The arms for the quadcopter had built in LED's onto the bottom side. If you read about my troubles integrating a lighting system into my DJI quadcopter, you'll understand why I like the idea of integrated LED's. The LED's are machine soldered in with resistors in between each one to keep them from burning out. The LED's definitely work with 2 cell LiPo batteries, but there were some concerns that they might blow out on a 3 cell so I just stuck with a 2 cell. On the top side of the arms there are 6 solder pads for attaching the 3 motor wires and the 3 ESC wires. At the end of the arm there are two small solder mounds that, when touched against the bottom plate of the frame, complete the circuit for the LED's.
The arms had 4 small holed drilled for mounting the motor into place. I mounted them so the wires pointed towards the inside of the arm.
I then proceeded to solder the motor wires onto their respective solder pads. I made sure to swap the order of the wires on two of the arms so that the motors on those arms would spin opposite to the other two. I finished all the solder connections before moving onto the bottom plate.