3D renderThe Pocket Planetary · 3D render of the actual model, two-colour version; the files are the one-colour engraved version. Colours are illustrative.
Pocket Planetary 4:1
A palm-sized gearbox you turn by hand. Four turns of the knob turn the dial once, the same way round. Seven printed pieces, no hardware.
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Our first unit is printed in PLA and working (one print so far). The figures below come from the CAD model and slicer estimates unless marked; we have not measured the fit details (snap, knob, smoothness) yet. Desk toy for ages 14 and up; small parts.
Planets around a sun.
Inside, three small gears roll around a gear in the middle, like planets around a sun, inside a ring of teeth. The knob turns the middle gear.
The dial holds the three planets, so it is carried round with them, slower than the knob. Four turns of the knob take the dial round once, in the same direction.
It is the same kind of gearbox that sits inside cordless drills and robot joints: small, and it trades speed for strength.
Curious how the wobbling-disc kind works? Try the interactive cycloidal drive.
What we know so far.
From the CAD model and Bambu Studio estimates, October 2026. The last row is from our first print.
| Spec | Value | Source |
|---|---|---|
| Ratio | 4:1, same direction | CAD motion study: one knob turn moves the dial 90° |
| Size | Ø57 × 21 mm | Assembled, from the CAD |
| Parts | 7 printed pieces, 0 bought | Five different parts; the planet gear is printed three times |
| Gaps between teeth | About 0.14 to 0.18 mm | 2-D check of all three planets at 53 positions: no overlap |
| Filament | About 24 g, PLA or PETG | Bambu Studio estimate (sliced in PETG); our first unit is PLA |
| Print time | About 2 h 30 min | Bambu Studio estimate, A1 0.4 mm, one part per plate |
| Marks | Engraved, one colour | The HW logo, ticks and arrows are cut 0.6 mm in, so they always show. Our photos show a two-colour unit; same parts |
| Physically tested | First unit printed in PLA and working | One print so far, 57.25 mm across (caliper); we publish fit notes next |
Four steps, no tools.
The file pack includes an illustrated print and assembly guide.
1. Sun gear onto the pivot · 3D render 
2. Three planets in · 3D render 
3. Snap the dial in · 3D render 
4. Press the knob on · 3D render
When can I get it?
The print files are available now: buy them on this page and download straight away. Printed, assembled units come later. Follow @harryson.stl for that launch.
Files or a printed one?
Both are planned: a digital file pack for your own printer (available now), and a printed, assembled one for your desk (later).
Do I need any hardware?
No. Seven printed pieces: the dial snaps in and the knob presses on.
Which filament?
PLA or PETG. Our first unit is printed in PLA and works; PETG flexes a little more for the snap rim.
How is it different from the Pocket Cycloid?
Same size and the same snap-together build, but a different trick inside: the Pocket Cycloid needs 10 turns and goes the other way; this one needs 4 and goes the same way. Both are coming together as the Pocket Gearbox Duo.
Is it a toy for kids?
No. It is a desk toy for ages 14 and up and has small parts.
Want both pocket gearboxes?
The Pocket Planetary and the Pocket Cycloid are coming together in one box.