Daily Note: Expressive Robotics

These notes are a summary of concepts presented in “Design and Control of a Bipedal Robotic Character.”

Grandia, R., Knoop, E., Hopkins, M. A., Wiedebach, G., Bishop, J., Pickles, S., Müller, D., & Bächer, M. (2024). Design and Control of a Bipedal Robotic Character. Disney Research, Switzerland; Disney Research, USA; Walt Disney Imagineering R&D, USA.

  1. Design Philosophy
    • Emphasis on mechanical simplicity and creative expression
    • Unifying expressive, artist-directed motions with dynamic mobility
    • Focus on character-driven mechanical features and subjective human perception
  2. Control Architecture
    • Reinforcement learning-based system
    • Command signals generated by an animation engine blending multiple animation sources
    • Policies trained for specific motions (walking, standing, animations)
    • Real-time compositing and blending for seamless puppeteering via two-joystick remote control (Steam Deck)
  3. Mechanical Design Principles
    • Creative intent and simplicity prioritized over functional optimization
    • Use of off-the-shelf hardware modules and software-based characterization
    • Rapid prototyping via 3D-printed components
    • Simple, modular design with direct placement of actuators at joints
  4. Motion Generation
    • Procedural gait generation tool for physically plausible walking cycles
    • Model-based optimization to convert animations into feasible trajectories
    • Reinforcement learning for closed-loop control policies imitating reference motions
  5. Puppeteering Interface
    • Combines direct motion control with expressive animations
    • Enables real-time authoring of believable interactions
    • Animation engine synchronizes motions and triggers policy switches
  6. Expressive Features
    • Show functions like LED eyes, head lamps, and speakers synchronized with robot motion
    • Independent neck and head movement (4 DoF)
  7. Robot Specifications
    • Structure
      • 5 DoF per leg; 4 DoF neck and head
        • Rounded soles and urethane foam for dampening impacts
    • Dimensions and weight
      • Height: 0.66 m; Mass: 15.4 kg (torso: 5.8 kg; neck and head: 2.4 kg; legs: 3.6 kg each)
      • Leg lengths: 0.28 m nominal, 0.34 m extended
    • Onboard Systems
      • PC, custom communications board, battery, and IMU
      • Wireless communication via WiFi and LoRa
  8. Performance and Operation
    • Communication rate: 600 Hz
    • Continuous operation for at least 1 hour on a removable battery
    • Integrated actuator drives with with built-in encoders for low-level control