How can I model a drivetrain with two mechanical motion sources (competing) on one axle so I can capture the torque and speed on the shaft accurately?

I have a system where an environment causes motion on a device and I want to control that motion with a DC motor. I will have competing torques and forces.

I tried structuring the model so that the environment source is input from the workspace and fed through either an ideal angular velocity source or an ideal torque source, but the ideality overrides the DC motor contribution. No good.

Is there an existing example that I can refer to?

I am using SimScape, integrating elements from Mechanics and Electronics and Driveline.