🕷️ SpiderBot Simulation - Robot_Bullet_Simulation

A complete simulation of a spider robot (quadruped) using PyBullet for physics and inverse kinematics control. This project offers several control modes and autonomous movements.

📋 Table of Contents

• Features
• Project Architecture
• Installation
• Usage
• Operating Modes
• URDF Structure
• Controls
• Inverse Kinematics
• References

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✨ Features

• Realistic physics simulation with PyBullet
• 3 versions of URDF models (V1, V2, V3) with collision geometries
• Inverse kinematics for cartesian leg control
• 3 control modes :
  • Autonomous mode with trotting gait
  • Manual mode with joint control
  • Cartesian mode for direct foot position control
• Programmed trajectories :
  • Straight-line movement (trot)
  • In-place rotation

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🏗️ Project Architecture

Main Files

spiderbot-simulation/
├── main.py                      # Main entry point
├── robot.py                     # Robot class - kinematics and movement
├── kinematics.py                # Inverse kinematics (IK)
├── interface.py                 # Control interface and debug parameters
├── world_simulate.py            # Simulation and environment management
├── Robot_mesh_urdf_V1/          # Robot model V1 (RobotSpider)
├── Robot_mesh_urdf_V2/          # Robot model V2 (RobotProto)
├── Robot_mesh_urdf_V3/          # Robot model V3 (improved RobotSpider)
└── tools/                       # Utilities (VHACD generator for collision)

Main Classes

Robot (robot.py)

• __init__ : Robot initialization with URDF
• manual_move() : Manual joint control
• manual_cart_move() : Cartesian leg control
• autonomous_move() : Autonomous walking with trot
• update_joint_axes() : Debug display of joint axes

WorldSimulate (world_simulate.py)

• __init__ : PyBullet client initialization, environment setup
• load_world() : Load plane (plane.urdf)
• load_object() : Load robot URDF
• create_heightfield_ground() : Generate variable terrain

Interface (interface.py)

• init_auto() : Parameters for autonomous mode
• init_manual() : Parameters for manual mode
• init_manual_cart() : Parameters for cartesian mode
• end_mode() : Debug parameters cleanup

ik_leg() (kinematics.py)

Inverse kinematics calculation for a leg:

• Input : Target position (x, y, z)
• Output : Joint angles [hip, knee, foot]
• Parameters : Segment lengths (coxa, tibia, tarsus)

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📦 Installation

Prerequisites

• Python 3.8+
• PyBullet
• NumPy
• keyboard

Install Dependencies

pip install pybullet numpy keyboard

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🚀 Usage

Launch the Simulation

python main.py

Debug Mode

To enable debug mode (display joint axes):

debug = True  # In main.py line 13

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🎮 Operating Modes

1️⃣ Autonomous Mode

Activation : Click the "Mode Auto" button in the debug interface

Features :

• ✅ Trot walking (forward/backward)
• ✅ In-place rotation
• ✅ Dynamic leg lifting (70mm height)

Available Parameters :

• Run : Enable/disable movement
• Turn : Enable/disable rotation
• Rotation angle : Target rotation angle (-π to +π)

Gait

• Period : 0.25s
• 4 legs in trot configuration (diagonals)
  • Front-right (AVD) + rear-left (ARG) legs in phase
  • Front-left (AVG) + rear-right (ARD) legs offset by T/2

2️⃣ Manual Mode (Joint Control)

Activation : Click the "Mode Manuel" button in the debug interface

Features :

• 🎯 Direct control of 12 joints (3 per leg)
• Precise movement ranges for each joint

Joints per Leg :

• H (Hip) : Base rotation, ±1.57 rad (±90°)
• V1 (Vertical 1) : First vertical joint, ±1.57 rad
• V2 (Vertical 2) : Second vertical joint, -2.36 to +0.79 rad

3️⃣ Cartesian Mode

Activation : Click the "Mode Manuel Patte" button in the debug interface

Features :

• 🦵 Direct control of foot position (x, y, z) for each leg
• Automatic angle calculation via inverse kinematics

Movement Ranges :

• X : -200 to +200 mm
• Y : -200 to +200 mm
• Z : -200 to 0 mm

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🦴 URDF Structure

Robot Anatomy

The robot has 4 legs (ARD, ARG, AVD, AVG) with each having 3 joints :

Base (Chassis)
├── ARD (Rear-Right)
│   ├── Hip
│   ├── Knee (Tibia)
│   └── Foot (Tarsus)
├── ARG (Rear-Left)
│   ├── Hip
│   ├── Knee
│   └── Foot
├── AVD (Front-Right)
│   ├── Hip
│   ├── Knee
│   └── Foot
└── AVG (Front-Left)
    ├── Hip
    ├── Knee
    └── Foot

Available Models

Version	Name	Usage
V1	RobotSpider	Original
V2	RobotProto	Prototype
V3	RobotSpider	Final

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⌨️ Controls

In the Simulation (PyBullet Debug Interface)

• Mode Buttons : Select desired mode
• Sliders : Adjust parameters based on active mode
• Camera :
  • Right-click + drag : Rotation
  • Right-click + Ctrl + drag : Zoom
  • Right-click + Shift + drag : Pan

Keyboard

• Q : Quit the simulation

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📐 Inverse Kinematics

General Formula

For a leg with segments (coxa, tibia, tarsus), inverse kinematics calculates:

Hip : Base rotation $$\text{hip} = \frac{\pi}{2} - \arctan2(y, x)$$

Knee and Foot : Triangle geometry formed by the segments

Default Parameters

coxa = 60 mm            # Base segment (coxa)
tibia = 76.84 mm        # Intermediate segment (tibia)
tarsus = 128.05 mm      # Terminal segment (tarsus)
offset_foot_angle = 0.15708 rad  # Foot angle offset (~9.5°)

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📚 References

PyBullet Documentation

• PyBullet GitHub
• PyBullet Quickstart

URDF Files

• URDF Format : Unified Robot Description Format
• STL Files : 3D mesh files for visualization and collision

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