Buying motors is easy. Building them, not so much. Although neither a suitable controller nor vehicle/display stand has been found for this motor, it's probably one of my most beautiful projects. The vehicle this was designed for is referred to as an 'electric kick scooter' because the motor is integrated into the rear wheel and the whole vehicle looks like a chunkier version of a razor scooter.

 

All parts were made by hand, besides the stator, which was recovered from a large photocopier. Wrapping the stator took about 12 hours and was difficult yet rewarding.

 

Calculations:

 

I want to climb a 10% grade:

 

F = mg sin(theta)F = 75 kg * 9.8 m/s^2 * .1

F = 73 N

 

I want to climb the hill at 5 m/s.

 

P = linear force * linear velocity

P = 73 N * 5 m/s

P = 365 W

 

Torque = Force * radius

 6" diameter wheel = .076m

 

T = F * r

T = 73 N * .076 m

T = 5.55 Nm

 

33 volt LiFePO4 battery.

 

365 W = 33 v * 11.1 A

 

T = 4NIBLR

(Torque = 4 * # of wraps * Current * Strength of magnetic field * Length of stator * Radius of stator)

 

Estimate 1 Tesla.

 

T = 4NIBLR

N = T/4IBLR

N = 5.55 Nm / 4 * 11.1 A * 1 T * .0254 m * .034 m

N = 144 wraps per phase

 

Max current through 4x22 gauge wire = 40 A 

N = 40 turns per phase.

If A = 11.1, N = 144

If A = 40, N = 40

 

Torque constant, in Nm/A.

 

Kt = T/I = 4NBLR

 

For 11.1 A we get .5 Nm/A

For 40 A we get .14 Nm/A

 

1 Nm/A = 1 V/(radian/s)

 

33 v/(.5 v/rad/s) = 66 rad/s

33 v/ (.14 v/rad/s) = 236 rad/s

 

66 rad/s * 1 rev/2 pi radians * 60 s/1 min * 60 min/1 hr * 2 pi (3 in)/1 rev * 1 ft/12 in * 1 mile/5280 ft = 11.2 mph

 

Try 72 wraps (experimentally determined maximum)

 

Kt = .248 Nm/A

 

5.55 Nm / .248 Nm/A = 22.4 A

33 v/ .248 v/rad/s) = 133 rad/s

 

130 rad/s * 1 rev/2 pi radians * 60 s/1 min * 60 min/1 hr * 2 pi (3 in)/1 rev * 1 ft/12 in * 1 mile/5280 ft = about 22 mph!