po rcgroups Mega thread
http://www.rcgroups.com/forums/showthread.php?t=1097355--TIP 7: Braid or twist power distribution wires to minimize Rf emissions. Also see the Wiring info for multicopters section, particularly TIP 6 for EMI issues that affect the compass and magnometers. Info here:
http://www.stefanv.com/rcstuff/qf200406.html Use only the lightest gauge wire necessary to carry the current load required for your quad to save weight. Examples: A quad with total ~30W hover: Lipo to wire harness 16g, ESC wire harness 18g, harness to board 20g. Design your harness as light as possible if using any fuses or hardware in order to save weight too.
There has been no problem running either the ESC pos/neg power wires or the wire to the motor in lengths of up to 40cm. Electrical Engineers recommend adding a 220uf-440uf xxV low ESR electrolytic capacitor between the +/- ESC power wires after that length and every 10cm after that in order to minimize ripple current which can damage ESCs over an undefined extended period of time. The xxV value should be at least double the voltage being used to power the ESC, i.e. 4s use a 35v value for the capacitor.
You will use less wire and therefore have less weight if you run the power wires out to the ESCs. The ESCs will perform better when cooled by the airflow of the props.
Longer motor side lead length does effect the back emf detection of the controller, so the longer the leads, the less accurately and efficiently the motor will be run. So if you need to lengthen wires in a specific installation, doing it between battery and ESC is the safest approach and in a multicopter application has the additional benefit of offering cooling air from the prop wash. For additional technical info see Rusty's ESC testing in in the motor section above and the "Extending brushless cables thread" particularly the posts made by Patrick del Castillo of Castle Creations(Patrick) and Whanderson(Bill P.), a NASA engineer and this thread on ESC capacitance recommendations:
http://endless-sphere.com/forums/vie...22194&start=45.