Why fullsize PDBs like Nucleus or Overcraft are crap

03 08 2015
TL;DR: 
Fullsize PDBs are crap because its only a thin layer of varnish which seperates your carbon frame from burning.

My quads are all broken atm, so no flying for me. Tinkering time!
I had a friends ZMR250 on my desk to analyse its odd behavior. Its Nucleus' red LEDs were sometimes dim and sometimes off, strange effects prevented the FC to boot up some times and it behaved weirdly in general.


While I was twiddling on the LEDs to check if one came loose with a screwdriver the LEDs suddenly lit up. I pulled the screwdriver away and they slowly dimmed off. Strange. Fiddled a little more and noticed, that they lit up whenever I was shortening their circuit through the copters carbon base plate.  Oops, ground was leaking somewhere from the battery to the frame. Tested with my multimeter and indeed, there were 12V between the main body and 2 arms and the battery's positive terminal.


Disassembling the copter I found this under one arm:


Various crashes removed the varnish which separated the arms from the PDBs negative bottom side. The other arms showed similar wearing. A layer of insulating tape fixed that problem, for now:




">"> Ok, the voltage leakage is no more - but for how long? This copter will still crash now and then, parts will move, insulating tape will wear off. 


Why is that bad?


Cars and many electrical devices connect ground to their metal body. In fact, the body is used as ground terminal and replaces the black wire in many cases. This is a good thing for safety and saves a lot of wires. But a multicopter frame is not made of well conducting metal, but bad conducting carbon. The cars electric components are built with negative charge of their frame in mind, multicopter parts are not.
When a battery's XT60 connector or any other wire is dangling loose and accidentally touches the frame while it is connected to the other terminal, current will find the shortest path to close the circuit, carbon will glow and burn, your battery will swell or burst.


PDBs like Nucleus or Overcraft consist of 3 layers, both outer sides consist of copper, one side is positive, one negative, and the center of fibre-reinforced plastic to seperate them from each other. The copper surfaces are covered with a thin layer of varnish to prevent short circuits. From this it follows that this type of PDBs is simply unsuitable for any frame, where there are conductive parts directly touching the PDBs surfaces. Parts move, varnish will wear, ZMRs will burn.


Kommentare

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03 08 2015
#1 Armin (Antwort)

guter Bericht, trifft voll in's Schwarze! wer zuverlässige Kopter bauen will. lässt das PDB besser weg..meine Erfahrung.

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