gbarbarov / serial_motor_demo

ROS/Arduino Serial Motor Demo

This is demonstration of a ROS 2 interface to an Arduino running differential-drive motor control code.

The corresponding Arduino code can be found here, which is itself a fork of this repo, which also contains a similar implementation for the ROS/Python/Client side (ROS 1 though).

Components

The serial_motor_demo package consists of two nodes, driver.py and gui.py. The idea is that the driver can be run on an onboard PC inside a robot (e.g. a Raspberry Pi), interfacing with the lower-level hardware. The driver exposes motor control through ROS topics (see below), which are to be published by the user's software.

The GUI provides a simple interface for development and testing of such a system. It publishes and subscribes to the appropriate topics.

Driver configuration & usage

The driver has a few parameters:

• encoder_cpr - Encoder counts per revolution
• loop_rate - Execution rate of the Arduino code (see Arduino side documentation for details)
• serial_port - Serial port to connect to (default /dev/ttyUSB0)
• baud_rate - Serial baud rate (default 57600)
• serial_debug - Enables debugging of serial commands (default false)

To run, e.g.

ros2 run serial_motor_demo driver --ros-args -p encoder_cpr:=3440 -p loop_rate:=30 -p serial_port:=/dev/ttyUSB0 -p baud_rate:=57600

It makes use of the following topics

• motor_command - Subscribes a MotorCommand, in rads/sec for each of the two motors
• motor_vels - Publishes a MotorVels, motor velocities in rads/sec
• encoder_vals - Publishes an EncoderVals, raw encoder counts for each motor

Test from terminals Terminal 1 : ros2 topic echo /encoder_vals Terminal 2 : ros2 topic pub /motor_command serial_motor_demo_msgs/msg/MotorCommand "{mot_1_req_rad_sec: 1.0}"

GUI Usage

ros2 run serial_motor_demo gui

Has two modes, one for raw PWM input (-255 to 255) and one for closed-loop control. In this mode you must first set the limits for the sliders.

USB permission

sudo chown username /dev/ttyUSB0

USB serial converter conflicts

https://bugs.launchpad.net/ubuntu/+source/brltty/+bug/1990189

• sudo systemctl stop brltty-udev.service
• sudo systemctl mask brltty-udev.service
• sudo systemctl stop brltty.service
• sudo systemctl disable brltty.service

TODO

• Add service for encoder reset
• Add service for updating PID parameters
• Stability improvements
• More parameterisation