 micro-step mode). I’m assuming this setup is now correct, yes?
Thanks for the details on the micro-step current settings. Yes, that makes sense.
I figured the heat would vary in proportion with the current based on I[size=85]2[/size]R but didn’t really originally get the fact that the heat is reduced at higher step rates. I can now see more diminished current readings when I step more quickly, so it would make sense that it should run cooler at higher step frequencies. However, in my case, running the same code that I had with the original pot setting and again with the new pot setting (i.e. same move profile) results in a cooler running motor with the new settings.
Regarding ramp-up profile & timing, should I be looking for better results than what I’m showing? With what I have, I’m able to get the unloaded motor to ramp-up to 45.3K step frequency (using a 11us interrupt firing) and run consistently within 40ms. Should I be able to do better than this? Yes, I’ll play around with making a more consistent step frequency delta during the ramp-up. However, I found that if I made less radical frequency changes as I got closer to the target value, I was able to support a slightly higher final step frequency. One issue I’ll have later is that I really need to attain the ramp-up as quickly as I can since I’ll be moving to discrete points and not just spinning the motor constantly. The max. step frequency I’ll apply for a given move will be based on the parameters of the move (i.e. faster speeds for longer moves & different ramp-ups based on the move distance).
I’ll continue working through this and will post back when I have more info to share. Please let me know if you have any comments on any of this. Appreciate your help.