Matt Hein did a couple of blog posts about using BEMF as a load sensing tool, but they were never completed.
In my own testing, I've seen some traces that make me think it's possible. Attached is a .gif of a pair of traces. The sine is the current in phase 1A, the green is the BEMF pin, measured across the required capacitor, right on the BOOST-DRV8711 board (yes, I know it looks ugly).
24V Vm
2.1A 1.8d motor
4,8mH/phase
1.8R/phase
NEMA23 frame.
Loaded:
Unloaded:
Has anyone successfully used BEMF to track stepper load? I know that BEMF tracks mainly with RPM, and load is a minor component, but it seems like something that Trinamic and others are using to some effect.
My thought is that the large differences that center around the bottom half of the drive sine could be used as a per-cycle indicator of load. Yes, it's specific to my motor and my mechanical arrangement, but in general, I think this may have applications beyond my simple constant-speed drive.