I and my Den of Cub Scouts WEBELOS built this little gem about a week ago. I actually built a prototype ahead of time so I could have a plan of attack for directing them through it. It is made almost entirely of Popsicle sticks and tape. The cup is made of paper and obviously there’s the rubber band to make it work. I used 2 inch packaging tape which makes the joints a little stronger, rather than the Scotch tape shown in the pictures.
When completed, it’s actually strong enough to fling a marble a decent distance, and I didn’t even try to seek out an optimal rubber band. Makes for a good half-hour project that kids can do with a little direction. The good thing is the same building procedures are repeated several times over and the only skill required it the ability to wrap tape around the sticks. So I simply demonstrated how to assemble a part and then told them “Do that X more times.”
It’s perfect for completing part of the Engineering WEBELOS Acitivity Badge requirement.
Full directions are here.