If you're looking for a crafty project to tackle with your toddler, this rubber band-powered ball launcher might be just the thing. It's pretty straightforward for anyone with a drill, access to rubber bands, and a toddler who likes to see things go flying.
I took inspiration for this project from something similar I saw at a kid's birthday party in Vermont where the parents had hired The Big Blue Trunk. The owner made party games himself and I thought it was a really interesting contraption. I took some mental notes thinking it might be fun to make one ourselves. I had a buddy visiting one weekend and we decided to take on the project.
The first step was to draw out what we were thinking it might look like. We wanted it to be free-standing, so we would need a base and it had to be able to shoot a tennis ball. Here's our very scientific drawing of what we had in mind:
I was pretty sure the original I saw at the party was made from PVC pipe so we picked some various sizes up at our local big box hardware store. We had to make sure that the tube was big enough for a tennis ball, but also big enough to accommodate a cup or something to propel the ball out, as well as rubber bands. We tried all kinds of materials like surgical tubing, but heavy duty rubber bands seemed to work the best.
Secondly, we had to figure out what we would use to propel the ball out. I snagged an old piece of pretty rigid tupperware that fit really well into the opening. We had to do some surgery with a dremel tool, but it turned out to be the perfect size for our contraption.
Here you can see how it's been trimmed down to fit inside the tube. Be sure you're using something stiff since a bunch of pressure will be put on it when you pull back on the launching string.
We drilled holes in either side of the cup as well as one in the bottom. We also used washers to keep the rubber bands from pulling through our holes on either side of the cup. The same kind of washers were used on the outside of the PVC tube where the rubber bands popped out. It's important that the holes in the pipe and the cup line up pretty well, so when you pull back the string, the cup stays pretty straight.
Next step was to build the simple firing mechanism. The key here was to make sure that the rope pulling down on the cup is pulling straight down the tube. In the picture below, you'll see a piece of PVC pipe crossing the tube held in place by some rubber bands just above where the pull string comes out. This is an important step to ensure that the cup stays in the center of the tube when you pull the firing rope.
Then, we had to make the stand so that kids didn't have to hold the thing up to shoot a ball. Using the smaller PVC diameter along with two elbows, we simply drilled through the pipes and the bigger PVC tube, fished some long bolts through, but some PVC glue on the joints, and we were almost done. The last step for the stand was to put a string from the base to the tube to ensure the launch angle was the same every time.
Finally, we fished the pull rope through a spare piece of smaller PVC to make a handle so it would be easier for little hands to get the force needed to fire a ball. It works great!
Here's a really poor quality video of my little man shooting a ball like the ones you would find in a kids ball bit.