Customizable Geneva Drive Desktop Model - 4, 6, 8 Slot Presets with Hand Crank (Educational)

CUSTOMIZABLE educational model: a hand-cranked Geneva drive you can rebuild in the free TrueGeometry Playground with 4, 6 or 8 slots. Turn the crank and the slotted star wheel advances one slot per turn, then locks and rests. Made for students and teachers to print, turn by hand and study intermittent motion. The included STLs are the three presets (wheel 80 mm, pin 6 mm).

UNTESTED DESIGN STUDY - please read first. This model has not been printed or test-fitted. Clearance was checked by hand calculation plus a numeric sweep of the crank every 0.5 degrees over a full turn (minimum pin-to-star gap 0.40 to 0.50 mm, no overlap). It was not checked with a physical print, and printer tolerance can use up that gap, so test-fit and sand the slot and pin. The star tips on the 6 and 8 slot presets are knife-edge and fragile; start with the 4 slot preset. The parts are separate overlapping shells, not unioned, so check or repair the mesh in your slicer. Scale, orientation, supports and material are your decisions.

What you get: driver wheel with pin, slotted star wheel, lock disc, back plate and plinth, and a crank arm with a front handle and knob (the hand crank).

Presets (slots, crank radius, centre distance): 4 slots 35.5 mm / 50.2 mm, 6 slots 20.5 mm / 41.0 mm, 8 slots 14.7 mm / 38.4 mm.

Files:

1. geneva-drive-4slot.stl - 4 slot preset (main file), 145.7 x 106 x 64 mm, Y up, 5,456 triangles, closed mesh.

2. geneva-drive-6slot.stl - 6 slot preset, 126 x 106 x 64 mm, 5,268 triangles, closed mesh.

3. geneva-drive-8slot.stl - 8 slot preset, 123.4 x 106 x 64 mm, 5,260 triangles, closed mesh.

4. geneva-drive-recipes.txt - the full Playground command recipes for all three presets.

5. geneva-drive-playground-guide.pdf - how to run and customize the recipe, with the Script panel screenshot.

How to customize: open the Playground, paste the recipe chunks one at a time with Script and Run, and pick the 4, 6 or 8 slot recipe. The slot count, wheel diameter and pin diameter are listed at the top of each recipe. Wheel and pin diameter are changed by regenerating the star and lock disc coordinate lists with the formulas in the guide; they are not live sliders. Step-by-step article with FAQs and tables, including the full recipe: https://blog.truegeometry.com/0_0_0_0/blogs/post-4bf9b272.html

Classroom ideas: count the stops per crank turn, compare 4, 6 and 8 slots, and compare how long the star rests with how long it moves.

If you print one, please post a Make and tell us how the crank and star run.

Built with native Playground commands only: no external scripts and no boolean cuts. AI-assisted design. License CC BY-NC 4.0: share and adapt with credit to TrueGeometry for non-commercial and educational use. Commercial use requires consent from TrueGeometry.

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