Commander

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Version: [ , 2026.08 , 2026.04 ]

The commander port is used to send control set-points for the roll/pitch/yaw/thrust regulators from the host to the Crazyflie. As soon as the communication link has been established these packets can be sent and the values are valid until the next packet is received. The packets are decoded in src/modules/src/crtp_commander_rpyt.c.

Communication protocol

        +-------+-------+-------+-------+
        | ROLL  | PITCH |  YAW  |THRUST |
        +-------+-------+-------+-------+
Length      4       4       4       2      bytes
Name Byte Size Type Comment
ROLL 0-3 4 float Roll set-point, degrees (angle mode) or degrees/s (rate mode)
PITCH 4-7 4 float Pitch set-point, degrees (angle mode) or degrees/s (rate mode)
YAW 8-11 4 float Yaw set-point, degrees/s (rate mode, default) or degrees (angle mode)
THRUST 12-13 2 uint16_t Thrust set-point, 0 - 65535

In rate mode the yaw value is negated on reception, so a positive value rotates the Crazyflie clockwise seen from above.

Thrust

The thrust field is passed to the controller as a 16 bit value. With CONFIG_ENABLE_THRUST_BAT_COMPENSATED enabled it is linear in force: a motor commanded with value t produces t / UINT16_MAX * THRUST_MAX newtons (see platform_defaults_cf2.h), independent of battery voltage. Without battery compensation the value is used directly as PWM duty cycle, which is not linear in thrust and dependent on battery voltage.

  • Thrust lock. After connecting, and whenever the commander priority is disabled, non-zero thrust is ignored until a packet with thrust 0 has been received. This prevents the motors from starting on a stale or unintended set-point.
  • Lower bound. Thrust values below MIN_THRUST are treated as zero. If CONFIG_ENABLE_THRUST_BAT_COMPENSATED is enabled (default), the limit is computed by THRUST_MIN / THRUST_MAX * UINT16_MAX.
  • Upper bound. There is no clipping in the commander. The per-motor output is capped to the PWM range in the power distribution.

Flight modes

The flightmode parameter group changes how the four fields are interpreted.

Parameter Effect
stabModeRoll, stabModePitch, stabModeYaw 0: rate control, 1: angle control. Defaults are angle for roll/pitch and rate for yaw.
althold Thrust becomes a vertical velocity set-point centred at 32767; roll/pitch/yaw unchanged.
poshold Roll and pitch become Y and X velocity set-points (value / 30 m/s); thrust as above.
posSet Roll, pitch and thrust become absolute Y, X (m) and Z (thrust / 1000 m) positions, yaw becomes an absolute angle.
yawMode Frame used for roll/pitch in yaw rate mode: 1 plus-mode, 2 x-mode (default).

Example

ramp.py: Sends low-level roll/pitch/yaw/thrust set-points directly using the Commander class, ramping thrust up and down.

Set-points must be sent continuously, see the watchdog timeouts in the commander framework.