two speed hub motor
Apparently I cannot over emphasize the need for gear enough. Hub motors that do not have a gear reduction inside must use more amperage to overcome the lack of gears. And that means that you will need a larger motor and battery, just to handle the increased amperage. It also means that you will end up turning your bike into an illegal motorcycle if you want to power 400lbs up an 8% grade. Or at least have worse mileage, and you could run the risk of burning out your controller if it is not big enough to handle the increased wattage.
When you use gears it really changes things. With gears you can move the "efficiency peak" around to match your mph. On a fixed hub motor you are permanently tied to your power-band and this presents a real problem at low speeds. Low mph/rpm on a hub motor places you into the low efficiency areas of the power-band. You can compensate a little if you have an ammeter and are really careful about using even less current than the current limit allows (so you are using almost no voltage down low in order to be more efficient) but you are still fighting a less than desirable situation.
Run a 40mph hub at less than 10mph under load and you'll cook it. My best guess is that a hub would have to be capable of better than 40mph to climb rough steep grades efficiently, and in that case you would not be able to do so slowly or you'd overheat the motor.
At 10 mph the efficiency is running about 50%. The good efficiency areas don't even exist until you are past 20 mph. So unlike with gears where you can "gas it" off the line and be in the good efficiency areas all the time, gearless hub motors have a real "issue" with quick starting. Quick starts on a gearless hub motor are really bad news for battery usage... (much worse than if you are geared right)
The only reason to even think about hub motors is because the speed of operation is lower (usually less than 500 rpm) so it makes finding sprockets much easier. An excellent example is the Elf car.
That's why they used one for the Stoke Monkey mid -drive.
Geared Hub motors verses Un-geared hub motors
Hub motor verses gears debate
While a single stage chain drive loses around 5-10%, a hub drive not operating near it's peak RPM is losing far more power than a properly geared motor would be.
San Francisco wheel?
Only in america can we use a motor strong enough.
Geared hub motors are intrinsically complex. Most direct-drive hub motors only have a few moving parts, and a hub motor with a gear set has tens of moving parts.
|The enabling feature of the GTF is its 3:1 reduction gearing. The setup is similar to this planetary gear system, also produced by Italian aviation company, Avio.|
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