Actuators

Actuators are parts fitted into slots, exactly like the sensors. The concepts live in Slots and assembly, the vehicle’s slots and their accepted types in the configuration page, and new parts can be added following the Add a part guide.

Available actuators

Actuator	Part	Slot	Fitted by default
M200 weedless propellers	`m200_weedless_prop_ccw` / `_cw`	`motor_port`, `motor_stbd`	yes
T200 propellers	`t200_prop_ccw` / `_cw`	`motor_port`, `motor_stbd`	no

Actuators ROS API

Thrusters

Each thruster plugin subscribes to a gz transport topic. Each of those gz topics is bridged to ROS and named after its motor, under the instance name, <name>: blueboat for the default instance, which the commands below use, or whatever the boat was spawned as (Several vehicles).

ROS Topic	Description	Message type
`/<name>/motor_port/cmd`	Normalized thrust command in [-1, 1]: +1 full ahead, -1 full astern, 0 stop	std_msgs/msg/Float64
`/<name>/motor_stbd/cmd`	Normalized thrust command in [-1, 1]: +1 full ahead, -1 full astern, 0 stop	std_msgs/msg/Float64

The command is a fraction of the propeller’s own limits, which the model takes from the part’s drive table - 51.5 N ahead and -40.2 N astern for a T200 at 16 V. The two directions scale independently, so +0.5 and -0.5 are equal command and unequal force. Values outside [-1, 1] are clamped.

Equal command drives ahead; differential command yaws (more starboard turns to port and vice versa). To manually send thruster commands via ROS:

ros2 topic pub /blueboat/motor_port/cmd std_msgs/msg/Float64 "data: 0.4" -1 &
ros2 topic pub /blueboat/motor_stbd/cmd std_msgs/msg/Float64 "data: 0.4" -1 &
wait

Command both motors together

Commands latch: each motor holds its last command until a new one arrives, and bringing the motors up one command at a time applies a differential wrench while the second command is in flight, yawing the boat off its heading. The & + wait above publishes in parallel; controllers that publish continuously are unaffected. Stop with data: 0.0 to both.

To drive with a gamepad instead, a ready mixer for either vehicle is in Teleoperate with a gamepad.

Gazebo transport API

The same topics exist on the Gazebo side (the bridge exposes them to ROS under the same names), plus a speed feedback per motor:

gz Topic	Description	Message type
`/<name>/motor_<side>/cmd`	Normalized thrust command in [-1, 1]	`gz.msgs.Double`
`/<name>/motor_<side>/cmd/ang_vel`	Propeller speed feedback (rad/s)	`gz.msgs.Double`

gz topic -t /blueboat/motor_port/cmd -m gz.msgs.Double -p 'data: 0.2' &
gz topic -t /blueboat/motor_stbd/cmd -m gz.msgs.Double -p 'data: 0.2' &
wait

A command topic follows the part’s own name: fit a different propeller, rename it or leave a motor slot empty and the topics follow the fitted parts (Configuration).