Science World Vacuum Cannon project photos

I’d like to share some photos of a project I recently completed at work that I’m particularly proud of.

This is a ping pong ball vacuum cannon that I was asked to build for Science World’s On the Road team that travels to schools across the province to perform science demonstrations. It can launch a ping pong ball at over 1000km/h, measured by an infrared ballistic chronometer that I built specifically for this. This vacuum cannon is the 2nd version of one that I built a few years ago, and is built inside of a Pelican 1720 rifle case for portability and a high-tech/sci-fi appearance

All of the work was done myself in the Science World exhibits workshop. The black plastic panels were designed in SolidWorks and then Laser-cut out of 1/4" ABS (SW’s laser cutter has some really powerful exhaust ventilation – ABS is a banned material in the VHS laser cutter, and in the future I’d probably send the ABS out for water jet cutting instead since the laser leaves a sooty edge), and I used transparent blue acrylic to cover the LED displays.

I built the electronics onto protoboard. The speed displays are made of giant 7 segment displays each driven by a TPIC6B595 power shift register chip. I wrote my own library to parse a floating point number onto the seven segment displays. The unit displays are Adafruit 8x8 neomatrix modules. The speed is measured by two infrared phototransistors spaced 10cm apart in a 3D printed housing that snaps onto the cannon. The whole thing is controlled by a Teensy LC microcontroller board, and the speed measurement uses hardware interrupts for accuracy.

The hardest part of this project was understanding all of the different material properties. For example, the Pelican case is made of polypropylene, which I had lots of difficulty finding an adhesive that worked (I found a specific type of 3M VHB tape that works on Low Surface Energy plastics like polypropylene.). There was also learning how to TIG weld aluminum.

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Really lovely build, @JohnC!

The blue on black gives it a really modern and professional look.

The hardest part of this project was understanding all of the different material properties.

Sounds like a lot of valuable knowledge came out of discovering the material interactions, and I’d love to hear more about what you learned.

Thank you for sharing!

I wish I’d known you were trying to bond LSE plastics. I have Loctite 3035 which will bond UHMW. Works very well.

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1000km/h? i wouldnt want to return that serve

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What did you use for the seals/how did you solve the seals being broken/re-applied?

The seals are pieces of mylar film/emergency blanket stretched over the ends of the PVC pipe and held in place by PVC pipe couplings slipped over the ends

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We built one at protospace, but not nearly as nice. I can tell you that a ~300km/pingpong ball hitting a paddle 1 foot away from the muzzle leaves a nice round hole in the paddle, loony toons style. The speed drops off remarkably quickly with distance due to air resistance and low mass.

edit - also ferro roches are remarkably close in diameter to a ping pong ball, and come with their own sabot. They turn ino pancakes when fired at an anvil.

We used tuck tape as our burst discs (that red tape you apply to vapour barrier and broken taillights). Worked pretty well, just for the love of cuthulu dont stand in line with either end in case it pops early.

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