Very clear. I could have told you that wouldn't work.

I'm not wild about using the bottom two cells of the motor battery. The ESC designers went to a lot of trouble to optically isolate the high voltage section from the receiver. There is high current flowing in those two cells and it has what electronics guys call an AC component when it is at throttle positions less than 100%. Since current to the regulator is flowing in this same circuit the AC gets coupled into the input of the regulator. If the regulator filters this before it gets to the output and into the receiver you are okay but I'd be careful. I'll try to build one up and see what I can see.

Jim