Solar Powered Dancing Duck

A small solar cell doesn’t get much power with indoor lighting. As far as consumer electronics go, I haven’t seen much beyond a solar-powered desktop calculator. I had thought there’d never be enough power for an indoor solar mechanical device, but a few years back little solar-powered pendulum toys started showing up. I usually see them as little waving cats (maneki-neko) like the teardown and analysis posted to Hackaday.

This device is a variation of the same basic idea. Instead of waving a cat’s arm, the pendulum swings the body. An additional sophistication in this design is a second linkage that swings the head in the opposite direction of the body, creating a dancing duck. It was purchased for a buck and a half from Daiso Japan, so we’re looking at something produced for raw material cost somewhere a quarter (if even that much.) It was an impulse buy and wasn’t expected to last very long, but it actually ran for years before suffering mechanical issues and frequently getting stuck. It was then moved to a window ledge, where it could occasionally swing its head and hips under power of direct sunlight. But the sun that gave it a second life also took away its shine: brightly colored plastic started fading rapidly and became brittle. Finally, an unfortunate fall from that window ledge ended this duck’s performance career.

Poor duck broke its neck in the fall. The neck linkage was lost, but we can see the head’s pivot point inside the neck, where plastic shaded from direct sun is a visibly more vibrant shade of yellow.

I think the bottom of the base was originally glued in place, but that glue has weakened with age (or sun) and could be easily pried apart.

A small solar cell feeds into a circuit board, home to just two components: an electrolytic capacitor and a chip under a blob of epoxy. A coil wound from super fine copper wires is attached to this board as well. As explained in the Hackaday link above, this coil is both input and output: for sensing position of the magnet and for creating a magnetic field to boost the magnet’s swing.

The coil looked off-center, so I broke off the rear side of the base and reinstalled it to verify the coil is indeed off center when the magnetic pendulum (black plastic with black magnet on the bottom) is at rest. There is only about a millimeter of air between the coil and the magnet, a much closer distance than found in the cat mentioned in the Hackaday post.

This old dancing duck has a bit of arthritis and could not self-start under indoor light. I gave the pendulum a small tap and it started rocking but halted again after a few seconds. We can see the problem in the pivot point, which was designed to minimize friction. The pendulum axle has a triangular profile, so only a tiny sharp point touches the circular hole in the base. Years of dancing in the sun has worn both components. The triangular wedge’s sharp edge has been rounded off, and the hole perimeter is no longer circular. Together these two parts presented too much friction for the pendulum to overcome.

Daiso has long since stopped carrying this device, and I had no luck finding an exact replacement. There is no shortage of solar-powered dancing ducks for sale, but they all looked different from this cute little thing. Some are the opposite of cute, and a few looked downright scary! I have to say goodbye to this dancing duck now, it gave its all for dance and was quite an entertaining $1.50 spent.

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