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.