Savage Flux XS Castle Electronics Question

[Pdelcast]

Originally Posted by fastbaja5b

I've been told here that a 30 odd amp jump is reasonable for 200kv, so by that logic, if I go down from the 4000kv to a 2000kv, my battery should be getting charged as every 200kv drop is a 30 amp drop? Doesn't make sense.

Well that's just silly.


Going from a N38UH magnet to an N35UH magnet is about a 8% decrease in air gap flux. This causes the kV to rise by about 8%.

A Castle 3800kV motor is about 3770kV actual.

An HPI 4000kV motor is about 4050kV actual.

They have exactly the same DC resistance.

So the difference in current maximum is determined by back-EMF. Because the HPI motor has lower back-EMF, when using the same gearing and throttle ramp rate, the maximum currents will be significantly higher.

Your observed 30% maximum current difference is about right, and doesn't have anything to do with how the motor is constructed. If we made you a custom 4070kV CC 1410 motor (by shortening the stator stack and magnet) the peak currents would also be about 30% higher than the CC3800kV motor.

IF you change the gearing so that the HPI motor is geared approx. 8% lower than the 3800kV CC motor, you should see about the same peak currents.

OR - if you change the throttle ramp rate by 8% (using punch control or torque limiting) you will see about the same peak currents.

It's just that you can't compare peak currents on two different kV motors side-by-side without making a similar gearing or throttle ramp rate adjustment.