Apply the Constraints to the Piston and Crank

1. Click the Home icon above the ViewCube for an isometric view of the model.
2. With the Selection Shape Point or Rectangle and Selection Select Surfaces commands active, click one of the two cylindrical surfaces at the outside diameter of the piston.
   • Hold down the Ctrl key and click the remaining outside diameter surface. The piston should appear as shown below.

     

3. Click Setup Constraints General Constraint.
   1. Activate the Tx and Tz checkboxes. The piston is only free to translate in the Y direction.
   2. Click OK.
4. Right-click the Part 3 heading in the browser (tree view) and choose Select Related Surfaces. All of the surfaces of Part 3 are now selected. 
5. Click Setup Constraints General Constraint.
   1. Activate the Tx checkbox.
   2. Click OK. The crank is free to move only in the Y and Z directions.  Though not absolutely necessary, this constraint stabilizes the crank by preventing any twisting or bending that might occur from flexure of the joints. It also makes convergence of the solution a little easier, and therefore speeds up the simulation.  

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