Neil,
5.0
[:0:0-0:0] Notification: Forcing static selection of states. If this leads to problems during simulation turn on dynamic state selection.
[:0:0-0:0] Notification: The following variables are selected as states: model.prismatic12.s, model.prismatic12.v, model.revolute23.phi, model.revolute23.w, model.revolute34.phi, model.revolute34.w, model.revolute45.phi, model.revolute45.w, position.phi, position.w, position1.s, position1.v
[:0:0-0:0] Warning: Start value is assigned for variable: model.prismatic12.s, but not used since it is solved from an equation or from a linear system..
...
5.1
[:0:0-0:0] Notification: Forcing static selection of states. If this
leads to problems during simulation turn on dynamic state selection.
[:0:0-0:0] Notification: The following variables are selected as
states: model.prismatic12.s, model.prismatic12.v,
model.revolute23.phi, model.revolute23.w, model.revolute34.phi,
model.revolute34.w, model.revolute45.phi, model.revolute45.w,
position.phi, position.w, position1.s, position1.v
[:0:0-0:0] Notification: The initialization problem is underdetermined, the
following variables where chosen to be initialized from their start
values: model.revolute45.w, model.revolute34.w, model.revolute23.w,
model.prismatic12.v, position1.v, position.w.
[:0:0-0:0] Warning: Start value is assigned for variable: model.prismatic12.s, but not
used since it is solved from an equation or from a linear system..
...
Something changed in the algorithms behind the numerical integration from 5.0 to 5.1.
The good news is that I managed to fix it. It was not possible to fix initial values, but changing the initial guess value solved it.
The configuration of some closed loops in the model allow for two possible solutions, one in the upper half-plane and the other in the lower half-plane. I had an initial relative angle value for a revolute joint that was obtained from the Mathematica model, this value is the exact solution and it is double checked, it corresponded to the solution for the upper half-plane. This value was set as the initial guess for the revolute joint in the SystemModeler model, but it made the solver find the solution for the lower half-plane (which is really far away). Changing slightly the value made it find the upper half-plane solution again. Weird.
Regards,
Jose