One motor runs in wrong direction with diff drive

[davidstart09]

I have probably missed something but the problem i have is with a diff drive robot using ros2 control under ros2 foxy. rviz shows wheels rotating correctly but when going forward both motors rotate in the same direction which means one wheel is going in the wrong direction due to motors bing mirrored.

[davidstart09]

Also when trying to rotate robot the motors don't really move

[borongyuan]

Hi, if you set up transformations according to the convention, the reference frames of wheels should all be parallel. This means that all wheel joints should rotate in the same direction as the robot moves forward.

Of course, if you use a symmetrical motor layout, the motors on both sides should rotate in opposite directions. However, the ros2_control framework hopes that upper-level developers can look at problems from the perspective of joints, without considering the specific implementation of actuators. There was a PR (#23) that added the rotation direction configuration, but I don't quite agree with this approach. The mapping between actuator and joint space should be handled by transmission interface.

[avibrown]

Hi, if you set up transformations according to the convention, the reference frames of wheels should all be parallel. This means that all wheel joints should rotate in the same direction as the robot moves forward. Of course, if you use a symmetrical motor layout, the motors on both sides should rotate in opposite directions. However, the ros2_control framework hopes that upper-level developers can look at problems from the perspective of joints, without considering the specific implementation of actuators. There was a PR (#23) that added the rotation direction configuration, but I don't quite agree with this approach. The mapping between actuator and joint space should be handled by transmission interface.

Hi,

Could you please offer a clear guide as to how to use transmissions? For someone new to this stuff it is pretty hard to grasp at first. I personally have been stuck on this issue for hours trying to get the wheel directions to match those of my physical robot (they are reversed as in the case of OP).

If you can show a simple setup for a differential drive robot it would be super helpful. Thank you!

[borongyuan]

Sorry for the late reply. The ros2_control_demos packages are restructed and have quite a few updates. A demo for transmission interface was added in ros-controls/ros2_control_demos#226. I'll check compatibility and update demos later.

[MichaelT800]

I have the same problem,
when I change right_wheel_radius_multiplier to -1 in the file diff_drive_controller.yaml then the motor can rotate in reverse
and
-0.1 will respond correctly to the speed control according to the 1:10 reduction ratio.
Hope this helps!