Problems with robot modeling in model.sdf

edit

It appears the joints of your robot do not have controllers that apply torques/efforts to them. You could write your own plugin for applying such forces (see this gazebo tutorial). A simpler option is the use of existing controller plugins, similar to how it is done on the drc robot. That model is a URDF model however, so I am not totally sure you can apply things to your pure SDF. The simplest option is to use per joint position PID controllers as it is done in the atlas_position_controllers.launch launch file. This gives you one '/[joint_controller_name]/command' topic per joint that listens to std_msgs/Float64 position commands. Another option is the use of of whole body trajectory action controller as it is currently done in the default atlas.launch file, which in turn includes atlas_bringup.launch.

It's recommended you have a look at the drcsim tutorials, those show some basics of how a robot like yours can be controlled (no fancy walking or whole body control available though, all drc teams are busy working on that ;) ).