POWER PRODUCTION AND TRANSMISSION DESIGN ADOPTED
The power production and transmission parts are integral with the thresher (rightly or wrongly!). 4 pedallers sit upright in rectangular layout, pedalling 2 crankshafts located in 4 ball bearings. Each crankshaft has a 44 tooth sprocket which drives its own 18 tooth sprocket on the layshaft, which runs in 2 ball bearings. These sprockets are standard bicycle units. A 44 tooth sprocket on the other end of the layshaft then drives via a bicycle chain to the 18 tooth sprocket on the thresher shaft.
Each pedaller sits in conventional bicycle fashion on a wooden or sprung leather saddle on a height-adjustable pillar, gripping 'handlebars' which are height-adjustable on 4 slanting pillars. The outer pedals can be of conventional bicycle type (or can be wooden pedals), but the inner 'pedals' are of split polyethylene tubing, within which the 25mm diameter pedal spindles rotate.
Note that many variations of this design are possible - with varying mechanical efficiency advantages, wear reduction advantages, and cost disadvantages.
The whole machine is supported on 3 short legs, and the largely 2-dimensional layout simplifies production by facilitating before and while electric arc welding of the frame takes place. All bearing housings have generous slots which facilitate sprocket alignment and chain tensioning. Incidentally, to ensure correct bearing alignment for the 2 crankshafts, the following procedure should be observed: complete all lathe operations on the crankshaft, then weld on the 2 inner cranks and the inner pedal spindles; only after cooling should the redundant section of the crankshaft be cut out by means of a hacksaw or power hacksaw.
The 2 outer 'left-hand' cranks (which are in fact driven by the right feet of 2 of the pedallers) and the 2 outer 'right-hand' cranks and chainwheels can be driven on to their respective shafts, lined up, and lightly welded in place. Alternatively, flats may be produced beforehand, by skilled workmen using steel rule, hacksaw and flat file, for the fitting of standard bicycle cotter-pins. Or the flats can be produced by milling machine or lathe with milling attachment if available. The light welding option is probably the lowest cost method, and dismantling can be done using a portable angle grinder on the welds. Quite honestly we havent really thought through all the possibly required onsite maintenance and repair operations which may be required.
Similarly, to prevent theft, the bicycle pedal spindles can be 'spot' arc welded to their respective cranks.
Incidentally, costs can be reduced by changing the 4 conventional bicycle pedals to home-made wooden pedals running on lathe-turned mild steel pedal spindles of say 12 mm diameter. With a coefficient of friction of 0.15, then the total additional power loss would be about 3 watts per pedaller - not at all bad. Use wooden pedals with grip slots and which have been soaked or boiled in old engine oil to impregnate them. If possible use African Blackwood, East African Afrormosia or Msaraka as the timber (also known as Dalbergia Melanoxylon, Mpingo, Spirostachys Africana, Muvanga and Afrormosia Angolensis) - see my report on Materials for Wooden Bearings, Lubrication Techniques and Wear Characteristics .
The total machine weight, with wooden beaters, is 115 kg, and overall dimensions are approximately 2.2 metres square x 1.2 metres high.