Principle:ARISE Initiative Robosuite Mobile Base Velocity Control
| Knowledge Sources | |
|---|---|
| Domains | Robotics, Mobile Robotics, Control Theory |
| Last Updated | 2026-02-15 07:00 GMT |
Overview
Mobile base velocity control converts planar velocity commands into actuator signals for wheeled or legged robot bases, handling coordinate frame transformations between the policy's reference frame and the base's current heading.
Description
Mobile manipulation robots combine a navigating base with one or more manipulator arms. The mobile base controller handles the locomotion component, accepting velocity commands (typically forward velocity, lateral velocity, and rotational velocity) and converting them into actuator signals that drive the base. Unlike arm controllers that output joint torques, mobile base velocity controllers typically output scaled velocity commands that map directly to the simulator's velocity-controlled actuators.
A central challenge in mobile base control is the coordinate frame transformation. Policies typically issue velocity commands relative to the robot's current heading (body frame), but the simulator's actuators operate in a fixed world frame. The controller must transform the policy's body-frame velocity commands into the world frame, accounting for the base's current orientation relative to its initial orientation at the start of the episode. This involves a 2D rotation of the translational velocity components by the yaw angle difference between the current and initial base orientations.
The controller reads the base pose from a designated reference site in the simulator, extracts the yaw angle from the orientation matrix, and applies the inverse rotation to map policy commands from the current body frame back to the initial frame. The transformed velocities are then linearly mapped from the normalized action range to the actuator control range using bias and weight terms computed from the actuator limits.
Usage
Apply mobile base velocity control when a robot has a navigating base (wheeled, omnidirectional, or legged) that must respond to velocity-level navigation commands. This is the standard control mode for mobile manipulation tasks where the policy outputs a combination of base velocity commands and arm action commands. The coordinate frame transformation is essential for consistent behavior regardless of the base's accumulated heading change during an episode.
Theoretical Basis
Mobile Base Velocity Control:
Given:
- Policy action: [v_x, v_y, omega] in current body frame
- Initial base orientation: R_init (rotation matrix at episode start)
- Current base orientation: R_curr (current rotation matrix)
- Actuator range: [ctrl_min, ctrl_max]
1. Extract yaw angles:
theta_init = yaw(R_init)
theta_curr = yaw(R_curr)
delta_theta = theta_curr - theta_init
2. Transform velocity from current body frame to initial frame:
v_x' = v_x * cos(delta_theta) + v_y * sin(delta_theta)
v_y' = -v_x * sin(delta_theta) + v_y * cos(delta_theta)
omega' = omega (rotation is frame-invariant for yaw)
3. Scale to actuator range:
bias = 0.5 * (ctrl_max + ctrl_min)
weight = 0.5 * (ctrl_max - ctrl_min)
output = bias + weight * [v_x', v_y', omega']
4. Return output as actuator commands
Key design decisions:
- Body-to-initial frame transformation: Rotating commands by the accumulated yaw difference ensures the policy's "forward" always corresponds to the robot's initial forward direction, providing consistency across the episode.
- Velocity-level actuation: Unlike arm controllers that produce torques, mobile base controllers output velocity-scaled actuator commands, reflecting the velocity-controlled nature of most wheeled base actuators.
- Separate base controller hierarchy: The mobile base controller has its own base class, distinct from the arm controller base class, because mobile bases lack end-effector references, Jacobians, and mass matrices.
- Legacy compatibility: A backward-compatible variant handles changes in the forward-axis convention of the base model by dynamically detecting the joint axis and reordering actions accordingly.