Migrating from TMotorCANControl¶

The APIs are different so a couple of things are needed for a code migration between the two libraries.

Setup¶

TMotorCANControl	cubemarsPyCAN
`TMotorManager_mit_can(motor_type='AK80-9', motor_ID=3)`	`MitMotor(bus, motor_id=3, spec=SPECS["AK80-9"])`
implicit `sudo ip link set can0 up` in the constructor	you bring the interface up; `cubemars doctor` prints the lines
hard-coded `can0` at 1 Mbit/s	any `can.BusABC`, or `CanTransport.open("socketcan:can0")`
process-wide singleton	one `MotorBus` per bus, as many as you like

Control loop¶

# before
with TMotorManager_mit_can(motor_type="AK80-9", motor_ID=3) as dev:
    dev.set_impedance_gains_real_unit(K=10, B=0.5)
    for t in loop:
        dev.update()
        dev.position = 1.0

# after
m = MitMotor(bus, motor_id=3, spec=SPECS["AK80-9"])
with m.control():
    for t in loop:
        state = m.update(position=1.0, kp=10.0, kd=0.5)

update() both sends and returns state, and the state it returns is the snapshot taken at the top of the call — it predates the frame that call sends. The old library’s own demos were inconsistent about this ordering: its MIT demos called update() before setting position, its servo demos after.

Why setpoints are not attributes¶

dev.position = x is gone. MIT packs five coupled fields into one frame, so three assignments produce two intermediate inconsistent commands; a property setter can only clamp silently or raise from an assignment; and m.position reading feedback while m.position = x writes a setpoint means the value you read is never the value you wrote. Servo’s six commands are mutually exclusive, which a kwargs setter cannot express — they are separate types here.

Things that changed because they were wrong¶

Old behaviour	Now
`servo_can.py` raised `NameError` before sending (6 of 7 commands)	works
`set_motor_torque_newton_meters` off by 78× (used `Kt` where it needed the gear ratio)	`output_torque_from_current` / `current_for_output_torque`
servo position scaled by `π/21` — 8.6× wrong	degrees × π/180, and `output_rad` refuses until the gearbox side is measured
`comm_can_set_pos` scaled by 1e6	1e4, per the manual
`set_pos_spd` omitted the `/10` on speed and acceleration	applied
faults raised inside the receive thread, where they vanish	latched, raised on your thread after a safe stop
acceleration sign inverted (`dt = last - now`)	not derived at all; differentiate yourself if you need it
`AK60-6` velocity ±50 rad/s	±45, per the manual
`AK80-64` gear ratio 80	64
fault code 6 labelled “phase current unbalance”	MOSFET over-temperature; code 7 (stall) added
`set_zero_position()` sent origin mode 1 (permanent, writes flash)	`OriginMode.TEMPORARY` by default; permanent refused on single-encoder motors
`Kt` constants marked `UNTESTED CONSTANT!` copied to every motor	per-variant datasheet values, or `UNKNOWN` and the conversion refuses
a `0.59` current fudge factor from one AK80-9 applied everywhere	gone; `estimated_current_a` is explicit and warns
NumPy 2 raised `OverflowError` on any negative servo position	no NumPy dependency at all