README.md

System Architecture Documentation

Overview

The bipedal robot walking system is built on a force-aware control architecture that maintains stability through continuous force distribution monitoring and adaptive walking pattern generation.

System Components

1. Robot Model (URDF)

simple_biped_stable.urdf
├── Base Link (Torso)
├── Left Leg
│   ├── Hip Joint (Revolute)
│   ├── Knee Joint (Revolute)
│   └── Ankle Joint (Fixed)
└── Right Leg
    ├── Hip Joint (Revolute)
    ├── Knee Joint (Revolute)
    └── Ankle Joint (Fixed)

2. Control Architecture

Walking Controller
├── State Management
│   ├── Robot State Monitor
│   ├── Force Distribution Monitor
│   └── Stability Monitor
├── Motion Planning
│   ├── Walking Pattern Generator
│   ├── Inverse Kinematics Solver
│   └── Trajectory Optimizer
└── Control Execution
    ├── Joint Position Controller
    ├── Force Feedback Controller
    └── Emergency Stop Manager

Key Algorithms

1. Force Distribution Control

def _adjust_com_position(self):
    """
    Adjusts the Center of Mass position based on force feedback:
    1. Measures force distribution between feet
    2. Calculates required COM adjustment
    3. Applies smooth transition using exponential scaling
    4. Verifies force ratio improvement
    """

2. Walking Pattern Generation

def generate_walking_pattern(self):
    """
    Generates walking patterns with:
    1. Pre-walking stabilization phase
    2. Weight transfer phase
    3. Swing leg trajectory
    4. Landing position optimization
    """

3. Inverse Kinematics

def inverse_kinematics(self):
    """
    Calculates joint angles using:
    1. Geometric approach for leg chain
    2. Joint limit verification
    3. Singularity handling
    4. Solution optimization
    """

Data Flow

1. Force Sensors → Force Distribution Monitor
2. Force Monitor → COM Adjustment Calculator
3. COM Calculator → Joint Position Controller
4. Pattern Generator → Trajectory Optimizer
5. Trajectory Optimizer → Joint Controller

Control Flow

graph TD
    A[Initialize] --> B[Reset to Stable Pose]
    B --> C[Force Distribution Check]
    C --> D{Force Ratio OK?}
    D -->|Yes| E[Start Walking Pattern]
    D -->|No| F[Adjust COM]
    F --> C
    E --> G[Execute Step]
    G --> H{Emergency Stop?}
    H -->|Yes| B
    H -->|No| G

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Performance Characteristics

1. Force Distribution

• Target ratio: 0.85
• Acceptable range: 0.75 - 0.95
• Convergence time: < 2.0s

2. Walking Parameters

• Step length: 0.08m
• Step height: 0.04m
• Cycle time: 1.2s
• Startup time: 2.0s

3. Stability Metrics

• Maximum pitch deviation: ±5°
• Minimum ground force: 180N
• Force ratio convergence: 0.800

Safety Systems

1. Emergency Stop Conditions

• Force ratio outside range
• Excessive pitch deviation
• Zero ground contact
• Joint limit violation

2. Recovery Procedures

• Reset to stable pose
• Force redistribution
• Gradual motion resumption

System Integration

1. PyBullet Integration

class URDFWalker:
    """
    Handles PyBullet simulation interface:
    1. Robot state management
    2. Physics simulation
    3. Contact point handling
    4. Force measurement
    """

2. Control Interface

class WalkingController:
    """
    Main control interface providing:
    1. High-level walking commands
    2. State monitoring
    3. Safety management
    4. Performance logging
    """

Future Extensions

1. Planned Improvements

• Dynamic gait adaptation
• Terrain awareness
• Energy optimization
• Learning-based control

2. Integration Points

• ROS interface
• External sensor integration
• Remote control interface
• Data logging system

System Requirements

1. Hardware Requirements

• CPU: Multi-core processor
• Memory: 4GB+ RAM
• GPU: Optional, improves simulation speed

2. Software Requirements

• Python 3.12
• PyBullet
• NumPy 2.x
• Ubuntu 22.04+

Error Handling

1. Common Failure Modes

• Force distribution divergence
• IK solution failure
• Joint limit violations
• Simulation instability

2. Recovery Strategies

• Automatic pose reset
• Adaptive step adjustment
• Force-based stabilization
• Emergency stop protocol