I've seen all the incredible work you've put on this project and I'm willing to first thank you for documenting it thoroughly.
However for my application I need speed and looking at your video portions where it was running at 100% it seems way too slow for my needs.
Then I went on documenting my self about the big industrial robot and I've realized that stepper motor are used only for the grip of certain robot "hand" (soft robotic is much better though), but for main axis movement they use brushless motor + encoders. This video seems to confirm my finding
This is 1o1(+1) comparison testing
Interesting enough ODrive can also be driven in step mode.
It seems like an ESC with some nice interface/api (in python) to control it and UART/SPI/1wire comunication.
Quite expensive it though... €119.00 to control 2 motor so 357€ for 6 DOF + encoders + motors
but I can avoid arduino entirelly and control it with the rasberry.
So my plan is to buy all the hardware stuff for AR2 and apply it for brushless.