Thanks for posting a very nicely illustrated question. I am on the System Modeler development team, and very interested in understanding what we can do better to help users "debug" this sort of problems. Of course, I also wish things were simple enough that one would never need to reach out for help, but I am well aware that this is not always the case when working with MultiBody models.

Some observations to start with:

• Your model has a sequence of three revolute joints to give the cube its three degrees of freedom. However, such a configuration has the danger of ending up in singular configurations. Maybe you are aware of this and can make sure you don't end up there, but a Spherical joint typically solves this problem in a better way.
• It surprises me that the only nonlinear system seen in the equation browser has been reduced by tearing to just a single angular variable. I mean, the symmetry of the problem's three degrees of freedom suggests to me that none of the angles should be possible to solve before any of the others, and since the three angles are not algebraically constrained, the nonlinear system where one angle is solved shouldn't be possible to tear to size 1. However, maybe the physical symmetry is lost in the sequence of revolute joints, so I could be wrong about this.
• My gut feeling is that one could expect angles to be computed by integration of angular velocities rather than being solved from nonlinear systems of equations. Have you checked whether the selection of states looks sensible?

Thank you for such a quick reply, and your tips, in fact the error was using the three revolute joints...once switching to a Sphericaljoint as you suggested the problem went away, I can now simulate and test as I please....Though I am now having another problem, I would like to import the model into Mathematica to derive some control values and experiment there...however, when importing just the physical model with the three inputs it has unconnected, Mathematica complains the model is unbalanced and and nothing can be done.

However, when importing with just a Const.k =0 connected to the models inputs, it can simulate the model, but the outputs and inputs appear empty and it refuses to give a statespacemodel that has any inputs or outputs...(outputs I expect to be around 15 and inputs 3...should I ask a new question or are you aware if models have to be specially designed for inputs and outputs when importing to Mathematica?

Thank you again for the initial help!

Thank you for the explanations! Once I get around to working on it again, I will definitely report back my findings, Though it seems like that is the problem, namely lack of proper Real.Output