Here is another lot for your amusement. If you have been following some of my posts on playing around with the Brodak electric Super Clown, you will know that I have been trying to see how light weight I can get the battery down to. My theory was that it would be more efficient to turn a larger higher pitch prop (10-6 to 10-7) slower than the smaller low pitch prop (9-4 for example). I think I am basically correct, but I am not convinced that I have a better flying plane than the original setup. I need to reinstall the original setup and fly the SC again just to see how it performs.

Anyway during my trials I begin to think I understood how the ESC worked. As I now mind out, I was completely wrong. First, I should note that the battery current you measure  (in my case with an Eagle Tree Data logger) isn't necessarily the motor current. It is for wide open throttle, but at reduced throttle, the ESC really does a marvelous job of basically converting the high voltage low current from the battery to a lower voltage higher current in the motor.

In the following plot (two flights flown right after one another), you can see how my Super Clown behaves with a 2 cell 2500maHr Lipo and then in the second flight with a 3 cell 2100maHr battery. The motor in both cases was the Brodak Stock motor, the ESC was a Castle Creation 35A Phoenix running in Governor mode. The timer was the JMP-2. The prop was a ACP 10-7 thin electric. The dark purple trace is the battery current, the lighter violet was the rpm (started at ~8500 rpm). The most obvious thing is that the initial current (level flight is ~27 A for the 2 cell case, but only 19A for the 3 cell flight.) This is pretty close to the 2/3 ratio of the cell count.  The 2 cell flight drained the battey by about 2200maHr, the 3 cell flight about 1700 maHr. I should say that the 2 cell battery couldn't sustain the 8500 rpm through the entire flight (and so isn't adequate for this prop and setup).

When I look at the power, I find that the ESC with the 3 cells (at reduced throttle) is about 95% the efficiency of the 2 cell battery (which is running near wide open throttle at the beginning. I think this is pretty amazing and good news to me at least!

Alan

Igor,
I don't think that is quite right since the motor inductance averages out the current. I think in both cases the motor current is about the same since the prop rpm and load is identical (at least at the beginning of the flight).

This was a major advance of the higher frequency ESC's as compared to the older ones which worked at 50Hz (rc receiver frame rate). These were so slow that the motor really did react (accelerate and decelerate) to the higher current pulses (max width =20ms) . My old ESC (built into a Futaba receiver from 1991) actually "growled" at low throttle. These weren't so efficient as the higher frequency ones.