Bigfoot (Triggered Ball Valve Cannon)

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Posts: 145
Joined: Sun Jan 20, 2008 12:01 pm

Thu Nov 03, 2016 8:02 pm

Hi Potato Launching Connoisseurs!

This is my latest cannon which is a simple ball valve pneumatic launcher. The most notable features are the ABS DWV pipe construction and the spring loaded triggering mechanism.



So let's talk about the ABS. I think it is safe to use as long as I stay away from certain fittings like ones with threads or sharp internal corners. For the end cap I used a bushing instead of an end cap because I think it is more durable. If I used a 4" cap, the corners would be put under a lot of concentrated stress and could experience fatigue failure. The attachment to the ball valve is a bit special. Because I didn't want to use ABS threaded fittings because they are weak (from my experience and observation), I made a more robust fastening method. I filed out the stop inside the 2" female hole of the 4" bushing. Then I glued in a 2" SCH80 PVC nipple all the way through with threads sticking out the back end. I also glued a ring of 2" coupler to the PVC nipple to act as a stopper. Then I used a 2" PVC female threaded coupler as a locknut on the interior side of the bushing. I used glue made for both ABS and PVC for this bond. I also reinforced the 4" ABS barrel-end bushing with small rectangles of flattened ABS and glued them in there with ABS cement. I hydrotested the chamber to 100psi and held it there for 5 minutes. Not leaks or visible failure!

Okay now for the triggering mechanism! It is powered using rubber exercise bands. The housing is 1.5" ABS pipe. the piston is a 1" PVC end cap. The bands and paracord are secured at each end with eye screws. The trigger latch is made from 3 layers of flattened 1" PVC pipe glued together. The trigger pivot bracket is made from ABS pipe cut and formed using a heat gun and pieces of wood. The pulley guide is made from a screen door replacement wheel. The bracket is also made from ABS pipe formed with a heat gun and glued to the 1.5" end cap using ABS cement.The whole assembly is mounted to the cannon at the 4" coupling and cemented on using 14 ABS brackets that match the curvature of the trigger device and chamber. That took a lot of filing!


The opening time of the ball valve is at maximum 80 milliseconds based on the footage below.

In the shooting video, I was able to punch through 3/4" plywood when loaded with a potato and pressurized to 90psi. I just found the wood laying there and I was a little wet, but otherwise quite strong.
If you are confused by my explanation of the triggering mechanism or the bushing reinforcement let me know and I can make a diagram if that helps. Thanks for reading!