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STEPFOC and Spectral Micro

STEPFOC and the Spectral Micro BLDC driver are sister drivers: similar hardware and similar firmware, each made for its kind of motor. The Spectral Micro drives three-phase brushless motors; STEPFOC drives two-phase stepper motors.

They are not the same board and do not run the same firmware, but they are controlled and run practically the same way: the same CAN and UART commands, the same Python library, Motor GUI and bootloader.

What this means in practice:

  • The commands are practically the same. The CAN messages and UART commands of the Reference have the same IDs, names and layouts on both drivers; STEPFOC adds a few that only make sense on a stepper (homing against a sensor, open-loop stepping). A program written for one runs on the other.
  • The firmware releases go in step, and from 109 share their numbers. A change that applies to both drivers comes to both. From release 109 they are released together under the same version number; the Spectral Micro went from 107 straight to 109, so there is no Spectral Micro 108. Before, the numbers did not always match (STEPFOC 108 went with Spectral Micro 107); the compatibility table lists the pairs.
  • Calibration differs. A BLDC driver measures the motor's resistance and inductance and finds its pole pairs; STEPFOC cannot, so you enter the three values from the motor's datasheet before calibrating. See Motor parameters and calibration. From firmware 109 #Cal is followed by the encoder table and the anti-cogging on both drivers.
  • Some defaults differ. Each driver's were measured on its own bench: the direct PLL speed estimate at 60 Hz and 166 µs delay compensation here, 100 Hz and 234 µs on the Spectral Micro; velocity gains 0.02 / 0.001 here, 0.03 / 0.0003 there. STEPFOC brakes in idle by default, the Spectral Micro coasts.
  • The motor terminals differ. A+, A−, B+, B− for the two stepper coils instead of U, V, W.
  • Some images on this site show a Spectral Micro. Where a photo or a screenshot shows the BLDC board, the procedure is the same for STEPFOC.

The guides under the Guides tab were written with the Spectral Micro; the code in them runs unchanged on STEPFOC.

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