How to apply torque to a joint in code?

edit

is this tutorial suitable for gazebo 8? I keep getting errors: ```SetLinkVelocityPlugin.cpp:51:65: error: call of overloaded```

Ah sorry about that, the tutorial needs to be updated for Gazebo 8+, we will probably get to it in the coming days during the tutorial party: https://community.gazebosim.org/t/gazebo-9-tutorial-party

the above link is private. also is there a way i can participate in this tutorial party?

Oh sorry, this website adds garbage to the end of links, try copying and pasting the URL in the browser

do you know where i can find the updated tutorials?

The link I posted before is the latest, i.e. http://gazebosim.org/tutorials?tut=set_velocity <- this one

I'm not so sure the tutorial has been updated. I keep getting this "use of undeclared identifier" error around the math and physics engine libraries when i used gazebo8 or 9 but 7 runs fine.