Wheel Going in the Wrong Direction – RVIZ2 and FoxGlove

Hi everyone,

I hope you’re having a good break! I’m currently following this tutorial and messing around with a diffdrive robot. After making a few changes I noticed that my simulations were playing up. Strangely, the robot itself was still working perfectly fine.

The problem I was having was that even though my robot was driving forward the simulations seemed to think that the left wheel was going backwards. Initially I suspected this was an issue with my robot’s definition but even when returning to a known working state the issue persisted.

Eventually, I realised that this meant it had to be a hardware issue. I am using an Arduino and two L298N motor controllers for the motors that run my wheels. The arduino then publishes my encoding counts over serial.

To debug this setup, I used miniterm to communicate with the arduino and view the serial output. To get this going I had to track down which serial port had the arduino connected:

ubuntu@ubuntu:~/robot_ws$ lsusb
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 006: ID 1a86:7523 QinHeng Electronics HL-340 USB-Serial adapter

Alternatively, ls /dev/ttyUSB* would also work. I also needed the baud rate which is set to 57600. This allowed me to connect, move the motors forward and also see the encoding counts:

ubuntu@ubuntu:~/robot_ws$ miniterm -e /dev/ttyUSB0 57600
--- Miniterm on /dev/ttyUSB0 57600,8,N,1 ---
--- Quit: Ctrl+] | Menu: Ctrl+T | Help: Ctrl+T followed by Ctrl+H ---
e
0 0
o 255 255
OK
e
-5531 5572
e
-8120 8222
e
-8120 8222

The issue became obvious with the left wheel outputting a negative value. The fix for this was pretty simple. Reversing the pins outputting the encoding count for the left wheel reverses the counter. Re-running the miniterm test showed both wheels with a positive count:

ubuntu@ubuntu:~/robot_ws$ miniterm -e /dev/ttyUSB0 57600
--- Miniterm on /dev/ttyUSB0 57600,8,N,1 ---
--- Quit: Ctrl+] | Menu: Ctrl+T | Help: Ctrl+T followed by Ctrl+H ---
e
0 0
o 255 255
OK
e
8146 8211

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