we were able to source some good carbon fiber tubing with the same outside diameter but slightly thicker inner diameter (which will surely strengthen each boom at the motor mounts and where they attach at the frame. Bigger props on the bottom? i was figuring smaller on the bottom due to downwash from uppers. i'll have to try that and see how much of a gain we get. thank you. im still needing to know what i need to do to run more than one battery....any suggestions