Your system needs two degrees of freedom:
- Base to motor shaft
- Rotational deflection of motor shaft
You need two separate Revolute Joints to model this system.
Attached is a model where I have put the two degrees of freedom within the "Base" block so that it could reuse the parmeterization from the mask. The torque input is applied directly to the revolute joint (no extra Simscape blocks are needed).
--Steve