ROS2 VESC Driver for Differential Drive Setup

1. Introduction

A basic python driver for VESC-based differential drive system that runs on ROS2-foxy

I made this tiny script for my robotic platform. The existing VESC drivers at the moment either don't support ROS2 or dont implement CAN chaining (pass command through to a CAN device). In my HW config I have 2x VESC devices connected via CAN. One of those acts as a master and connects to the host via serial (USB-serial).

The image below describes the physical context that this package is developed for.

2. Installation

You may deploy this package either natively or as a docker container,

For native use all you need is to clone the package into your workspace, install dependencies (pyserial) and build it.

cd ros2_ws
colcon build --packages-select ros2_vesc_drv
. install/bash.setup

For use with docker - clone the repo anywhere on target and build the image with

cd ros2_vesc_drv
docker build -t ros2_vesc_drv .

or build it elsewhere and push to / pull from your own docker registry

3. Package Contents

This packages provides a number of nodes and launch scripts to get throught the bring-up of the robot

Nodes:

• vesc_diff_drv - provides basic interface to the VESC controller over a serial connection (usb-serial by default but other things will work too).

• vesc_diff_cmdv_mapper - translates /cmd_vel into differential drive demands

Launch scripts:

• vesc_cmd_vel.launch.py - provides VESC driver for 3x CAN-chained controllers + diamond-steering mixer so that the whole thing could be controlled via /cmd_vel with linear.x for FWD / REW movement and angular.z for rotation
• vesc_with_joy.launch.py - builds on top of vesc_cmd_vel.launch.py but also adds joystic control; additionally requires joy and joy_teleop packages
• joy_teleop.launch.py - a helper launch file to spin-up joy and teleop-joy on a remote host for a scenario where the vesc_cmd_vel.launch is running on the target (robot) and joystick is connected to a host / development computer. Also requires all the related joy packages

3.1 vesc_diff_drv Node

Provides basic interface to the VESC controller over a serial connection (usb-serial by default but other things will work too).

ROS2 Subscriptions:

Topic	Description	Message Type
/vesc_L/duty	Defines set-point for the "Left" motor; interpreted in the context of currently selected control mode (ROS parameter control_mode)	Float32
/vesc_R/duty	Defines set-point for the "Right" motor; interpreted in the context of currently selected control mode (ROS parameter control_mode)	Float32

to test the node you may publish some set-points via terminal:

ros2 topic pub --rate 10 /vesc_R/duty std_msgs/msg/Float32 data:\ 0.05\

The node supports dynamic parameter re-definition. The following parameters are supported:

Parameter	Description	Type	Default Value
serial_port	path to the serial port that VESC master is attached to	String	/dev/ttyACM0
control_mode	selects control mode; may be set to duty, speed or position	String	duty

the table below provides some additional detail to help with the control mode selection:

Control mode	Uses e-brakes	Range
duty	yes	-1.0 to 1.0
current	no	-I_LIM to I_LIM
rpm	yes	RPM_LIM_LOW to RPM_LIM_HIGH

You may want to pre-program those limitters using the vesc_tool

to change a parameter dynamically you may use rqt or terminal like so:

ros2 param set /vesc_diff_drv control_mode "position"

3.2 vesc_diff_cmdv_mapper Node

3.3 vesc_cmd_vel.launch.py Launch Script

3.4 vesc_with_joy.launch.py Launch Script

There is also a launch file that allows for teleoperation using joystick / cmd_vel topic. It implements the graph below:

The launch file has some parameters tuned for my platform (like speed limits) so you may need to tune those things a bit.

ros2 launch ros2_vesc_drv vesc_with_joy.launch.py

3.5 joy_teleop.launch.py Launch Script

4. Using the package

To run the nodes / launch files you may consider the following options:

Runninng a node or launch file from a native package (installed in a ROS2 workspace):

# to run a node use:
ros2 run ros2_vesc_drv <node name from section 3>

# to run a launch script use:
ros2 launch ros2_vesc_drv <launch script name from section 3>

Running the nodes or launch files in a docker container looks very similar to the above thing with only 2 exceptions - for the driver to use the comms you need to pass --device=... to point to the VESC serial file in /dev and also I didn't figure out yet what device I need to pass-through so that the joy package works in a container (but I also don't really need that in my application).

docker run -it --net=host --pid=host --device=/dev/ttyACM0 ros2_vesc_drv:latest ros2 <run or launch> ros2_vesc_drv <launch script or node from section 3>