Practise - Animate constraints

If you have practised sketcher long enough, animating constraints should be an easy thing to do. And there are many ways to do this. In this particular exercise, we are basically creating four separate profiles within the same sketch, the DOF (Degree of Freedom) of these profiles is not restricted in anyway and they can move relatively freely with respect to each other at first. Subsequently, the aim is to animate piston profile, crank profile and connecting rod profile movement within a cylinder and case profile. Therefore, they are applied constraints keeping in mind the motion they would undergo. Below you can see the profiles that are created.

Four profiles created within a sketch

The four parts would be:

• Engine / case outline (with space for movement of other sketches, this would either be fixed or would be constrained appropriately
• Crank sketch outline, 
• Connecting rod sketch outline,
• Piston outline that reciprocates within the cylinder sketch. 

Creating Sketches 

First, create a 2D-sketch that resembles a connecting rod and then a crank that rotates around the centre.
Afterwards, create the outline of a cylinder and space within which the crank will rotate and dimension it around the origin so that it does not move in anyway. Also, create the square shape that resembles a piston within the cylinder outline so that it can move just up and down and have no other DOF (Degree of Freedom). Subsequently, dimension them in the way such that they maintain following relationships.

• The crank should be able to rotate around the origin.
• The rod should be connected to the piston at one end and crank’s end at the other and should be able to move in the plane. 
• The outline of 2D piston profile should have only translation DOF. In the end, you can provide an angle constraint to the crank with reference to the Vertical or Horizontal axis. This would fully constrain the sketch and would let you animate the angle constraint. 

Use the ‘Animate Constraint’ tool to animate the angle constraint that would animate the 2D sketch mechanism. Below you can see how it will animate.

Animate constraint applied

Note: The dimensions and sketches are for illustration only. Since the sketch is parametric, you can modify the dimension as per requirement.

If you have any questions or comments, feel free to leave them below.