# 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. ```mermaid 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](https://docs.source-robotics.com/STEPFOC-docs/108/06-operation/errors/). | 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](#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](#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. !!! warning "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

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

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](https://docs.source-robotics.com/STEPFOC-docs/108/03-technical-data/ratings/)), 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. !!! warning "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 ![Positive rotation is counter-clockwise looking at the encoder magnet. A positive current turns the motor that way, a positive speed too, and the position grows.](https://docs.source-robotics.com/STEPFOC-docs/108/assets/STEPFOC_ORIENTATION.webp){ width="700" } ## 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.