Made a 7 dof robot arm in Gazebo. Want the joints for the arm to act like electric motors and not free fall

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Thanks Peter for the advice. What I am trying to validate are contact dynamics in Gazebo while passing torque based commands using Matlab. I am familiar with ROS control and have used its control plugins before for position and velocity on previous occasions outside of Gazebo. My colleagues would want to use ROS as least as possible. Are there any options within Gazebo to allow me to achieve the same results?

Yea for sure. the ROS thing are just heavy wrappers of the existing PID functionality in all gazebo joints. The easiest way (in my opinion) is to send gazebo::msgs::JointCmd. Fill out the joint name, PID, and target and it will just work. You say matlab... gazebo plugins must be C++, and you need C++ to send gazebo msgs. But assuming you can get some C++ going somewhere then it shouldn't be hard.

Also, one thing to help with the free-fall thing is damping. Try setting damping (try things between 1-20 depending on how heavy your links are). I sometimes just set damping really high to simulate joints where the motor doesn't backdrive easily, but that isn't really an accurate way of doing it

Ok, looking through the tutorials for control model plugins in Gazebo (http://gazebosim.org/tutorials?tut=guided_i5) I do not see a use case for gazebo::msgs::JointCmd. But can I assume that if I create a Gazebo node (in c++) to publish commands using that message type I do not have to write a gazebo control plugin in c++? For the Matlab side there is a way to convert the functions into c++ programs so the torque outputs can be handled by the gazebo control plugin.

correct. The PID interface is already build in for all joints in gazebo. As long as you publish that message it will work. the joint panel hiding on the right side of gazebo uses the same thing. check `/gazebo/default/my_model/joint_cmd`.