NEVER connect a Capacitor backup or voltage protector on APM board


Edit : from the posts below I deduce the issue seems specific to my config. Threfore I remove temporarily my request to add a line a caution in the wiki as it might not be a general problem for everyone, until further investigation and identification of the root cause.

This post is a follow up of this one :

I purchased this capacitor to serve as an APM power protection:


I thought this would protect my APM from very short voltage drops and ultimately avoid erventual APM resets in mid air. WRONG.

I connected this capacitor on the A1 to serve thus as a short power supply on APM.

What happens then when connected ?:

multicopter is on the ground (after landing for example), motors are armed, throttle is at zero. Then if you turn your radio off -> RTL is triggered ! -> motors start full throttle to reach RTL altitude. (of course at the same moment your radio is off so you can only observe a flyaway)

This behaviour was tested and repeated multiple times with same results (on my config).

Another scare we can avoid...very very bad idea this stupid capacitor.

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Maybe it's an attempt to slow down the cloners? Not cool and not in the spirit of open source! Reminds of the days when Apple would trip up the jail breakers on each revision of the iOS.

Maybe it's people not understanding how Eagle works?

It seems that we are not looking at the full picture in Eagle


Thanks to Chris Card for peeling back the layers and finding the 5V connections.

I knew they had to be there. Even with his post, I had trouble seeing them with this laptop display. Well done Chris Card!

When looking at the Eagle files, not everything called a layer is an actual layer of circuitry.

Names of parts, artwork, etc are considered layers also.

Here is my version of Chris Card's inspirational information...

+1 for Bill looping post back here.


Thanks Stephen,

The schematics I'm pretty ok with, I just don't have experience with Eagle. Most of my previous board layouts where done using OHP film, laser printers (when they cost $1000s) and UV exposure boxes. I helped test a 8051 dev board my tutors built, but hey it was 1989! I think they used eagle but my memory is a bit hazy ( see ) The way eagle works it feels like I am in a time machine though! lol

I still don't understand your initial concern. What sort of behaviour were you expecting? With the copter armed and tx switched off, of course it will go in rtl. 

Going with your description this hasn't anything to do with backup capacitor connected or not. It's just how it's supposed to work. Don't switch off your tx when the copter is armed. Except when you want it to come home and forgot to assign a rtl switch of course.... :)

Hello Zidlov, no the expected behaviour is "disarmed" when throttle is at zero and on the ground.

Anyhow, sse my post edit : it was an electrical problem specific in my setup that caused this unexpected behaviour. Solved since then.

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