Applied Physics students Sam Hewitt and Luis Contreras helped build a prototype bike thresher demonstrating two innovations in the bike support and the threshing wheel.


Our stand proved surprisingly stable (we didn't even lock the handlebars), offers easy height adjustment for ergonomics, requires no modification of the bike frame, and is simple and cheap. It is constructed from two ~30" lengths of 3/4" EMT conduit with a ~30 degree bend ~16" from an end (note, none of these dimensions were measured). Four hose clamps attach the EMT tubes to the bike frame.





Our wheel had an aluminum rim, which we found cracked when we tried to bend the sides flat enough to access the millet to the spoke heads. Instead we purchased a strip of construction wire used to cover wall corners so drywall mud will adhere ($4/10' at Home Depot, but just about any wire mesh should do). We bent the wire loosely around the rim, tying it periodically between the spokes, and pressed the top with conduit to create a flat to concave threshing surface.


(Note the remaining piece of wire mesh is on the ground in the background).



The result was a pretty ugly wheel (and there was much skepticism that this would work). Also note the mesh is not horizontal/vertical, but diagonal, yet it doesn't matter. The threshing process is quite robust. We have little millet to test, but it stripped grain completely without stripping florets, from a couple of old and very dry panicles. This prototype throws grain fairly widely and we made no attempt to collect the grain, but will use the prototype for high speed photography of the threshing process.

It's hard to gauge the performance of this thresher relative to that of spoke nuts or the sides of the spokes. I suspect its performance is more efficient than spoke nuts because the wire characteristics interface with the millet better, yet it throws grain less widely than threshing in the spokes themselves.



Note that a tire could remain on the wheel below the wire. So a user could conceivably ride the bike to the field carrying the support tubes, hose clamps, wire wheel cover, and a reversible fender (which we haven't made -- as it will interfere with photography), and convert their bike to a thresher relatively easily.


The result, without rotating the stalk (I'm conserving my few precious stalks), is excellent.