How to control a single wheel(continus joint)

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You could try writing your own plugin.

It should consist of a cmd_vel subscriber (or whichever topic you use for the velocity commands) and the part where you apply the command on your wheel (so for example either a setVelocity command or if you use ros_control then a publisher for the command topic).

If you're not familiar with writing plugins then I suggest you start with the tutorials. http://gazebosim.org/tutorials/?tut=p...

Do check the source code of diffrive_plugin as it has the necessary components you need.