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01 · Rotational fidget mechanism · printed and fit-tuned

Tri-Spin

A three-armed rotor on a fixed axle, with weighted ends that keep it turning.

The first thing I ever wanted to fix was the spinner in my pocket: the bearing rattled and the arms were too light to keep going. Tri-Spin is my answer to a simple question, how little do you need to make a satisfying spin?

Download my files How it works

01The mechanism

How it works.

What this one taught me: Mass distribution, bearing clearance, and why a 0.2 mm change in a printed hole decides whether a part spins or seizes.

A fixed base carries a central axle. A rotating hub sits on the axle, and three equally spaced arms leave the hub and end in weighted circular pads.

A bearing race surrounds the hub and forms part of the rotating assembly. When the rotor is flicked, all three arms turn together around the axle; the weighted ends move mass away from the centre and keep the rotation going.

The design concentrates on one repeatable tactile interaction: a spin that is easy to start, easy to feel and easy to stop.

02Parts

Every part, named.

Dimensions are from my STL files. Parts without a file are printed as part of a neighbour or are plain primitives in the model.

  • Rotor bodyHub, three arms and weighted pads printed as one pieceSTL
  • Axle12 mm fixed axle, press-fit into the baseSTL
  • Bearing washerThe race the hub rides onSTL
  • Retaining washerKeeps the rotor on the axleSTL
  • BaseAny flat disc; a 40 mm cylinder is used in the modelNo file

03Files

Print it yourself.

Shared under CC BY 4.0. My Python script rebuilds the assembly in Blender 3.6 or later from primitives and animates it; the STL parts are the printable components and may need fit tuning for your printer.

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Printed one? Tell me.

If you print one of my designs, or change one, send me a photo. Remixes are the point.

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