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| *Vultures Knob>>>Bike Pedals |
Would a muscle powered hybrid make sense for a boat's drivetrain? |
I am planning to build a muscle powered commuter boat, using pedals, as on a bicycle. Now one of the challenges I face is transferring as much of the human motion as possible to the propeller. I am not sure how much of a loss through friction there is when using steel gears or other setups, but I just had this idea pop up in my head instead: What if the pedals only drove an electric motor, which generates DC electricity, which is then transferred straight to an electric motor driving the propeller? The advantage of that would be that I could also feed solar or wind energy into the whole thing, somehow (that one needs some more brooding over, I know). But would that make at least a little bit of sense, or is this hopelessly inefficient? Tahini: You should concentrate on the "muscle to electric generator" interface, with which you generate electric power or propel your craft. Reasons for my "warning": 1. Muscle Effciency. One of your issues is the vast difference in efficiency of the human muscle as a function of its contraction speed (from near 100% down to maybe 10%). The automotive equivalent is the well known "torque vs RPM" plot. Your muscles in effect perform like a race car, their plot being a steep "needle", in comparison to a more desirable FLAT torque curve. Incidentally, that is why a bicycle needs so many "speeds": You are never pedaling at the optimum RPMs. 2. Physiology: Your heart "operates" at an average of < 50W. But its peak loads can be as high as 1000W (1.5HP). Incidentally, that is why a human pedaling a bike is so "superior" to any gasoline or electric "assist engine", which provides such peak performance only when the engine weighs several times as much as the bicycle. ==> 3. What I am driving at, is that "constant RPM pedaling" is NOT the best or even a desirable mode of power generation/ motion. You should study the physiological load cycles and especially the seating position of your driver, before you finalize the drive train in your water commuter craft. E.g. a constant repositioning of the driver may give a much better efficiency, by as much as a factor of two. Note, there is a wealth of information in your university's library on the physiology of Aleutian Inuit kayak paddlers (no kidding). They are the highest efficiency "propellers" known among us humans. Also, you might want to consult the physiological data base on the pedal propelled "Gossamer Albatross Human Flight" project. I do not know if he is still around, but Dr. Paul MacCready from AeroVironment in L.A. has spent years studying your issue. MacCready was also a professor at Caltech in Pasadena. ---------- Finally, please take a look at the first SERIOUS attempt of an electric bike. To be introduced shortly here in the US by Schwinn. The components used in that bike, Lithium Polymer battery, shaft drive (i.e. no chain), and the planetary 6-speed transmission might be ideal also for your project. Source(s): http://www.google.com/search?client=fire... http://www.schwinnbike.com/products/bike... http://www.dfrc.nasa.gov/gallery/photo/a... http://en.wikipedia.org/wiki/gossamer_co... If you get a highly efficient motor, generator,transformer,controll... you would drop around 10-15% (at the best) If you start using brushed dc motors and car alternators it's going to be very bad. Seams to me you would have to use about the same number of gears to run both setups. I think the best idea would be to use a booster motor with human power. |
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