[kitare102]

How we attach 4"x2" colsons (they're on our current shooter prototype) is to put the wheel all the way onto the output shaft and then retain it on the shaft with a 1/4-20 screw into the threaded hole at the front of the shaft and a washer to make sure there's contact with the face of the wheel. Throw some blue loctite on the thread before you put the final bot together and that connection will hold through the competition season.

That being said, the output shaft on a versaplanetary isn't particularly rigid when it comes to side loads farther out on the axle, meaning it might be worth it to come up it a solution to strengthen the output shaft a bit. I've got my own ideas, to be sure.