1. Mick West

    Mick West Administrator Staff Member

    We are all familiar with the classic example of a weak thing breaking a strong thing - the ping-pong ball being shot through a ping-pong paddle at very high speeds.
    ping-pong-ball-going-through-a-paddle-this-is-at-frames-per-second-118849.
    Source video here.

    This is useful (to a degree) for illustrating things like how aluminum planes can break though the steel and glass facade of a building.

    But I was wondering if the same thing might be possible with my favorite stand-in object: the aluminum soda can.

    I've done a couple of very preliminary experiments using bungee cords and a "sled" with a can on it.

    Metabunk 2018-05-22 15-19-51.
    Two bungie cords to launch it. One to slow it down (allowing the can to continue ), and a "trigger" of a cable tie.
    Metabunk 2018-05-22 15-20-56.

    Result is a high speed soda can that hits a target at failrt high speed.
    IMG_2692a.
    Calculating from the video, it goes at about 2/5 its length in 1/240th of a second, so 2/5*.12/(1/240) = 11.5 m/s or 25 mph.

    This, of course, is not very fast. The "slow" version of the compressed air ping-pong ball gun goes at 400 mph.

    I'm not sure if I'll proceed much more with this, as it would get dangerous fairly quickly. But I though I'd ask for suggestions. Is a vacuum tube the only way to go?
     
  2. Hevach

    Hevach Senior Member

    Best affordable (for sufficiently expensive definitions of affordable, you could probably do something for under $200 if you wait for Harbor Freight to have a parking lot sale) setup I could imagine would be with a compressor.

    The fastest way to get all of the air out of a compressor I figured out trying to make an air cannon (with some success) in college was to replace the drain cock at the bottom with a ball valve, run the compressor until it shuts off and open the ball valve, it'll decompress much faster without a regulator or other hardware. In our attempt, we ended up drilling a new hole in the compressor tank (I've since learned this was an epically bad idea!) and added a 1/2" ball valve (deciding the 3/8" valve on the drain cock outlet wasn't irresponsible enough already), running a hose from that to a 1/4" PVC pipe and fired marbles into a brick wall. The brick chipped a couple times, and the marbles exploded into an incredibly fine glass dust.

    This way you get acceleration all along the pipe, bungee cords will deliver less and less tension as they contract, in the image you can see they've already gone limp and the can is just coasting on momentum already.
     
    • Informative Informative x 1
    • Useful Useful x 1
  3. Mick West

    Mick West Administrator Staff Member

    Hmm, I would not have thought a vacuum cleaner would have enough suck. Interesting.

    Soda can is 2.6" inches across. In theory some nominal 2.5" PVC pipes are just over 2.6" Inner Diameter (ID), like Class 200 2.5". Maybe time to visit Home Depot.
     
  4. Last edited: May 23, 2018
    • Useful Useful x 1
  5. why not use a slim/sleek can, like those for energy-drinks? they usually have a diameter of around 2". would help to keep the diameter for the pipe as small as possible.

    and another thought; would be messy for sure, but instead of a foam-layer for max efficiency to seal the possible gap between pipe and can maybe just oil or some sort of grease/fat? hm, maybe not so good for the vacuumcleaner...
     
    Last edited: May 23, 2018
    • Like Like x 1
  6. Mick West

    Mick West Administrator Staff Member

    Because I have a free supply of empty diet coke cans and those energy drinks are expensive!
    Also the smaller cans seem to have stronger walls, with the smaller diameter.
     
    • Like Like x 1
    • Funny Funny x 1
  7. :D
     
  8. DeBean

    DeBean New Member

    Have you considered a propane or aerosol based launcher ?

    There are many designs for hand held launchers on the web (not recommended) however, depending on how you build the rig I think it could be quite safe (or at least as safe as bungee cord). I would recommend you go to an uninhabited area for testing.
    I would first create a safe area protected by a large mass as a control point and I would don personal protective equipment. Pin the launcher to the ground and then cover with sandbags. Remotely inject gas and then disconnect before using a piezo ignition system to ignite. It would be a fun way to reduce volume when recycling.
     
  9. Mick West

    Mick West Administrator Staff Member

    That does sound like fun. A problem in these parts is the super high fire risk, which has put a stop to my thermite experiments. I do have some space out back to experiment, but I think I shall wait until the fire risk has passed before I mess with flammable gasses (or really anything high energy).