This concept for a pearl millet thresher came about as we analyzed the forces and impulses involved in flicking millet seeds off its panicle. Bike spokes are hard steel, with diameter of the order of the size of millet seed, and travel at a high speed near the rim: velocity = 2 * pi * omega (rpm) * r, where r is the radius ~25"/2 (near the rim) and omega is about 60 rpm at the pedal times the gear ratio, say 48 teeth in the front / 14 teeth in the rear ~10 meters/sec (0.01 km/sec * 3600 sec/hr = ~25 mph).

Easy enough to try, we (carefully) held up a pearl millet panicle to a spinning bike spoke, and indeed it cleanly knocked off the seed, on one side, with no apparent damage to seed and little damage to the florets and panicle.

The main challenge for this concept are coming up with an ergonomic, safe design that efficiently collects the seeds.


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