November 30, 2019
Description
This sphere has a peculiar property: if you toss it in the air it is nearly impossible to spin it around the axis connecting both sides.
The physical phenomenon is called the "tennis racket instability" and the mass distribution inside the wigglyball is chosen to maximize its effect.
I recommend printing the two halves of each wigglyball in different colors, though if you are using a multicolor printer this makes a nice "waste object": the filament that must be purged after each color change is used to construct this object and this produces stripes that illustrate the tumbling nicely.
Printer Brand: Prusa
Printer: i3 MK3 MMU 2
Rafts: No
Supports: Yes
Resolution: 15 mm
Infill: 100%
Filament: generic PLA any
Notes:
To achieve the right mass distribution this object should be printed solid, with 100% infill. It prints as two hemispherical pieces, which should be pinned together with short pieces of 1.75 mm filament and glued. The outside should probably be sanded so that the object handles better. Supports are necessary for the tops of the hemispheres, but the region supported is on the inside, so remnants of the support have no effect on the visible surface. The internal shape does result in a few unintended bumps on the thin outer shell but these can be made inoffensive with sanding.
I have included a Jupyter notebook in which I do some calculations to determine the wiggliest wigglyball. The actual object is modeled in OpenSCAD.
License:
Creative Commons — Attribution
peridot
