Capybara Daruma Roly-Poly - Always Gets Back Up (Wish Box, AMS)

The GIF shows the real motion: a full rocking cycle computed from the measured mass, centre of mass and inertia of this exact print (period 0.93 s at ±35°).

A capybara-daruma okiagari-koboshi: the traditional Japanese good-luck roly-poly that always gets back up, turned into a round red-and-gold capybara with a golden yuzu on its head. Push it, tip it to 80°, it rocks back upright every time. The yuzu is a twist-lock lid over a wish chamber: roll up a paper wish or drop in a few coins.

Details

• Size Ø80 × 111 mm (with the yuzu). Spherical base R = 40 mm, printed as an exact sphere so it rolls smoothly.

• 4 AMS colours inlaid flush (0.8 mm): lacquer red, gold, white, black. White face with capybara snout, eyes with highlights, nostrils and whisker dots; gold brows and face outline; gold asanoha medallion; gold seigaiha wave band; gold belt hiding the seam; small black "HANMA" on the back and under the base.

• Counterweight: 15 × M8 hex nuts (DIN 934, 13 mm across flats, ≈5 g each = 75 g) in a honeycomb of 7 pockets (3 in the centre, 2 in each of the 6 around). It already self-rights with 4 nuts; 15 give a big margin.

• Wish chamber Ø24.5 × 35 mm: fits a rolled paper and coins up to 24 mm (1 €, 10 ¥, 100 ¥, 1 ¥). Up to 60 g of coins and it still stands up.

• Yuzu lid: bayonet with 3 lugs, drop in and twist 60° to lock (0.25 mm clearance). Base and body join with a press-fit ring (0.1 mm clearance, add a drop of glue if you like), so you can open it to change the weight.

• 4 parts on one A1 mini plate, no supports (only short flat bridges over the nut pockets). Real slicer numbers (Bambu Studio, 0.2 mm, 10 % infill): 18 h 50 min, 270 g (red 129 + gold 98 + white 33 + black 10); the parts themselves weigh 86 g, the rest is colour-change purge because the gold and white details run through most layers.

Assembly

1. Drop 3 nuts in the centre pocket and 2 in each of the 6 others.

2. Press the ring into the base groove, then press the body on (any rotation works).

3. Put your wish inside, set the yuzu in with a lug in each notch and twist 60°.

How it was checked

• Mass taken layer by layer like the slicer (2 walls, 5 top / 3 bottom layers, 10 % infill), scaled to the slicer grams of each part (body 56.6 g, base 19.3 g, yuzu 6.9 g, ring 2.8 g). With nuts: 161 g, centre of mass 9.2 mm below the centre of curvature. Without nuts it sits 5.0 mm above it: control test, it stays lying down.

• Potential energy computed in 40 000 orientations: exactly 1 minimum, upright. No other resting position, so it cannot roll away and stay lying. Along 72 directions it rises continuously up to 80°, and up to 80° the contact is always on the spherical base.

• Rolling-without-slipping simulation: released at 45° and 80° it passes upright in 238 / 275 ms; friction needed ≤ 0.15; small-swing period 0.89 s. The contact point travels up to 56 mm, so keep it about 6 cm from the table edge.

• Robust to ±15 % plastic and ±10 % nut weight. Nuts, coins, ring and bayonet tested for collisions at every angle, with control tests that must fail (bigger nut, 500 ¥ coin, wider ring, locked lid lifted).

About this design

Designed with AI assistance and checked in code before release (see above). Pictures are 3D renders and the slicer preview, not photos. Not printed yet: makes and feedback are very welcome.

Español

Tentetieso capibara-daruma de la suerte: siempre se levanta (15 tuercas M8 de contrapeso, comprobado hasta 80°). El yuzu de oro es una tapa de bayoneta sobre una cámara para guardar un deseo en papel o monedas. 4 colores AMS, sin soportes.

العربية

دمية يابانية للحظ الجيد على شكل كابيبارا، تنهض دائما مهما أملتها (ثقل موازنة من 15 صامولة M8، مختبرة حتى 80°). ثمرة اليوزو الذهبية غطاء يقفل بالتدوير فوق حجرة لحفظ أمنية مكتوبة أو عملات. أربعة ألوان AMS وبلا دعامات.