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Im trying to build an electric wheelchair with mecanum wheels, and as you might know, each of its 4 wheels has to be independently powered for the chair to have holonomic motion.

With my desired speed to be around (brisk) walking speed only, say 1.15 m/s, and my mecanum wheels sized with a 4-inch radius, I know that I'm going to need a very low RPM (by my computations, ~110 rpm).

However, my computed power draw per wheel is around 300W, which is way large, that I am not sure if I am on the right track? My load capacity is somewhere around 136 kg, btw.

This brings me to my question: are my torque/rpm/power calculations correct??

per wheel:

r = wheel radius = 4 inches = 0.1016 m

circumference = 2pi(r) = 0.638 m

v = (max) running velocity = 1.25m/s

rpm = v(60/circumference) = 117.48 rpm

the chair:

u = coefficient of friction = ~0.7

N = normal force = mg

m = total mass (136 kg)

g = 9.81 m/(s^2)

vi = 0 (rest)

t = time to accelerate, say 2 s

a = acceleration = (v-vi)/t = 1.25/2 = 0.625 m/(s^2)

Finally:

Ftotal = uN + ma = m*(uN+a)

Fwheel = Ftotal/4 = 255. 248 N

Twheel = (Fwheel)(r) = 25.93 Nm

Pwheel = (Twheel)(rpm)(2pi/60) = 319 W

Is the power really supposed to be this large and my RPM that low?

Help/corrections would be very much appreciated!