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Viable Railgun Setup? (ping pong balls)

  1. Dec 31, 2014 #1

    I'm working on a personal project that requires a very precise, but not very powerful, ping pong ball launcher. Would it be possible to coat a ball in metallic conductive paint, and then fire it from two rails like a railgun? Would I still get a constant net force in the correct direction if the electric current is running all across the surface of the ball? Thanks for your help.
  2. jcsd
  3. Dec 31, 2014 #2


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    Staff: Mentor

    I guess it is possible, but variable conductivity across the surface and a variable contact to the rails could be an issue for the precision. In addition, railguns need very high currents, that leads to other issues.
    A while ago, I made a mechanical system with an electromagnet and a spring. Worked quite well with a very improvised setup.
  4. Dec 31, 2014 #3

    Doug Huffman

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    It is not viable for the required current density in the ball film, with sufficient metal it stops being a film or even a ping pong ball.
  5. Dec 31, 2014 #4
    I see. Thanks for the explanation. And thank you for the suggestion, but my project is a bit tricky, as I need to create a fast and fluid controlled cycle of feeding consecutive balls down and then launching them up and back to the starting point (into a bowl-like reservoir). I'd initially tested out a motorized wheel launcher with a servo feeder, but that launch mechanism turned out not to be precise enough.
  6. Jan 1, 2015 #5
    What aspect of your current design is insufficiently accurate? Is it the loading? Power? Direction?
  7. Jan 1, 2015 #6
    I think it's a combination of all of them, because my objective is to have the ball consistently land on the same point (plus/minus a few millimeters) after each launch, which did not even come close. I've considered some possible causes, like the track being 3D-printed (resulting in a "step-like" sloped surface), and maybe also the unpredictability of how the fast-spinning wheel grips the initially slow-moving ball when they come into contact. So I'm thinking about remaking a prototype with a copper-wire track, and I'm going to experiment some more with the wheel-launcher setup.

    By the way, I know my descriptions only give a vague idea of my project, so this video starting at the 1:00 timepoint should make everything clear (those of you familiar with Animusic will recognize it). My goal is to recreate a real-life version of this CGI xylophone fountain:
  8. Jan 1, 2015 #7
    Are you aiming to hit multiple targets as shown in the video (the xylophone bars) or your simpler written description of launching a ping pong ball from a fixed launcher to a fixed target every time?

    If you have a photo or a diagram of what you currently have that would be also be useful. If you don't have one already a barrel may improve the accuracy.
  9. Jan 1, 2015 #8
    My plan is to have a set of parts (balls, launcher, feeder, etc.) for each separate note, and ultimately coordinate all the ball feeders with an arduino. That way I don't have to worry about the timing involved in a moving ball launcher like the one used in Intel's model of the xylophone fountain. So my first step is to create a working prototype for a single xylophone bar, and afterward just replicate the same system for each note of the whole instrument.

    And I opted for just a pair of rails instead of a barrel because I think with a barrel I would need to find an impossibly perfect diameter that will not be narrow enough to slow the ball with friction and yet also will also not be wide enough to allow small random bouncing to reduce the precision/consistency of the trajectory.
  10. Jan 1, 2015 #9
    Having separate launchers definitely simplifies the aiming.

    Is there not a risk that the ping pong ball would bounce against the rails as well? If anything it may be a bigger issue as the ball can travel further from the two rails. The barrel doesn't need to be anything special - a rolled up sheet of paper may work.

    How does your wheel connect with the ball?
  11. Jan 1, 2015 #10
    Having the ball bouncing against the rails hasn't been a problem, because I accelerate the ball at the bottom of the slope just before it reaches the curved rails (imagine a capital letter "J" tilted ~60 degrees clockwise; the ball rolls down the straight part, and then gets accelerated forward right before reaching the curved part), so I believe the momentum of the ball keeps it pressed against the rails up until the moment it flies into the air.

    In my 3D-printed model, I have the wheel positioned in the air above the bottom of the incline and constantly spinning. So as the ball rolls down the incline, when it comes into contact with the wheel, the ball gets accelerated forward up the curved rails and into the air, upwards and slightly backwards (since the xylophone bar is positions directly above the incline).
  12. Jan 1, 2015 #11
    Sounds like a decent approach.

    Not sure what to suggest for further modifications. Perhaps video the device in operation and track the ball to see where the inaccuracies start appearing?
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