Mechanism Design and Mechanism Dynamics > Mechanism Design > Creating Mechanism Models > Connections and Degrees of Freedom > About Redundancies
About Redundancies
Redundancies are excess constraints that do not apply any restrictions to a body's motion. During the assembly process, if you use a constraint set that restricts the motion of bodies in your assembly, and then add another constraint set that affects the same bodies and limits the same degrees of freedom, the second joint is redundant.
If you do not take redundancies into account when performing a Dynamic analysis, you may not get accurate values for measure connection reactions or load reactions.
For example, if you model a door using two pin connections for the hinges, the second pin joint does not constrain the door's motion. The redundancies are ignored (one of the pin connections) by the system when it calculates the analysis. The outcome is incorrect reaction results, although the motion is correct. For complete and accurate reaction forces, it is critical that you eliminate redundancies from your mechanism.
Alternatively, for strictly kinematic problems where you are interested in displacement, velocity, and acceleration, redundancies in your model do not affect the design and performance of the mechanism.
You can control the redundancies in your model by your choice of constraint sets. They must be able to restrict the same DOF, but not duplicate each other. When you decide which constraint sets you want to use, you can use a simple formula to calculate the DOF and redundancies.
By default, the software calculates the DOF and redundancies for the model each time you analyze its motion. To check if your model has redundancies, first run a Dynamic, Static, or Force Balance analysis. Calculate the DOF in the Analysis Definition dialog box when you run a Force Balance analysis. Use the Measure Results dialog box to calculate the DOF and redundancies in your mechanism.