Mytra Robot Guide Wheel Spacing Analysis

A Python simulation and web-based analysis tool for evaluating the stability of warehouse robots traveling on rails, specifically analyzing the effect of guide wheel spacing on ping-ponging behavior.

Overview

This simulation models a Mytra warehouse automation robot with the following characteristics:

• Robot mass: 500 lbs (227 kg)
• Max payload: 3000 lbs (1361 kg)
• Max speed: 1.5 m/s
• Acceleration: 0.75 m/s²
• Guide wheels: 70mm wide, maintaining alignment on rails
• Movement: Single-axis motion (X or Y direction)

The simulation answers the critical question: How much spacing can be allowed between the bot's guide wheels and the vertical rail flanges before the bot starts ping-ponging (oscillating) while trying to drive straight?

Features

• Physics-based simulation using ODE integration
• Multiple spacing analysis (5mm, 10mm, 13mm, 20mm, 30mm, 40mm, 100mm, 200mm, or custom values)
• Stability detection to identify ping-ponging behavior
• Interactive web dashboard with real-time visualization
• Comprehensive analysis including:
  • Lateral position over time
  • Angular orientation tracking
  • Phase plots (position vs velocity)
  • Oscillation frequency analysis
  • Maximum deviation metrics

Installation

1. Install Python 3.12

2. Install Poetry (if not already installed):

curl -sSL https://install.python-poetry.org | python3 -

3. Install project dependencies:

poetry install

4. Activate the virtual environment:

poetry shell

Usage

Web Interface (Recommended)

Launch the interactive web dashboard:

poetry run python app.py

Or if you're in the Poetry shell:

python app.py

Then open your browser to http://localhost:8050

The web interface allows you to:

• Configure spacing values to test
• Adjust simulation duration
• Set initial misalignment angle
• View interactive graphs and analysis results
• Compare multiple spacing scenarios

Command Line

Run the simulation directly:

poetry run python robot_simulation.py

Or if you're in the Poetry shell:

python robot_simulation.py

This will run a test simulation with default spacing values (5, 10, 20, 30, 40 mm) and print results to the console.

Simulation Model

The simulation models:

1. Robot Dynamics: Mass, inertia, and motion constraints
2. Guide Wheel Contact: Spring-damper contact forces between guide wheels and rail flanges
3. Friction: Frictional forces opposing lateral motion
4. Coupling Effects: Interaction between lateral motion and angular orientation

Key Parameters

• Contact Stiffness: 1e6 N/m (stiff contact between wheels and rails)
• Contact Damping: 1000 N·s/m (damping to prevent excessive oscillations)
• Friction Coefficient: 0.3 (between guide wheels and rail flanges)

Stability Analysis

The simulation detects ping-ponging behavior by:

• Counting zero crossings in lateral velocity
• Analyzing oscillation frequency
• Tracking amplitude growth over time
• Comparing maximum deviations to spacing tolerance

Results Interpretation

• Green bars/curves: Stable behavior (no ping-ponging)
• Red bars/curves: Unstable behavior (ping-ponging detected)
• Oscillation Frequency: Higher values indicate more rapid oscillations
• Max Lateral Deviation: Should be compared to spacing tolerance

Customization

You can modify simulation parameters in robot_simulation.py:

• RobotParams: Physical robot parameters
• RobotSimulator: Contact force models and dynamics
• contact_stiffness, contact_damping, friction_coefficient: Contact parameters

Technical Details

The simulation uses:

• scipy.integrate.odeint: For numerical integration of the system dynamics
• Dash/Plotly: For interactive web visualization
• NumPy: For numerical computations

License

This is a simulation tool for analysis purposes. Modify as needed for your specific use case.