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Let's say you are traveling at a constant speed 'v' on flat ground.
Let F_b be the positive force the battery is providing.
Let F_m be negative force from loss in the motor (electrical power going to the motor).
Let F_c be the negative force from loss in the controller.
Let F_t be the negative force from transmission and motor spinning (no electrical power going to the motor).
Let F_w be the negative force from the wind.
Let F_r be the negative force from the rolling resistance.
Since the acceleration is 0 (constant speed), the net force is 0. So,
F_b(v) + F_m(v) + F_c(v) + F_t(v) + F_w(v) + F_r(v) = 0.
It would be nice to have a graph with lots of points for each force function.
We can do that for F_w and F_r. F_r is approximately constant. F_w(v) can easily be found for any v. F_b(v) was found already. It's just V*I(s)/s. To find as many points as you want, you just need a volt meter and an ammeter. You can find F_c(v) by knowing the voltage drop from the mosfets in the controller. For my curtis controller, it's about a 0.5v drop at 100 amps. So, it's about 99% efficient. So, I think I'll just assume F_c(v) is approximately constant. I'll say that
F_c(v) = -0.01*F_b(v)
It's not perfect, but pretty accurate.
To find F_t(v), do the experiment where you let the car slow down, but leave it in gear. Then do the experiment again in neutral, and find the difference.
All that's left is F_m. So, you can figure out the loss from the motor for a variety of speeds (assuming the motor stays at an approximately constant temperature) by solving for F_m in the above equation!
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