SamTexas said:
Brushed motors: Yes, two of them, one for each rear wheel. Assuming the worst: Twice as inefficient as brushless motor.
Gearbox drag: I don't know. Do they have a gearbox? Multiple automatic gears or are we talking about the typical one gear reduction like a geared hub?
Usually the brushed motors run thru a gearbox, usually a right-angle one. I used these mtoors to run CrazyBIke2 and got much better performance out of them than a powerchair does, because I ran them thru the bike drivetrain so they didn't take so much power at startup and low speeds.
Generally these things are geared really low, so they can move really hefty loads slowly but definitely, so no one gets "stuck" because it won't start moving from a stop under most normal conditions.
Another issue is that these are heavy beasts and the tires are usually "airless" foam-core tires, rather than pneumatic. So there's more rolling resistance (sometimes a LOT more). Part of the weight is meant for ballast, to keep the chair from tipping in sharp turns or on slopes like ramps or crawling over a curb (for those capable of it).
Not all the motors used are brushed, though. These days there are a number of brushless hub motors in use. I have one of these to power a new bike build; testing thread is here:
http://www.endless-sphere.com/forums/viewtopic.php?f=30&t=32838
It's massive, and I don't yet know what kind of power usage it has under load, but it is less than 2A without a load on it at 40V+ full throttle using an EVAssemble 12FET.
For various reasons like steering/etc., I think your low expected wattage numbers are off, but I haven't checked them against anything (including the powerchair I have here). The reason is like you say, there's no huge heat buildup from inefficiency, so the power must actually be mostly going into the motion of the vehicle. Typically there are two 300-350W motors per chair for the smaller ones, and two 600-700W motors for the larger ones, when they are the brushed/gearbox kind. I'm not sure what the rated wattage is for the brushless monsters like I've got in that thread above.
REdiculous is probably right about the RPM stuff, and Burgerman expands on that. But I wouldn't change the grease in there unless it's trashed. I've changed grease in one to new stuff and it made no difference to anything, except that the thinner stuff I tried leaked thru the bearings into the motor itself as soon as it warmed up.
That was a huge mess.
Burgerman is right about the steering and resulting power usage due to slight inclines, etc.
I suspect it has something to do with the braking systems. The vehicles do not have brakes, the motors handle the braking when you let go of the throttle.
They usually do actually have brakes of a sort, but only parking brakes, usually, to lock the wheels in place when stopped. BUUUT: As Burgerman points out, the brakes use notable power because they must be energized to allow the motor to spin at all; a solenoid is used to pull the clutch out, basically like an air conditioner compressor in a car. They are done this way so that a total power failure will not leave the unit rolling down a hill, but will instead lock it into place, which is usually safer for someoen that can't do anything about the situation.
