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Old 02-21-13, 05:07 PM
  #19  
turbo1889
Transportation Cyclist
 
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Join Date: Aug 2011
Location: Montana U.S.A.
Posts: 1,206

Bikes: Too many to list, some I built myself including the frame. I "do" ~ Human-Only-Pedal-Powered-Cycles, Human-Electric-Hybrid-Cycles, Human-IC-Hybrid-Cycles, and one Human-IC-Electric-3way-Hybrid-Cycle

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I don't disagree that personally I prefer to mount the motor(s) in the frame and run the power through the same chain as the human power. The main reason being the availability of having more then a single gear ratio, and yes the weight, and to a certain extent the efficiency as well.

It is true though that hub-motors do have some advantages to them as well though. Namely, for conversion builds, it is really quick and simple to just swap out a wheel and wire it up. In addition there is the RPM advantage. Depending on wheel size and gearing the RPM of the wheel is usually at least twice that of the crank and so there is less of a step in gearing required to match motor to wheel speed then motor to crank speed considering that all but the most obscure electric motor designs put out considerably more then 90-RPM in the peak power and efficiency ranges. Using a jack-shaft or applying the power to the chain in-between the rear wheel and crank is one way to get around this (and the method I am planning on using with this build) but never the less it is a factor. Hub-motors that are not direct drive but use an internal planetary gear reduction inside of the hub are considerably lighter weight and more efficient then direct drive hub-motors but at this time not as reliable primarily because almost every single one of them currently on the market uses weak plastic planetary gears that wear out over time and can be damaged under heavy load.


I'm talking about taking the considerably lower weight and better efficiency offered by an internal gear reduction hub motor and improving it with quality honed and lapped, heat treated steel wish-bone helical gears in the reduction stage just like top end quality internal gear hubs use to provide lifetime service with proper maintenance and smooth clean high efficiency drive. Currently almost every internal gear reduction hub motor uses cheap junk low grade rough cut simple spur steel ring and sun gear with plastic planetary gears (I've heard rumors of one that uses bronze planetary gears but have yet to track down the rumor to an actual product with that confirmed feature).

Then taking things even further and inside that hub motor along with the reduction gears include a second planetary race of internal hub gears of equal high quality construction to provide a 3-speed rotary shift standard 3:4, 1:1, 4:3 ratio spread. The power of the motor being reduced down to a usable RPM by the first stage planetary gears that matches the human input power the input sprocket on the right side of the hub for the drive chain off the crank and that combined power of the motor and the human input run through the second planetary race together which offers three switchable gear ratios to the final output to the wheel. You would need to use a slightly larger reduction ratio then standard for the first stage reduction from the motor so that your top end 4:3 ratio #3 gear on the internal hub would represent top end speed on the flat and the two lower gears would be for hill climbing.

I'm not saying I'd consider such a motor for this build since I need a wider gear range then the 177.8% that a standard ratio 3-speed IGH offers since I want to be able to haul a considerable amount of cargo up a good hill in the bottom end of the gear range and still get top speed on the flat running light with no cargo on the top end of the gear range, so that wouldn't be wide enough for my needs with this build. But if such a hub-motor existed for a regular motor assisted bike for non-cargo hauling purposes simple transportation only it could certainly be an option that could hold its own against many mid-drive arrangements breaking even on weight and efficiency and covering for its narrower gear range by its rugged compact simplicity with everything built into a compact size in the rear wheel hub, especially for upgrading a standard bike by just swapping out the rear wheel. Using a pancake disk type motor instead of radial can type motor could make it even better especially for an aerodynamic road bike with aero-wheels where the disk could be built into a smooth continuous spoke-less disk type aero-wheel.

It's and idea I've had for a while, namely nesting an internal gear hub inside of an internal gear reduction hub motor to improve its performance by offering more then one gear ratio to the drive wheel and in the process upgrading the quality of the gears by using the same quality metal gears as used in the multi-speed gearing of the hub on the reduction stage from the outer motor ring. These pancake disk motors could allow the idea to be taken even further. Wouldn't completely replace a mid-drive arrangement which still has the advantage of more gearing ratios with a wider over all range but would be far superior to current hub-motors without giving up any of the advantages of hub-motors, namely their simplicity and quick swap in set-up.
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