THE DYNAPOD / PEDAL POWER UNIT CONCEPT AND VARIOUS DESIGN ALTERNATIVES - some thoughts and overview , tricks and tips (1999)
Action or Mechanism -
Pedalling, treadling or rowing action. Most of my / our work at Morogoro concentrated on pedalling, but at the end we made a really nice 2-man rowing action (trolley) water pump. That was real inexpensive and very effective, and that rowing concept can easily be extended to 4 persons sitting side by side and back to back together (like a Zundap Janus). Even 6 or 8 person designs could be made cheaply. But sliding action is kind of limited to water pumping, and could possibly be extended through 2 pulleys to powering a traditional morter and pestle grain milling unit (if that makes any sense). Sure it could also be hitched to a crank
To give rotary action but then most of the saving and simplicity is gone. Note that for our trolley system the 2 operators themselves are in pretty much constant motion, but that it should be equally possible to make the operators stationary and have only the drive shaft and footrests slide - there may be some advantages in that, e.g. increased efficiency.
Even rowing with a rope and drum and a freewheel mechanism, with or without a spring, might make some sense for some application. The freewheel from a bicycle could be used.
Treadling - we never did of that, but maybe again for 4,6 or more persons that would make some sense, either with treadling from a standing position or seated or semi-seated. Or some pedalling / treadling hibred - say one long crankshaft with throws for 4 - 6 - 8 or more persons, or 2 bearing units with 2 long planks joining the 4 pedals and room for 4 - 6 - 8 or more pedallers in between those 2 bearing units.
Position - all our pedalling designs were conventional upright, but maybe for cost reasons sometimes designs with a reclining pedaller or pedallers might make sense, especially if 2 persons can sit facing reclining and working together on one set of pedals - that saves a lot of chains, bearings, belts steel, wood etc etc.. A very small, compact, light and inexpensive unit could be built around 4 people facing each other pedalling one crankshaft, with a second layshaft running at 2.5 times the speed of this main crankshaft. Each of these 2 shafts could offer chainwheel, 600mm diameter pulley, direct shaft/ flexible coupling drive and possibly the initial crankshaft could offer small sprocket drive also (to enable stepdown to 20 rev/minute). If a flywheel is required for anything it can be fixed onto the direct shaft drive. The more I think about this machine the more excited I get - I probably recommend that such a design supercedes the power generation and transmission configuration as shown in the photos and drawings in this report.... Contact me on firstname.lastname@example.org if you want more details on this idea.
Handlebars - we tended to make home-made copies of conventional cowhorn shape handlebars, usually height adjustable.
Saddles/seating - Wooden or leather sprung or wooden padded. Height adjustable or not
Plastic seating, wooden seating, with or without padding. Wooden padded was probably the best and most cost effective option. Our wooden seats had the 3 fastening and locating holes in the same place as the real thing so that substitution either way could be performed. Wooden saddles were less likely to get stolen.
Pedals - Conventional bicycle or wooden with metal spindle or split plastic pipe.
Solid wooden or split wooden (for easy replacement).
Bearings and Power Transmission
- 4 independent PBUs with wooden bearings
- solid wooden vs split wooden bearings
- crankshaft gang of 2 with roller bearings
- crankshaft gang of 2 with wooden solid or split bearings
Most of our designs used options (1), (3) or (6) above, without problems and with plenty of success. We tended to use solid wooden rather than split wooden since we stupidly did not lay enough emphasis on future serviceability. Our PBUs of types (1) and (3) above were largely interchangeable - by loosening a clamping setscrew on the dynapod frame a PBU could be removed and replaced by another of the same or another type.... By and large wooden bearings were OK for the first stage of transmission at about 60 rev/minute, but not for higher speeds.
Usually these choices are down to the more expensive solution saving some human energy loss or wastage, and often also requiring more sophisticated capital production equipment and/or higher skilled personnel for production and assembly. Choice depends on the economics. If possible of course design with upgrades or downgrades in mind so that the machine can be changed to use the alternatives if and when more (or less) money becomes available and/or when a maintenance activity is required - but that is not often that easy in practice.
