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Differential drive node?

asked 2017-04-09 20:39:09 -0500

Cerin gravatar image

I have a two-wheeled platform controlled by an Arduino that reports motor encoder counts. So I don't reinvent the wheel, I'm looking for a pre-existing ROS node that can convert those counts into standard odometry and tf messages. Is there a standard ROS package that implements this?

I found this differential_drive project, but it appears to be dead and doesn't have a Kinetic package available.

I also found this differential_drive_controller project, but it appears to be more high-level and doesn't support listening to motor encoders directly. I'd still need to implement a custom node to convert my motor encoder messages to joint messages, so if I need to overcome that overhead, it would make more sense to just implement the odometry reporting myself instead of running two separate nodes in memory.

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answered 2017-04-10 15:56:16 -0500

Mark Rose gravatar image

I've used differential_drive in Indigo and Jade. You cannot install via rpm but can get the source from GitHub and add to your catkin_src. The original code was for Groovy, but the author has incorporated some changes I supplied to make the package more ROS-up-to-date and remove compile warnings for Hydro and above. ( https://github.com/jfstepha/different... )

That said, I no longer use differential_drive for these reasons:

  • I intended to use differential_drive together with rosserial_python to talk to an Arduino-based robot controller. However, rosserial proved unreliable on Arduino-class devices with only 2kb RAM, so I had to abandon that approach.

  • I shifted to using ros_arduino_bridge, which incorporates the functionality that differential_drive supplies, so I no longer needed it.

If you decide to use differential_drive, a few observations:

  • differential_drive incorporates a PID controller in Python to send motor controls via ROS messages. However, the author of differential_drive doesn't recommend that method any more. (From email communication.) He recommends instead putting the PID controller closer to the motor control hardware.

  • differential_drive mixes units at times. For example, motor commands sent by the node are in m/s, while odometry returned from the motor control system is in encoder ticks per second.

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answered 2017-04-10 01:08:13 -0500

I think the best way to do this in order to take advantage of all the goodies ROS has to offer, is to implement an interface for ros_control. You can check the ros_control github wiki for some tutorials. It might seem too much work at first, but once you implement it almost any navigation-related package will be compatible with your robot. Good luck!

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That seems even more complicated than differential_drive_controller, and has features I doubt 'll need. I'm looking for something to implement what ros_control calls the "hardware_interface::RobotHW" node, which ros_control doesn't appear to implement.

Cerin gravatar imageCerin ( 2017-04-10 08:38:22 -0500 )edit

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Asked: 2017-04-09 20:39:09 -0500

Seen: 941 times

Last updated: Apr 10 '17