Feedforward speed control with shared battery compensation - #118
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Feedforward speed control with shared battery compensation#118SaintSampo wants to merge 4 commits into
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Centralize and clarify encoder timing and unit conversions. In encoded_motor.py introduce _UPDATE_PERIOD_MS/_UPDATE_HZ, conversion helpers (_counts_per_update_to_rpm, _rpm_to_counts_per_update), and store counts-per-update instead of ambiguous `speed`. Use the update period constant for the virtual timer and for rpm<->counts conversions. Update set_speed/get_speed/inner update logic to use the new helpers and names. In differential_drive.py rename cmpsToRPM to snake_case cmps_to_rpm for naming consistency. Improves readability and correctness of rpm/count calculations.
Move battery voltage measurement/compensation onto Board (nominal voltage per platform, update_voltage_compensation(), voltage_scale measured at init). DifferentialDrive now reads board.voltage_scale (removed its own redundant voltage logic). EncodedMotor switched to feedforward+P velocity control (kS/kV per platform), holds Board reference, applies voltage_scale to motor effort, and clamps effort to [-1,1]. Minor PID/integral changes to match the new feedforward approach.
Update EncodedMotor defaults: NanoXRP now uses zeroed feedforward (kS/kV = 0.00) with a P-only PID (kp=0.015). Other platforms use kS=0.12, kV=0.02 and a stronger P-only PID (kp=0.1). Also clear prev_speed (set to 0) when stopping so direction is forgotten when the controller is cleared.
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Summary
Reworks the motor speed loop from a pure PI controller into feedforward + P with battery compensation, and cleans up the speed math along the way. Feedforward (kS to break stiction, kV per unit speed) does the bulk of the work.
Changes
Speed control law (
encoded_motor.py)kS·sign(target) + kV·target + kP·error, scaled by batteryvoltage_scale. Integral dropped (with feedforward carrying the load, the residual is small and voltage comp absorbs droop).kS/kVare per-motor attributes;kPis the injectable controller'skp(set_speed_controllerstill works).kS=0.12, kV=0.02, kp=0.1; NanokS=0.1, kV=0.00122, kpsmall (Nano's high gear ratio/resolution makes the P loop go unstable above ~0.03).Battery compensation centralized on Board (
board.py)voltage_scale+update_voltage_compensation()now live onBoard, measured once at construction and shared by every consumer. Removes the duplicate copies the drivetrain and motors each held.Speed-math cleanup (
encoded_motor.py,differential_drive.py)_UPDATE_PERIOD_MS/_UPDATE_HZconstants replace the magicperiod=20/60*50that had to agree by hand._rpm_to_counts_per_update/_counts_per_update_to_rpmhold the conversion in one place (get_speed/set_speedcall them).self.speed(counts-per-tick) toself._counts_per_update.set_speed(0/None)now resetsprev_speedso the direction-change reset can't key off a stale value.API notes
DifferentialDrive.update_voltage_compensation()removed — callBoard.get_default_board().update_voltage_compensation()instead (e.g. after a battery swap).Boardnow measures the battery once at construction (one 8-sample read); on the Nano this leaves the shared VIN/RM2 pin restored to output, which is friendlier to BLE than before.