The Rubber Band Gun

This is the gun solution that was seen as the best choice from the group of Geoff Holden, and Nicholas Howlett. The gun was chosen over our other ideas because of its simplicity in being easy to load and to manufacture.

The hardest part to make was the sprocket. You have to drill eight holes in it at equal spaced intervals, to put the spokes in. You also have to drill a hole through the centre in order to screw it to the handle. In the handle you drill out a section on an angle and put in a small cylinder in its place to rest the front of the elastic on. There is also a section that is to be milled out to put the sprocket in. A hole has to be drilled in this section where you want the centre of the sprocket to be. After the handle and sprocket are made to the above specifications you only need four more things that you can go buy at any hardware store: a carriage bolt, wing nut, washer and friction washer. Put the bolt in through the hole in the handle. Next put the friction washer on followed by the sprocket. The friction washer is there to provide friction so the wing nut doesn't have to be as tight. Next put the washer and finally the wing nut. The gun is now assembled.

Now that the gun is together it is now the explanation of use. You put the first elastic around the front notch and pull it back around a spoke. You then wind the wheel back and repeat the procedure with the next spoke. There is enough space to do this for seven elastics. The nut keeps it tight so that the sprocket will only move when you pull the trigger, which is the spoke sticking out by handle. At a certain point in the revolution of the sprocket the spoke can not hold the elastic bands. This is when you get one to fire. The other feature is that if you loosen the nut after it is loaded you will get a rapid-fire gun.

In the process of building the gun, we were able to test for the optimal barrel length that would not break the elastic bands. We found this to be about 290mm from the centre of the sprocket.

When the gun was finished we discovered another small flaw, as you fire, the sprocket gets tighter to turn. We found the cause of this problem to be the hex-head bolt we were using had dug itself into the handle. We then tried a carriage bolt and found that its round head was still dug in, but was still able to spin.

We also made a website about the gun and its design. We included the digital photos we took of the gun, and a VRML model. The website is located at http://www.engr.mun.ca/~holden/rubberband/