V-belts don't stay attached to pulley

Arno Goossens wrote:

 

Here's the updated assembly!

Okay, here is what I found and these are things you should embrace in order to improve your modeling skills:

1. Pulley_Small: First feature has two circles in the sketch, but only one is used for the feature.  Cut-Revolve1 has underdefined sketch elements - THIS IS VERY BAD!  Make the angled sides symmetric about a center line emanating from the midpoint of the root line segment and they will be properly constrained.  This whole part could have been more easily made in one feature, a Revolved Boss that correctly defines the profile such as this.

Note in the image above the centerline of the left groove is coincident with the origin.  This conveniently puts an already existing principal plane in the center of this groove, which makes later construction of the belt very easy by selecting this plane.  Also note that the right hand groove uses parallel, collinear and equal length sketch constraints.  This is so that you only have to make changes to one groove and it will be reflected in the other.  Duplicating dimensions is just a recipe for disaster since there are multiple dims that have to be updated and this is often easily missed.

The large pulley has similar problems.

2. On both pulleys it is good to put a sketch on a plane through the center of one of the grooves that only has a circle.  This circle should be the pitch diameter of the pulley.  Label it as such for later use in making the belt.

3. Your assembly model is floating in space.  Fix or otherwise fully constrain something like the box bottom.  Just grabbing and moving anything in your assembly messed everything up.  This is easily avoided if the assembly is anchored and everything is properly constrained.

4. In reality belts are fixed length, therefore it is a better practice to make the belt part definition a driving length.  Leave both pulleys free to rotate and give one of the pulleys a freedom to change its center distance, perhaps constrain the axis of the small pulley to move in an adjusting slot.  When you use the fixed length for the belt SWX will automatically move the pulley where it needs to go to satisfy all the parameters.

Normally I would not put this much time into a student project such as yours, but you indicated you have experience with another CAD system so I felt it important to try to help you improve your path in 3D modeling in general and SWX in particular.  You are a student and just learning, but that is why it is so important to heed this advice now and make good habits from the start:

    ALWAYS make your sketches fully defined.

    Make your models efficiently with few features.

    Make good use of sketch constraints such as mentioned above.

    NAME YOUR FEATURES ON CREATION - this is especially important if your model will have a lot of features, but even more important if someone else will be using your model and needs to understand/change it.

Please accept my comments as helpful and constructive input.  I am only trying to shorten your learning curve to prevent frustrations with your modeling.

Also, you really would benefit from carefully going through the tutorials.