Ernest Wang

Wheel-legged Robot

Project Overview

This robot was built with one goal in mind - mobility in unstructured environments. Key Principles:

  • Stability: constantly balancing on its own
  • Low Complexity: few moving parts
  • Energy Efficiency

Leg Design

The leg mechanism is a four-bar linkage driven by a single actuator at the hip. It’s designed for vertical compliance, stability and geometric simplicity.

Core Components:

  • Hip Motor: The only actuator. All movements is derived from it. With position feedback.
  • Thigh Rod: Connects the actuator to the mechanism
  • Drive Rod: Maintains platform orientation through parallel linkage. Mechanically decouples body pitch from leg motion
  • Calf rod: interacts with the ground, integrates the wheel and passive compliance. This structure ensures that the platform stays horizontal regardless of leg movement. |200****|500

Control System

The robot uses a two-loop architecture to separate body control from leg motion:

Body Stabilization - LQR

LQR logic is broken down into multiple PID controllers:

  1. Angle feedback: Stabilizes Pitch using MPU6050 angle (Y-axis)
  2. Gyro feedback: Dampens oscillations with angular velocity
  3. Displacement: Uses AS5600 encoders to maintain position
  4. Velocity: Regulates forward/backward motion Instead of solving Riccati equations, the LQR weights are manually tuned as 4 PID terms.
Yaw Control
  • Integrates IMU yaw angle using angular unwrapping
  • PID control on yaw angle and gyro for smooth heading correction
  • Yaw correction applied symmetrically to wheel torque
Fall Detection & Recovery
  • if pitch exceeds , disables motor torque
  • automatically resumes balancing after recovery timeout

Leg Control & Jumping

Roll-Stabilized Leg Height Control
  • Uses roll axis from IMU to stabilize lateral motion.
  • Applies filtered PID correction to servo targets.
  • Leg position scaled based on joystick-controlled body height
Jump Mechanism
  • Rising-edge detection on directional input triggers jump.
  • Executes predefined trajectory using STS3032 servos with synchronized write.
  • Includes timed recovery sequence before returning to normal control.

System Integration

FOC Motor Control

  • Uses SimpleFOC for torque-mode control of BLDC motors.
  • Real-time sensor feedback from AS5600 encoders (I2C).

Serial Tuning with Commander

  • Live PID and LPF tuning via UART command interface.
  • Tweak balance behavior, leg responsiveness, yaw dynamics without reflashing