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sancho_control

The sancho_control package provides hardware-agnostic control logic for the Sancho robot. It houses the head tracking system, which converts 2D pixel positions of detected faces into pan/tilt servo commands to keep users centered in the camera's field of view.

Nodes

head_control_face_tracker (Lifecycle)

Visually tracks a target face using an Exponential Moving Average (EMA) pixel filter for smoothing. Computes angular error from the camera center using intrinsic calibrations, and applies a Proportional (P) controller to generate pan/tilt goals for the head servos.

ROS 2 API

Subscribed Topics

Topic Type Description
/sancho_perception/human_tracking sancho_interfaces/msg/FaceDetectionArray Detected faces in camera frame
/sancho_camera/camera_info sensor_msgs/msg/CameraInfo Focal lengths and optical center for angular error computation
/wxxms/joint_states sensor_msgs/msg/JointState Current head servo positions

Published Topics

Topic Type Description
/head_goal geometry_msgs/msg/PoseStamped Desired pan/tilt angles encoded in quaternion orientation

Parameters

Parameter Type Default Description
face_topic string "/sancho_perception/human_tracking" Input face detection topic
head_goal_topic string "/head_goal" Output head goal topic
camera_frame string "camera_frame" Frame ID in target message
control_rate double 10.0 Control loop frequency (Hz)
ema_alpha double 0.2 EMA smoothing factor (lower = smoother)
p_gain_pan double 0.8 Proportional gain for horizontal tracking
p_gain_tilt double 0.8 Proportional gain for vertical tracking
timeout_no_detection double 1.0 Seconds before abandoning track
pan_joint string "pan" Pan servo name in joint_states
tilt_joint string "tilt" Tilt servo name in joint_states

Lifecycle Information

Transition Behavior
on_configure Resolves parameters, creates publisher for /head_goal
on_activate Subscribes to camera, face, and joint state topics; starts control loop timer
on_deactivate Destroys timers and subscriptions, halts head commands

Dependencies

  • Internal: sancho_interfaces
  • External: rclpy, geometry_msgs, sensor_msgs, std_msgs, lifecycle_msgs, tf_transformations