In my physics classroom we study projectile motion. Accurate projectile launchers with consistent results are very expensive ($200+). Because of this, I find that I have many students working with few launchers, diminishing the overall experience.
I have designed a launcher that I have been able to create for my classroom that costs less than $5 in materials. Aside from plastic, you will need a large spring ($0.80, I used menards part#88228, 13/16 x 3-1/4 compression spring), and a 5 inch section of 1" schedule 40 PVC pipe.
To launch, a paperclip is used to hold the plunger back. A swift yank will release the plunger, and your projectile should be launched. I used a 1/2" ball bearning, and I found that the projectile would travel around 11 feet, with an error of around 6 inches.
Some of the troubles I ran into, that I expect you will also find:
-PVC sizing is not as consistent as I initially thought. I had to adjust the scaling percentage slightly depending on the batch of PVC.
-PVC is not perfectly round. I found that every piece of PVC is slightly oval, creating asymmetric hot spots on the plunger.
-If you buy several springs, they will not create equal projectile launches.
-if you do not glue the printed parts to the PVC well enough, the launcher will disassemble itself during launch.
-securing the launcher in place is tricky, so I included a bracket that should effectively clamp the launcher to another surface with a nut and bolt.
Overall, my school was able to buy a cheap 3d printer (monoprice mp select mini) and print a dozen of these launchers for less than the cost of one traditional projectile launcher. The printed launchers do not shoot as well, but they are still quite accurate.
I have successfully printed this on the following machines:
Makerbot replicator (.3mm height with raft, no support)
Makerbot replicator + (.3mm height with raft, no support)
Monoprice MP select mini (.175mm height, no raft, no support)
Each machine I had to run a test print first, then adjust the scaling percentage slightly to fit the PVC I had on hand.
Make sure the Plunger (file 1) slides smoothly inside the PVC. Adjust with sandpaper if necessary, or reprint slightly resized.
Use any high strength super glue to permanently bond the launcher post to the plunger. This assembly should then be placed inside the PVC with the spring. Finally, use the glue to permanently bond the end caps onto the PVC.