Chain, Belt and Shaft Drive
Bicycle chain drive proved very effective for a number of devices. Belt drive was probably required for high speed equipment such as the centrifugal pump (3500 rev/minute) and for the winnowing fan (1000 rev/minute). Some stuff we built using direct shaft drive, with flexible couplings - that was very effective also - e.g. a larger grain mill driven at 60 rev/minute from the end of a single pedal unit shaft - at first from memory we used a commercial flexible coupling (e.g. manufacturer Fenner from UK), then we worked out how to make our own with the rubber disc made from old car tyre - highly effective. The thresher/mill in this report has a nice layshaft running at 200 rev/minute. The mill is shown here as an integral unit, but anything could be pulled on to the end of that layshaft using a flexible coupling or a direct solid coupling and a torque arm (if the device is light enough).
Wooden vs Steel Frame construction - at the start (Uganda 1972) I was a bit over the top with wood, thereafter I was a bit over the top with steel. Stupid really. It should depend very much on the relative costs of sawn timber vs. Steel sections and their relative strengths and the cost of fastening techniques. We never really checkout out that kind of stuff - bad. And what about unsawn timber, bamboo etc - interesting possibilities - also to combine some traditional materials such as unsawn timber and bamboo with modern joining techniques and some modern but relatively low cost components.
Flywheels - the original flywheels of solid cement in bicycle rim and spokes were very effective but a bit heavy. Maybe keep the inner ring free to loose only a small bit of the flywheel effect but to lose a lot of the weight. That was a copy from a VITA report on a wood turning lathe. The thresher as per this report does not need a flywheel - the drum itself has enough momentum. A plate mill type grain mill running at 200 rev/minute with 4 pedallers does not need a flywheel, but a single operator running at 60 rev/minute would need one. The one-man and 2-man pedal piston water pump designs used a steel rail (as in disused rail track) hexagonal flywheel arc welded together which was very effective - not too heavy but with plenty of momentum.
Threshers are covered here
Grain Mills are covered here and/or are easy to adapt
It might be possible to drive a small laboratory-type hammer grain mill (or home-made copy of that design) as fast as 8000 rev/minute using 2 stage belt drive. We never went that far.
Maize shellers - we adapted a small commercial single-hole maize sheller from 60 rev/minute hand cranking to 200 rev/minute chain drive from pedal mechanism (see photo in this report). Also a commercial hand cranked 2 hole maize sheller again from 60 rev/minute hand cranking to 200 rev/minute belt drive from pedal mechanism (see photo in this report).
Winnowers - we never messed with the sophisticated ones with shaker trays and sieves, but made a nice one with a plastic car fan running from a single pedal unit at approx 1000 rev/minute through single stage belt drive using hollow circular polyurethane extrusion emergency fan belting. The airflow at about 30 degrees from horizontal blew between a hopper and collection sack with holder. Such a unit could be easily made as an add-on to the machine described here. I would recommend a home made sheet metal fan cut from one piece of 0.45 mm thick galvanised steel sheet and bent to shape. We used a bicycle front hub for the fan bearing unit with a small (30mm diameter) 2-piece wooden pulley sitting on the other end of the spindle from the fan.
Water Pumps - we made a nice 4 man pedal centrifugal water pump running at 3500 rev/minute through a 2 stage chain and then belt drive. We sold that to UNICEF and it finished up at Karen Village Technology Centre Nairobi before parts got stolen or removed from it. But small centrifugals are a bit inefficient, so we moved on to the 2 man Trolley Pump design. We actually had to play with (cut and shorten) the sealing spring on that unit to reduce drag and efficiency losses to an acceptable level. There could still be some mileage in that kind of design, depending on cost of the pump. One could even probably fabricate the pump body on a small-scale basis but buy in the plastic impellor, seal and spring (and of course bearings).
It could be interesting to design and produce a hybrid wind-powered and man-powered pump based on the 2 man trolley pump unit... In fact any wind powered unit should always consider man or animal power as a backup strategy for windless periods.
Sugar Cane Crushers - we made a nice one of these for animal power, using 2 x 6 inch diameter (150mm) steel pipe rollers with gripping splines created by arc welding, and running in wooden bearings of about 30mm diameter (from memory). We powered it by the ox pulling a rope running around one of those rollers extended, therefore powering only on the outward walk and resting on the way back in (the walk was about 30 metres I guess). That project was really popular because the stuff turns into alcohol with almost no encouragement... To change that design to use ball or roller bearings would produce a very big improvement in efficiency.
Summing up, we tried a lot of stuff, some of it undocumented (and even regrettably without photos - we should have snapped everything we made in those days - most of it was good). And there were ideas we should have tried out which we didnt. Anyone doing any kind of stuff like this needs to keep a very open mind. Feel free to run ideas across me anytime by email at email@example.com.