The Bandalore: A Yo-Yo With a Flywheel Rim

US 59,745 shows two similar circular disks A and B, each with "a marginal rim or swell" C on its outside and a central hole D. On the inner side of each, round the hole, is an indented annular boss E; the indentations of one fit the projections of the other, so the two "interlock firmly together on the principle of a clutch" when a rivet F is put through and clenched. A small hole G next to the boss anchors the string H. The patent claims only the construction — the two disks joined by the rivet and interlocking bosses — but names the reason: the rim "exercises the function of a fly-wheel". The drawing sheet itself is headed "Whirligig", and shows a hand letting the toy fall on its string.

3D-print two pairs of disks 56 mm across with a 6 mm axle between them: one pair solid and flat, the other with most of the plastic in a thick outer rim and a thin web. Weigh them and add steel washers to the lighter so both have the same mass. Tie 80 cm of cotton string to each axle and wind it on. Drop both from the same height at the same moment: the rim-weighted one falls more slowly. Time the drops with a stopwatch, and film them if you can, and compare with the notebook. Then try a loop instead of a knot on the axle, and see which one 'sleeps' longer at the bottom.

Toys of this kind are very old; in English they were called bandalores or quizzes by the eighteenth century. **James L. Haven** and **Charles Hettrick** of Cincinnati patented their metal bandalore as **US 59,745** on 20 November 1866. The name yo-yo and the loose-looped 'sleeping' string became popular in the United States in the late 1920s. **Honest limits.** The notebook assumes a rigid string and no slip or friction; real yo-yos lose energy in the string and at the axle, so they never climb all the way back.