Robot ROS Interface

What RealRobotBackend exchanges with the robot, for anyone who debugs pib3 or talks to the robot without it. Everything goes through rosbridge, the robot's WebSocket bridge to ROS 2: ws://<robot-ip>:9090. The names and types below are those of pib-backend's b3 fork (mamrehn/pib-backend, branch develop).

Service types work in the short form (datatypes/ApplyJointTrajectory) and the long form (datatypes/srv/ApplyJointTrajectory); rosbridge resolves both.

Joints

Name	Kind	Type	pib3 uses it for
/apply_joint_trajectory	service	datatypes/srv/ApplyJointTrajectory	moving joints in motor_mode="ros"
/joint_trajectory	topic, robot → client	trajectory_msgs/msg/JointTrajectory	joint positions (get_joint)
/get_joint_position	service	datatypes/srv/GetJointPosition	not used
/motor_settings	topic, robot → client	datatypes/msg/MotorSettings	the settings cache
/apply_motor_settings	service	datatypes/srv/ApplyMotorSettings	changing motor settings
/motor_current	topic, robot → client	diagnostic_msgs/msg/DiagnosticStatus	not used

Units

Positions are centidegrees (1/100 degree): 9000 is 90°, -4500 is −45°. pib3 converts from radians or percent before it sends anything; see Unit Conventions.

Moving joints

/apply_joint_trajectory takes a trajectory_msgs/JointTrajectory and answers bool successful. The robot reads the message in one of two layouts:

1. One point per joint (what pib3 sends): joint_names[i] goes to points[i].positions[0], and every time_from_start is zero. Each motor moves to its target at its own configured speed (/motor_settings); the message's velocities are ignored.
2. Timed trajectory: any point with a non-zero time_from_start, or several waypoints that each carry a position per joint. The robot interpolates every joint smoothly through the waypoints at 100 Hz.

One point with several positions moves one joint

A single point that carries all positions, with time_from_start zero, is read as layout 1: only the first joint moves, and the others are dropped without an error. joint_trajectory_message() in pib3/backends/robot.py builds layout 1 for this reason.

from pib3.backends.robot import joint_trajectory_message

# Head turn to 45°, right elbow to 90°, in one request (layout 1)
request = joint_trajectory_message(
    ["turn_head_motor", "elbow_right"], [4500, 9000]
)

Reading positions

The robot publishes one /joint_trajectory message per motor after each command it applied: joint_names holds the motor's name and points[0].positions[0] its position in centidegrees. Publishing to /joint_trajectory yourself moves nothing; only /apply_joint_trajectory moves motors. /get_joint_position (string joint_name → bool successful, int32 position, string message) asks for one motor on demand.

Motor current

/motor_current carries one DiagnosticStatus per motor and reading: name is the motor, values[0].value its current in mA as a string, and level turns WARN from 1500 mA. The robot publishes it once per second and whenever the servo bricklet reports a change.

Motor settings

/apply_motor_settings takes a MotorSettings and answers bool settings_applied and bool settings_persisted. The fields: motor_name, turned_on, pulse_width_min, pulse_width_max, rotation_range_min, rotation_range_max (centidegrees), velocity, acceleration, deceleration (centidegrees per second, per second²), period, visible and invert. The robot publishes the result on /motor_settings.

Motor names

The 26 motors match pib3.Joint; the two all_fingers_* names move every finger motor of one hand at once.

Group	Motor names
Head	turn_head_motor, tilt_forward_motor
Left arm	shoulder_vertical_left, shoulder_horizontal_left, upper_arm_left_rotation, elbow_left, lower_arm_left_rotation, wrist_left
Left hand	thumb_left_opposition, thumb_left_stretch, index_left_stretch, middle_left_stretch, ring_left_stretch, pinky_left_stretch, all_fingers_left
Right arm	shoulder_vertical_right, shoulder_horizontal_right, upper_arm_right_rotation, elbow_right, lower_arm_right_rotation, wrist_right
Right hand	thumb_right_opposition, thumb_right_stretch, index_right_stretch, middle_right_stretch, ring_right_stretch, pinky_right_stretch, all_fingers_right

Audio

Audio topics and services are described in the Audio System reference.

Camera and AI models

The model services (/list_models, /start_model, /stop_model, /get_detections) and the detections/<model_id> topics are described in AI & Camera Subsystems.

Service calls that take longer than 5 s

rosbridge abandons a service call after 5 s unless the call_service message names a timeout. roslibpy never sends one, so pib3 builds the message itself for /start_model and /stop_model, where the camera answers only after rebuilding its pipeline.