OpenCR Setup for TurtleBot3

Overview

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OpenCR (Open-source Control module for ROS) is the motor controller and sensor interface for TurtleBot3. This guide covers firmware setup and basic testing.

Installation Steps

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Add ARM Architecture Support

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sudo dpkg --add-architecture armhf
sudo apt-get update
sudo apt-get install libc6:armhf

Set Environment Variables

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export OPENCR_PORT=/dev/ttyACM0
export OPENCR_MODEL=burger

For Waffle:

export OPENCR_MODEL=waffle

Download Firmware

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rm -rf ./opencr_update.tar.bz2
wget https://github.com/ROBOTIS-GIT/OpenCR-Binaries/raw/master/turtlebot3/ROS1/latest/opencr_update.tar.bz2

Extract and Flash

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tar -xvf opencr_update.tar.bz2
cd ./opencr_update
./update.sh $OPENCR_PORT $OPENCR_MODEL.opencr

Key Concepts Explained

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dpkg

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Debian Package Manager:

• Low-level package management
• Install, remove, configure packages
• --add-architecture: Enables cross-architecture packages

armhf

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ARM Hard Float:

• ARM processor architecture
• Uses hardware floating-point unit
• More efficient than software float (armel)

libc6

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GNU C Library version 6:

• Core system library
• Provides standard C functions
• Required for running ARM binaries

Environment Variables

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Why use them:

• Flexibility: Easy to change without editing scripts
• Security: Credentials not in code
• Automation: Scripts can read values

Testing OpenCR

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Physical Setup

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1. Connect power to OpenCR
2. Place robot on flat ground
3. Ensure wheels are free to move

Push Button Test

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OpenCR has test buttons:

LED Indicators

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Troubleshooting

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Permission Denied

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sudo chmod a+rw /dev/ttyACM0

Or add user to dialout group:

sudo usermod -a -G dialout $USER
# Logout and login again

Device Not Found

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Check connection:

ls /dev/ttyACM*

If not listed:

• Check USB cable
• Try different USB port
• Restart OpenCR

Firmware Flash Failed

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Error: Cannot open device

Solutions:

1. Check port name matches actual device
2. Ensure no other program using port
3. Verify USB connection

OpenCR Commands

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Reset OpenCR

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Press RESET button or:

# From ROS
rosservice call /motor_power "state: false"
rosservice call /motor_power "state: true"

Check IMU Data

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rostopic echo /imu

Motor Status

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rostopic echo /joint_states

Advanced Configuration

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Custom Firmware

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For development:

# Clone repository
git clone https://github.com/ROBOTIS-GIT/OpenCR.git

# Open in Arduino IDE
# Select OpenCR board
# Upload sketch

Calibration

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IMU calibration:

rosrun turtlebot3_bringup turtlebot3_motor_calibration.py

Hardware Connections

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OpenCR
├── USB → Raspberry Pi
├── Dynamixel → Motors (L/R)
├── LDS → Laser sensor
├── IMU → Internal
└── Power → 11.1V LiPo