ORIGINAL: wollins
I have the impression that motors "draw" amps based on the prop selection, and the esc limits that draw so it doesn't burn the motor ... In other words ... an 8 cell battery will send 9.6 volts to the motor which will "draw" x amount of amps based on its prop. Am I anywhere close to being right or am I REALLY totally confused? :-)
If I am right how do I calculate what amount of amps different props generate based on what battery etc? HELP!
The ESC doesn't limit anything. That kind of circuitry is enormously large, heavy, and expensive, three things that we don't want in our airplanes
Some more advanced ESCs have overcurrent protection in them, that causes them to shut down if too much current is sensed, but most will simply burn out, or allow the motor to burn out.
You have it mostly correct, though. The voltage does play a large part in how much current passes through the motor, as does the propeller. Much of what determines how much current flows is the design of the motor: The length, gauge and quality of the wire that makes up the windings, the length and diameter of the rotor, and the strength of the magnets all play a role in how much current is drawn.
Unfortunately, there's no simple way to calculate it, no formula you can plug in the numbers and "turn the crank" on to get a prediction as to what will happen. There are simply too many factors involved, as you've seen above. It's necessary to use a computer simulation such as Motocalc, Electicalc, or the online PCalc at
www.flydma.com to get an estimate, but ONLY an estimate. These programs ignore many other factors such as atmospheric conditions in your area, variations in quality, etc., that can have a HUGE effect on the behaviour of your power system.