BLDC motor flavors

[anvoice]

I'm curious about a certain topic: looking online, I find some 36mm diameter BLDC motors rated for 5-25W (at 12V, so consuming about 2A tops) while other brushless inrunners can be found taking about 30A (on 3S-4S LiPoly batteries, and thus must be rated for several hundred Watts). So the question is: what would be the main structural difference between these motors? I'm guessing it's got to do with the number of windings, gauge of the wire used, etc., but could anyone provide an example of how the characteristics of one differ from the other (e.g. double the number of windings and performance changes in such and such a way)? Or point me to an information source? Thank you.

[firehopper]

I'm into rc airplanes, and brushless motors have so many differences.. KV rating, wattage, max voltage, number of poles. and so on. to be honest, I dont know how they would achieve that, but I would guess like you, different winding methods and different gauge wire.

[anvoice]

Yep, that seems logical. I just want to know what makes the difference between 20W and over 300W (at the same voltage). I'm holding the 300W in my hand next to the 20W, and the 300W one is slightly shorter despite accommodating an impeller, plus a little lighter. I wonder if a can rewind the 20W for a higher power rating, and how the KV, recommended nominal voltage, etc. would change as a result.

[mzzj]

Yep, that seems logical. I just want to know what makes the difference between 20W and over 300W (at the same voltage). I'm holding the 300W in my hand next to the 20W, and the 300W one is slightly shorter despite accommodating an impeller, plus a little lighter. I wonder if a can rewind the 20W for a higher power rating, and how the KV, recommended nominal voltage, etc. would change as a result.

Some possible differences:
-Cooling (still air vs huge propeller directly on the nose of RC airplane)
-insulation temperature limit
-magnet temperature limit
-lower loss stator iron (allows higher flux density and/or higher rpm)
-magnets and stator iron with higher max flux density
-and most importantly: rotational speed. There is not that much you can do about maximum torque in a given size of motor but if you can increase the max rpm from 3000 to 30000 rpm you get ~tenfold increase in output power. 

[anvoice]

The cooling issue can be mediated somewhat with an aluminum enclosure around the motor. It's true that some magnets can have a higher temp limit depending on the exact alloy.

I would still guess that those points are not enough to make an order of magnitude difference, especially given that these motors have a similar RPM at 12V. So there must be a difference in how they're wound, I just don't know that difference. Worst case I'll open them up and check, it's just that to count the loops I'd have to actually unwind the coils.