I want maximum power, which means maximum rpm (all winds can make the same torque and power is torque X rpm), and I prefer to stay below 100V. 2 turns are much harder on controllers as you go to high current due to the inductance being too low, otherwise that would be my choice. Gearing is wheel size and large wheels are geared too high (again regardless of the winding turns). That's why we see no electric motorcycles with large wheels running hubmotors, yet scooters can have sufficient power to drive a motorcycle. If the myth was true, they would simply put more turns on the teeth and make electric motos with hubmotors, but the physics don't work.teslanv wrote:John,
It sounds like you think a 3T (or whatever the "fastest" wind available is) is the preferred choice in every circumstance? Do I understand that correctly?
I understand that a 3T wind is better able to handle more phase amps than a slower wind, and that the amount of phase current a motor can handle before reaching saturation is directly related to the aggregate cross-dimensional area of the strands of copper making the circuit around each stator tooth.
Are there no circumstances where say you are limited to a larger tire diameter by design, that you would choose a "slower" wind motor for that specific application, provided it had the same total copper fill?
You light guys may be able to get away with the larger wheels, but it's a severe handicap, and so with the smaller wheel the fat guy in Costa Rica on the bike with a smaller wheel on a hubbie has more performance. I do have a set of 21" moto wheels (26-26.5" OD) ready to go on a build for road and trail use using a hubmotor, but that hubmotor won't be in the wheel so I can gear it properly. I'll gear it to the equivalent of about a 12" OD wheel and run high enough voltage to get the speed I want. Even below 100V I should be able to gear it for 80kph top end, and the gearing will be low enough handle off road without the complication of a 2nd set of sprockets to move the chain over to lower gearing for off-road. If it falls short I have high voltage controllers available, and I'll increase voltage 40-50%, decrease current 10-20% (for the sake of the controllers) and decrease the gearing by 25-30%. The end result will be even lower stress, more power, higher top speed, and more torque at the wheel. It's a 3kw rated motor like the Mxus, but not as rpm limited due to better steel and less than half the magnet poles, so the Mxus3000 could be run in a similar manner, but not similar extremes. You guys don't have the same load mine has to push, so your results could be quite similar though the big diameter motor will be harder for you to fit.
Regarding saturation, the beginnings of saturation are where increasing current results in progressively lower additional torque up to full saturation, which is the point where the electromagnets of the stator cannot be make more flux. The number of turns determines the current to get there, but that stuff all varies in direct inverse proportion with the current the copper can handle and make the same heat, which is why motors with the same copper fill are identical motors and winding doesn't change the wheel size they can swing. The only thing running higher turn count accomplishes is being able to use smaller wires, and that's a silly benefit to give up power in exchange. It gives up power because we are voltage limited, and you can't make up the difference with current.
All evidence contrary to these statements is anecdotal and not supported by the physics. Just because some guys are pushing low enough loads to get away with gearing too steep (large wheels) doesn't change the fact that they will absolutely get better performance by reducing the wheel size. They're commonly so steeply geared with the big wheel, that decreasing wheel size doesn't even change top speed, but the increased torque at the wheel is always noticed. Our hubmotor systems are very forgiving so these things can easily go unnoticed, but when you push the envelope that quickly rear their ugly head. That's why so many slow wind motors have been burned up by forum members pushing far lighter loads than mine push, and by mine I mean before HubMonster when the motors I ran (and are still running on ebikes) were identical in terms of the stator as Xlyte H40's. I'm not aware of a single speed wind motor getting burned up.