You can use Simscape Multibody (the new name for what was SimMechanics) as a two-step process.
Joints in the package generally allow for one of two inputs to be used - force/torque or position. If you choose to provide joint torque, then the resulting output motion is calculated by the dynamics of the system. If you choose to provide joint position, then Simscape calculates the force/torque required to achieve that motion, then applies that to the system dynamics.
The process I would use for designing would go something like this:
- Create a motion profile that you deem is representative of the tasks the robot is supposed to perform.
- Calculate the inverse kinematics to get the required joint angles to achieve the motion profile.
- Use the joint sensors 50k4 mentioned to trend/plot the joint forces and torques required to achieve your motion profile.
- Choose the peak force/torque for each axis of motion, add some performance margin, and choose actuators that at least provide that performance.
- Generate a model for the actuators you selected. This model includes whatever actuator dynamics there are along with whatever input conditioning you're expecting to use. For example, how are you expecting to have the actuators in real life track joint angle? PID control of angle error? That's what you model.
- Replace your ideal multibody joints with your detailed actuator models.
- Re-run your simulation and verify you're getting the performance you want.
Important to note - try to model weight and bulk as accurately as you can. Masses and inertias can, in some instances, have a very dramatic and negative impact on performance.