RCU Forums - View Single Post - Electrical power source requirements for our jets

01-27-2011 | 01:01 PM

#24

JackD

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RE: Electrical power source requirements for our jets

Quote:

ORIGINAL: olnico

Hello guys.
Following a very interesting discussion on this thread, I am opening a discussion on that matter.
http://www.rcuniverse.com/forum/m_10..._2/key_/tm.htm

Jack Diaz has come with a very interesting point about possible causes for a lockout condition:

Quote:

I crashed my L39 in BITW. I could have so easily blame the spektrum system (slow turn to the left, until it hit the ground, no failsafe). However, this is not the way I do things...

My dad and I picked everything up, and spent hours and hours checking and hypothesizing on possible situations (like a dr house diagnose). Luckily, I could check the batteries (they didn't break or explode). I had redundant batteries, and one of them was OK, but the other one was completely drained. My regulators where destroyed

So 2 possible scenarios could have happened:
1) one battery died, and the other one wasn't powerful enough to drive the system
2) I forgot to turn one on.

Further analyzing the crash, the plane crashed just before landing, on a full flap configuration. That points more towards scenario 2. The single battery (it was the 6th flight, one probably I should not have done) was not enough to carry through the whole flight, specially with the added load of the flaps down.

Then, the next thing my dad did was to understand discharge curves of lipos and see how the system reacts to low voltage and high loads. What we discovered (and is documented somewhere in a video on RCU) is that when power gets low the servos stop working (go soft) well before the receiver loses power. That perfectly describes the crash (slow turn, without the turbine shutting down). This is also another important learning. Low voltages will make servos stop working, no matter the brand of the receiver, well before the receiver stops working, it is not brown out what you need to fear, is losing power to the servos.

Net... I learned a lesson (expensive one), improved my power system, added a check point to my procedure, learned that redundancy is only worth it if one system can handle the plane, and hopefuly, won't crash again in the same fashion.

If after the crash I went crying ''spektrum, spektrum....'' (and believe me, for the first hour, that's all I wanted to do...) I would not have changed anything in my behaviour and I would be losing another plane.

I know I will hear 2000 experts after this post saying Im wrong. I don't care... I just want that 2 or 3 good friends (or unknown people) learn something and improve after reading this.

I can give more details of my set up to anyone if you shoot me a pm, don't want to name brands...

Read more: http://www.rcuniverse.com/forum/m_10...#ixzz1CF6LJ3Gi

Thank you for sharing this very pertinent analysis Jack.

I am personally a big fan of parallel A123 2S1p batteries setup. I have used 2 Black and Decker Vx pack ( 1100 mAh ) directly plugged into a micro12 Weatronic receiver for now 5 years ( was a JR receiver before the Weatronic came out ) and have accumulated 600 flights on 3 airframes with this setup with 100 % success.

Oli, thanks a lot for pulling this out from the other thread. I truly believe there are a lot of crashes around that are power related and not really understood since the receiver was still working.
Great discussion!!

I've never considered the A123 route, but for no particular reason, just haven't too much thought behind it. However, not using regulators sounds like a big plus.
My big learning from all this is: Use whatever battery you want, but understand how it works. Learn what the discharge curve is, and how much power you have left.
And the other learning is: Redundancy means two independent systems where each of them is capable of flying your plane in the worst conditions. In my case, my system was redundant on flight 1, but by fight 6, it wasn't.

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