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This video shows a prototype 3D printed "vertical ball launcher" printed in ABS plastic on an UP! 3D printer. It is designed such that when you push down on one side of a lever, a piston on the other side moves up and comes into contact with a ping pong ball, which is then launched into the air.

This was designed with the intention of working 3D printing, CAD and engineering design into a middle school science unit on force and motion with a very introduction-level, qualitative approach to topics like position, velocity, acceleration, gravity etc. At the basic level, the device provides a fun introduction to 3D printing for students and a cool way to launch a ball into the air (and then track its trajectory using a camera), instead of just throwing or dropping the ball. At a more advanced level, students who have been introduced to CAD can modify the source files to try and improve performance - for example, changing the lengths of the levers or the geometry of the piston section. Students can also experiment with different methods for driving the lever - for example, a rubber band or a solenoid connected to one end, or a motor driving the central shaft.

Note how using "puzzle piece" style connectors allows you to print much larger objects than would fit on the print tray in a single run (the UP! has a print volume of roughly 12x12x12cm). The design could be modified to laser-cut and snap/glue together the majority of the structure instead of 3D printing, especially the truss-like supports. With a little ingenuity you could probably laser cut the entire thing, although this would be more difficult for the round parts.

STL files can be downloaded from Thingiverse: http://www.thingiverse.com/thing:98130.

Tips for 3D printing:
  • Cylindrical surfaces will generally come out the highest quality if they are printed with their axis oriented vertically.
  • Some of the larger parts take a while to print on the UP (8+ hours) so it may be easier to start a print job before you to go bed and let it run overnight.
  • You can put more than one part on a print tray at a time, just make sure they aren't overlapping.
  • Note that you will need two of the "pin.stl" part, two "side.stl" parts and one of everything else.
  • I can't guarantee that the tolerances for the snap-together parts will be perfect - this could vary on different printers. If your parts are too big to fit together, you can sand them down or shave off some plastic with a hobby knife. If they're too small and wiggle a bit, you can use glue to secure connections.
  • I printed this on an UP! since I had access to one, but it should work on other similar consumer-grade printers like the Makerbot or Cube (no guarantees though).

This is more of an open-ended design challenge than a step-by-step Instructable. If you're used to 3D printing singular solid objects, this could be a good introduction to printing functional devices with interlocking, moving parts. If you're just looking for a fun physics or engineering challenge (for yourself, your kids or your students), then there is plenty of room for improvement in this design. Either way, have fun - and if you wind up making your own, be sure to post links to pictures and/or videos in the comments section!

Credits: this ball launcher was designed at the Cornell Creative Machines Lab in collaboration with the Curry School of Educationat the University of Virginia.
Coooool!!
Just made mine!!!! Works great!
Cool! Are you using this in a classroom setting or just for fun?
Did you print every piece seperately? <br>
Yes, each piece is printed separately and then assembled, but you can still fit multiple parts onto a single print tray (they just have to print separately, not interlocked). On an industrial printer with support material you could just print the whole thing all at once.
nice mechanism

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Bio: For my day job I write K-12 STEM projects for www.sciencebuddies.org. In my spare time I write Instructables.
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