DC motor with encoder interfacing using ROS serial

Project has been built for Arduino Nano

Equipment required

1. Arduino Uno or Nano - 1 nos
2. DC motor with encoder - 2 nos (I have used SPG30E-200K DC Geared Motor with Encoder)
3. L298 or L293 motor driver - 1 nos

Steps to code

1. Include the required header files
2. Declare variables for publishing encoder ticks
3. Instantiate a ROS Publisher to publish the motor encoder ticks
4. Instantiate a ROS subscriber that subscribes to the topic /cmd_vel
5. Within the Arduino setup function :
   • Set the pin modes
   • Initialize the baud rate
   • Initialize the node
   • Initialize the subscriber for command velocity
   • Initialize the subscriber for resetting encoders
   • Advertise the left and right motor encoder publishers
6. Within the Arduino loop function :
   • Assign data values to encoder tick publisher
   • Process the subcriber callback (nh.spinOnce())
   • Add a small delay

Other functionalities are implemented in the header files in the include folder

Motor.h

• Functions for moving the bot : forward, backward, turn left, turn right, stopping
• cmd velocity call back function

Encoder.h

• Interrupt functions for left and right encoders
• Encoder reset function

Config.h

• Pin declarations : Arduino pins connected to motor, PWM pins, Encoder pins

Additional Resources

• DC motor interfacing with ROS serial
• Configure VS Code for rosserial_arduino
• Video tutorial - Configure VS Code for rosserial_arduino

Steps to run the code

1. Launch roscore in a terminal

roscore

2. In another terminal type in following to launch a rosserial connection with Arduino

rosrun rosserial_arduino serial_node.py _baud:=115200

3. In yet another terminal run teleop_twist_keyboard to control the motor. Since we have interfaced only one motor we can verify the following functionalities - bot_forward, bot_backward and bot_stop. The bot_left and bot_right functionalities can be verified by interfacing one more motor.

rosrun teleop_twist_keyboard teleop_twist_keyboard.py

4. Launch another terminal and echo the motor encoder tick topics

rostopic echo \left_encoder_ticks
rostopic echo \right_encoder_ticks