Hummina Shadeeba said:
how efficient will this end up being compared to a using the same motor with the typical 3:1 or 2:1 gearing. With rpm x torque = power, and no ability to get that rpm it's going to have to compensate for lack of rpm with more torque and that sounds like amps.
Justin did you do any comparisons with your 1:1 board vs a geared for amp draw?
Without gearing you need more motor/magnet mass to achieve the same efficiency under load. If you account for this, then the efficiencies are comparable going up hills, and even better on the flats and at light loads since there are no belt/transmission losses.
But if you ran the identical motor, in one case in direct drive and another with a gear reduction, then for sure you would see more amperage draw and less efficiency with the direct motor arrangement going up hills. At low loads, the direct drive would still be better because of no transmission losses and (more importantly) because of less than half the core losses too, as a result of the motor spinning at less than half the rpm. So over the course of a trip though, you usually burn through more Ah going up the hilly bits than on the flats, giving the geared setup an advantage. Over a typical trip the geared down drive would have a lower net Ah consumption than direct coupled
if you use the same motor, but in practice you wouldn't do it that way, you'd spec the motors accordingly.
The result is very much like the geared vs. direct drive hub motor debate, where in the end DD motors wind up being about twice as heavy as a geared hub for similar torque output, and get better mileage with some types of terrain (flat and fast) while getting worse mileage on the slow steep hill climbs. There's no clear winner, both are viable with their respective pros and cons.
Personally, I don't mind a somewhat heavier motor in exchange for the shear mechanical simplicity and beauty of coupling to the wheel with no transmission. If someone's objective is the absolute lightest board, then there's no doubt the belt drive reduction is the way to go. If cost reduction is the goal, then a belt drive makes sense too, because motor materials (copper and rare earth magnets) are much more expensive than timing belts and pulleys, and if you can trade the former for the latter then you should. If efficiency is the goal, it could go either way.
I'm not sure what others with eboards are logging for their energy consumption, but we're usually getting about 10-11 Wh/km with the direct drive eboards going at 30-35 kph cruising speeds riding in traffic with associated stop and go. Pretty similar to an ebike.
-Justin
