Glossary¶

Activated: A flag the driver keeps (#Activate, Send_gripper_data_pack). In gripper mode a move is carried out only while the gripper is activated.
ADDITIONAL2: A spare pin of the driver, usable as an analog input or a digital input/output. HALL mode homes the motor against a sensor wired to it.
Angle offset (theta offset): The angle between the encoder's zero and the motor's electrical zero, found by calibration and stored. The driver needs it to place the current vector relative to the rotor.
Back-EMF: The voltage a turning motor generates in its own coils, proportional to speed. It opposes the supply, limits the top speed at a given voltage. Calibration estimates KV from the speed the motor reaches per volt.
Board ID: The bootloader's own address, 0 to 13, stored in its configuration page. Saving the configuration (#Save) writes the CAN node ID into it.
Bootloader: The program in the first 12 KB of the driver's flash on boards shipped with firmware 105 or newer, and on some shipped before. It starts the firmware, and loads a new firmware over UART or CAN. See The bootloader.
Calibration: The routine (#Cal) that checks the magnet and the supply, takes the motor's resistance, inductance and pole pairs, computes the current loop gains, spins the motor in open loop to learn the wiring, finds the angle offset and measures Kt, KV and the flux linkage. Its result is kept with #Save.
CAN ID (node ID): The address of the driver on the CAN bus, 0 to 13 (the bootloader reserves 14 and 15). It occupies bits 10 to 7 of the 11-bit CAN frame identifier; the command ID occupies bits 6 to 1 and the error bit is bit 0.
CANvas: Source Robotics' USB-to-CAN adapter. It appears as a serial port and speaks slcan, which python-can and Motor GUI use.
Command ID: The number, 0 to 63, in bits 6 to 1 of a CAN frame identifier that says which message the frame carries. The API reference lists every command ID.
Commutation: Placing the stator current so that it produces torque at the rotor's present angle. FOC does it continuously from the encoder angle and the angle offset; a conventional stepper driver does it blindly, step by step.
Control mode: What the driver is doing with the motor: idle, position, velocity, current, PD (impedance), voltage torque, open loop, HALL, gripper, or calibration. A command that carries a setpoint puts the driver in the matching mode.
Current loop bandwidth (#Cbw): How fast the current loop follows a change of its setpoint, in Hz. Calibration computes the current loop gains from it and the motor's resistance and inductance; 500 Hz by default.
Daisy chain: Several drivers on one CAN bus and one supply, each driver's second CAN and power connector feeding the next.
d-q frame: The rotating frame of reference FOC works in: the q axis is at right angles to the rotor field and the current on it (Iq) produces torque; the d axis is along the field and its current (Id) produces none, so it is held at 0.
Diametrical magnet: A disc magnet whose poles are across its diameter, so the field turns with the shaft. The encoder needs this kind; an axially magnetised disc looks the same and does not work.
EEPROM: The non-volatile memory on the driver that holds the configuration and the calibration. #Save writes it, #Default restores the factory values.
Encoder ticks: The unit of position: the 14-bit magnetic encoder gives 16384 ticks per revolution of the motor shaft, counted over as many revolutions as the motor makes. Speed is in ticks per second.
Error bit: Bit 0 of every CAN frame identifier the driver sends: 1 while any error is active.
Feedforward: A term added to a loop's output from what is known in advance rather than from the error: the motion frames carry a speed and a current feedforward so a host that knows the trajectory can command it directly, leaving the loops to correct the rest.
Field-oriented control (FOC): Controlling a motor by regulating the stator current as a vector in the rotor's frame, from a measurement of the rotor angle. On a stepper it replaces the fixed step currents with sinusoidal currents that follow the rotor, which gives smooth, quiet, efficient motion with no lost steps and a known position.
Firmware release: One build of the firmware, numbered 103, 105, 106, … and tagged V103, V105, … in the firmware repository. #Info prints the release a driver runs. This documentation describes one release; the version selector switches between them.
Flux linkage: The rotor's magnetic flux as seen by a coil, in weber; calibration computes it from Kt.
Gripper mode: The driver running a gripper (#Gripper 1): jaw positions from 0 (open) to 255 (closed), a speed, a current limit that becomes the grip force, and object detection.
HALL mode: Homing against a sensor on ADDITIONAL2: the motor turns at a set speed until the sensor triggers, then holds the position reached. With a level trigger it holds only while the pin stays at that level.
Heartbeat: A frame (Respond_Heartbeat) the driver sends at a set interval so the host knows it is alive. Off by default.
Iq, Id: The two components of the motor current in the d-q frame: Iq produces torque, Id is normally held at 0. The current mode's setpoint and limit are Iq values.
Impedance (PD) mode: The control mode in which the driver behaves like a spring and a damper around a position setpoint, with the stiffness KP and the damping KD, plus a current feedforward.
Kt, KV: The motor's torque constant (torque per ampere) and velocity constant (speed per volt), found by calibration. Kt turns a current into an estimated torque; KV gives the top speed at a supply voltage.
Microstepping: Driving a stepper with intermediate current levels between full steps. Only the open-loop commands (#gosteps, #microstep) use it; under FOC the current follows the rotor continuously.
Motor GUI: Source Robotics' browser tool for the driver: tuning, plots and firmware updates over a serial or CAN adapter.
Open loop: Driving the motor as a plain stepper, without the encoder in the loop: #Openloop, #gosteps, and the open-loop spin of the calibration.
Phase order: How the stepper's two coils are connected to A+/A− and B+/B−. Firmware 105 and newer learns the wiring during calibration and compensates it; firmware 103 asks for the wires to be swapped when it is reversed.
Pole pairs: The number of electrical cycles per mechanical revolution: 50 for a 1.8° stepper, 100 for a 0.9° stepper. Set with #PP before calibration.
Remote frame: A CAN frame with the RTR bit set and no data: a request. The host asks for data with a remote frame under a command ID, and the driver answers with a data frame under the same ID.
Spectral Micro: Source Robotics' BLDC driver, STEPFOC's sister: similar hardware and firmware and practically the same commands, for three-phase brushless motors.
Step angle: The angle of one full step of a stepper: 1.8° for the common 200-step motor, 0.9° for a 400-step motor. It sets the pole pairs: 360 ÷ (4 × step angle).
Termination: The 120 Ω resistor the first and the last node of a CAN bus need. The switch on the driver turns it on.
Vbus: The supply voltage at the driver, measured and printed in mV. Outside the limits the driver raises a Vbus error.
Watchdog: A timer the driver resets with every motion frame and every status request it answers. When it is set (Send_Watchdog) and runs out, the driver reports a watchdog error and stops.

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