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Tuesday, August 24, 2021

Flag-Pin Power Switch Fail but Ultra Stick 10cc Ready!

My Spektrum iX12 Transmitter is back, and its time to move forward towards getting back to flying! I bound the Ultra Stick and the Pitts to it and programmed them in. Ran the engine up and made a couple fine tunes. 

At the end of my runs the power quit, and with diagnostic testing I isolated it to the "fail-on" power switch. It didn't fail on, and I can see why.



Here's the RadicalRC flag-and-pin switch with the pin OUT (power on). When the pin is pulled, the upper plate (the two wider horizontal tabs in the middle) held up off the lower contacts by the pin (the two smaller vertical tabs on each side of the lower plate) drops down closing the circuit by connecting the upper plate and two small tabs on the lower plate. The connection is in the middle aligned horizontally. Nice and simple! This should fail closed. When the pin is IN (power off) the main circuit is opened because the upper plate is lifted off the tabs opening the circuit, but allowing charging through the Futaba plug on the flag side through a third circuit through the pin. This failed because the upper plate stopped coming down far enough to close on the tabs. Essentially, the U shaped (on its side gap facing us) upper plate didn't spread wide enough anymore to contact the lower plate tabs. The design needs a spring to push it down and hold it down when the pin is out. This spring would go between the sides of the U of the upper plate "holding" the U spread. I wonder if the outside temps and humidity made the metal expand but causing the U to narrow enough lifting the tabs?



Here the pin is in (power off) lifting the upper plate. You can see those horizontal tabs are a smidge up, lifted off the immovable lower side vertical tabs.This is pretty clever for being so simple, and allowing charging through the Futaba connector on the flag pin(not seen)!



The only switch I have on hand to replace it is a dual switch. Singles with a plate and charge lead but nomfuel spot are hard to find. Since I am now using only an electronic remote switch on the reciever for the ignition, I only need one power switch. Since the switch is the most likely failure point, I decided to make it a redundant switch. I soldered the leads in parallel, so if at least one is working the aircraft gets power, but both need to be turned off to cut power. This way if one switch fails the other continues to pass power. I use one 5000 mAh battery pack to power the ignition and the receiver through 6V power regulator.

I plan to replace the flag and pin switch on the Pitts. I am not sure if the hot temps caused the metal of the switch to come off the tabs causing it to fail, but I can't have that happening and no longer trust this switch. I'll make my recommendations to RadicalRC because this switch is otherwise awesome and clever. Its still a great product but needs a fix.




I made this a redundant switch by taking the two "IN" wires that came one from the ignition pack and the other from the reciver pack, and combining them in parallel into one "IN" lead, and the "OUT" wires into one "OUT" lead. The upper pic is the BEFORE though I had already cut the "IN" female Futaba leads off, you can still see the male "OUT" leads before they were combined. The lower pick is after joining the leads. It works great and makes the dual switch useful!


The "new" redundant switch in situ. Takes up more space.


Engine run up. Leaned the low a bit better and was able to get the idle down a bit more. Looking good, hope to maiden soon!

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