Torque and RPM Graph for Castle Creation products ?

[SpEEdyBL]

Originally Posted by othello

Thanks Patrick for sharing this graph with us. Just saw it and a few questions came to my mind.

. When multiplying 16Vx2200kv you will get 35200rpm. Your graph starts above 36000rpm which would correspond to a 2250+kv motor at 16V. I guess this is due to slight input Voltage variations and/or that a 2200kv motor will never be exactly a 2200kv motor.

. I must admit that i badly missed an Amperage curve on this graph ;-) First it would have been interesting to correlate Amps to torque. And secondly it would have shown the Amp range at which efficiency is at its best.

Which leads me to a few theoretic questions.

If one changes input voltage to say 14,8V (4), 18,5V (5) or 22,2V (6s):
. Does torque stay at the same level if you feed this motor with a given Amperage (say 20A) for all 3 voltages?
. How will the efficiency curve shift with all 3 voltages? Can one say that when you apply higher voltage, the efficiency curve will rise earlier with lesser Amps and might fall off earlier with higher Amps when compared to lower voltage applied?

And there is one thing which always intrigued me when it comes to voltage / wind choice for a certain motor. Is there a slight advantage for lower wind motors when it comes to absolute high power levels. And if so ... why? Better copper filling? Can one really expect the same power output from a Castle 1515/1Y (2200kv) and maybe a future Castle 1515/2Y (1100kv)?

1. Torque is directly proportional to current (independent of voltage), unless (as described earlier) the stator is oversaturated. However, a good motor is designed so this cant happen within it's specified voltage range. Think of voltage proportional to theoretical rpm i.e. volts x kv, current proportional to torque, and efficiency at high loads approx. = actual rpm/(volts x kv).

2. The equation for % efficiency of a motor is (VI - rI^2 - I0)/(VI) where V= volts, I = amps, r=resistance and I0 = amps at no load. So if you plot the graph as % efficiency vs. amps, you will see that if you use a higher voltage constant, you will get a higher max efficiency. But keep in mind this is only a theoretical equation and at some voltage, the efficiency starts to get worse. This voltage where peak efficiency is the highest is known as the sweet spot of the motor.