Brain Puzzle

A few weeks back, I saw a great video from Maker’s Muse on YouTube, describing how to make custom 3×3 puzzles (eg. a Rubik’s cube) out of any 3 dimensional model. I’ve always been curious about how these puzzles work, so what batter way to learn than to make my own?

Final puzzle. 3D printed and painted.

Yup. It’s a brain.

From brain scan to brain surgery

I started with this brain model from Thingiverse. These puzzles work best when there is good symmetry across X/Y/Z axes, so I scaled the model asymmetrically to improve its overall symmetry.

Scaled brain with deep folds and crevices.

I had to create a solid “core” for the model, because there is a large gap between lobes and several deep folds that would have made it impossible to divide the model into contiguous puzzle pieces. To create this core, I used MeshLab to create a “bubble shell“.

The bubble shell core.
Original model with bubble shell core.

Next, I took the union of the scaled model and core, then took the boolean difference with the 3×3 puzzle template from Maker’s Muse.

Model after boolean difference with Maker’s Muse 3v3 template applied. Each puzzle piece has chamfered edges to improve movement.

Models generated from 3d scans are often really messy and if they aren’t repaired, mesh operations fail. When I have problems with bad meshes, I often turn to Netfabb to repair the meshes and move on. It turned out that Netfabb’s “standard” repair operations weren’t good enough for this model. I had to use the full version for “extended” repair. I also used Netfabb for all of the boolean operations.

Final model with painted folds. This model would be very hard to solve if it monochrome.

When the modelling was finished, I printed all of the parts on a Prusa i3 Mk3 (about 24 hours of print time for one puzzle). I then sanded and primed the unassembled parts. I assembled the puzzle with springs and M3 screws. Finally, I painted the interior of the folds on each “side” with acrylic paint.

Final puzzle. Printed and painted.
Interior view of model. Pieces are centers, edges, or corners. Centers connect to a 6-side core (not pictured) with screws and springs.

Learnings

  • It was great to get hands-on to really see how these puzzles work. It’s a very clever design. I really recommend this Maker’s Muse video to see more details on the mechanics.
  • The movement on this puzzle is good (not great). It particularly helps to apply silicone lubricant periodically.
  • This puzzle is a little harder than a 3×3 cube. Since there isn’t symmetry in the center pieces, their orientation matters.
Well, this is embarrassing. Somehow, this is the only photo I have of the puzzle unsolved.

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