Building hub motors

#1
Hi, I came to this forum to ask a group of people who are familiar with hub motors about my project to build hub motors for my brother’s power wheelchair. We’re building an all terrain power chair from the ground up. Most power chair companies use brushed DC motors because of their fine control and ease of maneuverability at low speeds. The only issue is that they’re inefficient, the brushes wear out over time, and the chain driven brushed motors (21st Century Scientific ST4) on his current chair (Bounder Plus H-frame) cost nearly $4000 each. They’re awesome motors with a lot of torque, which is what we’re looking for, but they’re also very large and heavy.

I’ve done a lot of reading and research on BLDC motors, and I work as a custom metal and wood fabricator. While there is only one BLDC hub motor chair that I know of (made by Golden Motors) I’d like to know why other companies haven’t tried developing these. I undestand the anatomy of the hub motors, and have sources that can laser cut laminations for the stator windings and machine parts for the rotors, bearings, and hubs.

I would just like some input and advice in terms of technical details like how the number of poles, stator teeth, phases, windings, wire gauge, and concentration of winding affect Kv, Kt, and heat. Also, what combination of poles, stator teeth, and phases produces a balance of the most torque while minimizing or eliminating cogging? I’m leaning towards a fractional slot style over the integral slot style to prevent cogging.

As far as my parameters for these motors, they need to be approximately 6” in diameter and 6” wide. They we’re looking for about 450-500 max rpm, but we can tune that down with a controller. As far as torque, I’m not sure about any specs (our current ST4 motors are proprietary, so they won’t release specs). He is currently able to push a snowplow, climb steep grades, pull a 16’ inflatable raft through the grass, and even pull a car slowly on a flat grade. We’d like to have this much power in our new motors. With our li-po battery, we’ll be able to exert about 300amps @ 48v. They need to be able to maneuver finely without cogging. I know that BLDCs are inherently bad at low end torque during startup, but I’m hoping we can figure out a way to overcome that.

Any help would be appreciated, and thanks for your time.

-Ryan