Control modes¶

The driver is always in one control mode. A command that carries a setpoint switches to the mode that uses it; #Idle or Send_Idle switches back to idle. The driver refuses every mode except idle, open loop included, while it is not calibrated or while an error is active.

stateDiagram-v2
    [*] --> NotCalibrated: power-up, no saved calibration
    [*] --> Idle: power-up, saved calibration
    NotCalibrated --> Calibration: #Cal
    Calibration --> Idle: success, #Save
    Calibration --> NotCalibrated: a test fails
    Idle --> ControlMode: a setpoint
    ControlMode --> Idle: #Idle, Send_Idle
    ControlMode --> Error: a fault
    Idle --> Error: a fault
    Error --> Idle: #Clear, cause gone

A setpoint is #P, #V, #Iq, #PD or a CAN motion frame, and a new setpoint switches the mode without passing through idle; a fault is any of the errors on Errors and recovery.

ControlMode	What the motor does	Entered by	Setpoint unit
Idle	nothing: brakes (phases shorted), the default, or coasts (phases open), as set by `#Brake` / `#Coast` or Send_Settings; see Braking in idle	`#Idle`, Send_Idle, `#Clear`, errors	—
Position	holds and moves to a position with the cascade of position, velocity and current loops	`#P`, Send_data_pack_1 (8 bytes)	encoder ticks
Velocity	turns at a speed with the velocity and current loops	`#V`, Send_data_pack_1 (5 bytes)	encoder ticks/s
Current (torque)	applies a current, so a torque, with the current loop alone	`#Iq`, Send_data_pack_1 (2 bytes)	mA
PD (impedance)	behaves like a spring and a damper around a position, with `KP` and `KD`	`#PD`, Send_data_pack_PD	encoder ticks
Voltage torque	applies a voltage on the q axis directly, without the current loop: clamped to `#Vlim`, not current-limited	`#Uq`	mV
Open loop	steps the motor like a plain stepper driver, without the encoder and without a current limit; see Open-loop stepping	`#Openloop` (continuous), `#gosteps` (a number of microsteps)	electrical rad/s; microsteps
HALL	spins until a sensor on ADDITIONAL2 triggers, then holds the position reached; with a level trigger only while the pin stays at that level	`#HALL`, Send_data_pack_HALL	encoder ticks/s
Gripper	runs the gripper state machine: move to a jaw position with a speed and a current limit	`#Grippos`, Send_gripper_data_pack (with `#Gripper 1`)	0 to 255
Calibration	the calibration routine, and the angle-offset step alone	`#Cal`, `#Calangle`, `#Gripcal`	—

Braking in idle¶

In idle the driver brakes: it keeps both coils shorted through the driver stage, so the motor resists being turned. It does so at every power-up, and also with an error, which puts the driver in idle. #Coast (or Send_Settings over CAN) lets the motor coast instead, with the coils open, until the next power-up: #Save does not keep it. #Brake brakes again.

The braking current is not limited

A motor that is turned while it brakes drives its own back-EMF current through the shorted coils, and the current loop does not limit that current. Do not let a load drive a braking motor fast; send #Coast first when the shaft must turn freely.

Units¶

Position is in encoder ticks: 16384 per revolution of the motor shaft, counting up without limit over several revolutions. Positive is counter-clockwise seen from the magnet (the back of the motor).
Speed is in encoder ticks per second: 16384 is one revolution per second, 60 rpm.
Current is in mA. Torque is current times the motor's Kt, which calibration finds.
Feedforward: the 8-byte motion frame carries a speed and a current feedforward beside the position, the 5-byte one a current feedforward beside the speed. They are added after the loops, so a host that knows the trajectory can command it directly and leave the loops to correct the rest. Send 0 when you do not use them.

Try it¶

Ticks (a position, or a speed per second) Pole pairs

As a position: 1.000 turns, 360.0° · as a speed: 60 rpm · the practical maximum for 50 pole pairs is about 720 rpm

Kt in Nm/A (what #Kt prints) Current in mA

Torque: 0.21 Nm, 21 N·cm

The units of this page, with your numbers: 16384 encoder ticks per turn, the practical speed limit from the electrical frequency the control loop can follow (Ratings and limits), and the torque as Kt times the current.

Open-loop stepping¶

#Openloop and #gosteps drive the coils like a plain stepper driver, without the encoder in the loop. Like every other mode, they need a calibrated driver without errors.

#Openloop 50 turns the field at 50 electrical rad/s and keeps turning until another command. On a motor with 50 pole pairs that is 50 ÷ (2π × 50), about 0.16 revolutions per second.
#gosteps 64 makes 64 microsteps, then goes to idle; a negative number goes the other way. #microstep (16 by default) is the number of microsteps per electrical cycle, which is four full steps: with 16, #gosteps 16 turns a 1.8° motor by 7.2°. #stepinterval (1000 µs by default) is the time between two microsteps, rounded down to whole control cycles of 160 µs.
#Openv (5000 mV by default) is the voltage both put on the coils.

None of these settings is saved.

Open loop is not current-limited

Open loop applies a voltage, not a current, and #Ilim does not apply. At standstill and low speed the coil current is about #Openv ÷ R: the default 5000 mV drives about 4.5 A through a 1.1 Ω coil, more than the driver's 2.8 A and the motor's rating. Set #Openv to the rated current × R first (2 A × 1.1 Ω = 2200 mV), and keep the test short.

Positive rotation¶

Which mode am I in?¶

#Mode prints the mode: Idle mode, Position control, Speed control, Current control, PD control, Open loop, Gripper mode or Gripper calib mode. In this firmware release the voltage-torque mode reads Gripper mode too (a leftover label), and HALL mode, the angle-offset search (#Calangle), open-loop steps (#gosteps) and gripper mode print nothing. The behaviour of the motor is the reliable check there.

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