COSMOSMotion treats parts as infinitely stiff, and because of this, can only have one constraint restricting a specific degree of freedom on a part. In situations where there are more than one constraints restricting a specific degree of freedom, we have redundant constraints. The solver automatically removes redundancies before simulating the mechanism. In some cases, degrees of freedom in which you may have expected results, will have no value if the solver removed them.
The classic case is a door with two hinges. Only one joint can restrict the vertical translation of the door (let's assume z is that direction) so that when you plot joint force results, you will not see a z-force component on the second hinge.
If joints are given a specific stiffness (that is, become flexible), the motion in a specific degree of freedom can be resisted by all of the joints with stiffness in that direction. The load on each joint will be a function of the stiffness value.
This approach is still an approximation to taking the true stiffness of the part into account, but it can provide a more realistic distribution of forces than the infinitely stiff case.
In this example, we will use a table top mounted by four bolts to demonstrate the effect of having flexible joints.
Learn more about making joints flexible.
We set up the model with a torque applied at the center of the top that should be equally reacted on all four mounting bolts.
To load the model:
From the COSMOSMotion installation directory, go to Tutorials/flexible_joints_exercise.
Make a copy of this folder to a different location
and then open flexible_joints_exercise_start.SLDASM.
COSMOSMotion informs you which documents will be converted when saved.
The necessary plots and force results are set up so all you have to do is run the simulation.
To run a simulation:
Select the Motion
tab 
.
At the bottom of the Browser, select the Run Simulation button 
.
You should see only two of the joints reacting the load (with the same
magnitude), instead of four. This is because the solver has removed redundancies
(that is, the other joint constraints that were not necessary to define
the movement of the plate).
To run a simulation:
At the bottom of the Browser, select the Delete Results button 
.
Right-click the Motion
Model branch, and then select Simulation
Parameters.
Select Make Joints
Flexible, as shown next.
COSMOSMotion converts all the standard types of joints into custom
bushings with stiffness properties in the directions being constrained
by the joint. For example, a cylindrical joint will be represented as
a bushing with stiffness in every direction, except translate-z
and rotate-z.
Run the simulation again.
The loads are now evenly distributed at the bolt holes.
