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Confusing crash probably Futaba RX related (Solution with pics)

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Confusing crash probably Futaba RX related (Solution with pics)

Old 02-11-2009, 01:44 PM
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Default Confusing crash probably Futaba RX related (Solution with pics)

I had a confusing crash which I've posted all about in the beginners forum. They've suggested that I ask here so instead of posting all of it again I'll post the link to the thread. Any help will be appreciated.

[link=http://www.rcuniverse.com/forum/m_8462778/tm.htm]THREAD[/link]
Old 02-11-2009, 01:56 PM
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Default RE: Confusing crash probably Futaba RX related

How many cells are in your RX pack? 4 or 5? What voltage were you reading? Saying that there was "plenty left" means very little.

On the heat related lock outs that have been reported none have recovered as quickly as yours appears to have done so I doubt it is a heat issue.

Looking at your photo of the installation I would re-position one of the antennas into a vertical orientation in your fuse. As they are arranged now while being 90 degrees to each other they are both flat with respect to the surface where you are standing. That is a less than optimal orientation to maintain a link with the TX. The idea with the 90 degrees is to maximize the chances that one of the 2 antennas can be seen by the TX antenna. The way you have them I can see how they might have been blocked by the battery while in the Immelman.
Old 02-11-2009, 02:48 PM
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Default RE: Confusing crash probably Futaba RX related

It's a 4 cell pack. It showed 5.0v under load. I will see how can I get the antennas to be further from the battery and I will try to position one vertically as you said. Thanks a bunch.
Old 02-11-2009, 05:05 PM
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Default RE: Confusing crash probably Futaba RX related

A switch with corroded or dirty contacts, to small a gage wire between the battery and receiver, corroded connectorall possibilities for this type of problem. A good way to check for this is to have a Voltwatch plugged directly into an unused channel on the receiver. If you see the LED's flickering into the yellow/red area when you cycle the sticks, you know you have a power distribution problem; either to small a gage wireing, something drawing excessive current, high impedance battery etc.
Old 02-11-2009, 05:35 PM
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Default RE: Confusing crash probably Futaba RX related


ORIGINAL: plugin

It's a 4 cell pack. It showed 5.0v under load. I will see how can I get the antennas to be further from the battery and I will try to position one vertically as you said. Thanks a bunch.
While not an absolute requirement, Futaba generally suggests using a 5-cell pack with the FASST radios. I suspect you may have hit a low voltage battery failsafe condition. Under load of the servos you may well have had the voltage drop far enough for that to happen regardless of what you tested after the crash.
BTW - what load was on the battery when you read that 5.0 volts.
Old 02-11-2009, 06:17 PM
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Default RE: Confusing crash probably Futaba RX related

The load came from a [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXWDZ5&P=7]Hobbico Expanded Scale Voltmeter[/link] which loads the battery for testing.
Old 02-11-2009, 08:13 PM
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Default RE: Confusing crash probably Futaba RX related

OK. Unfortunately the load that your meter uses is really not sufficient to properly test your packs. From the specs for that meter:

Simulated Load on Receiver side is 225 to 275mA
If you were reading 5 volts with a 225 to 275 mA load I can almost guarantee you that you experienced a low voltage failfsafe event. Four servos moving under the flight loads you were seeing during the mild aerobatics more than likely caused the voltage to drop below the 3.8 volt battery failsafe point. Worse yet if there is any biding on the linkage at the extremes of throw you pull even more amps and drop the voltage even more. I'll bet if you think about it that you dropped your throttle to full low and up again and that regaining control was pretty much coincident with doing that.

I would put a good quality 5-cell NiMH pack in there so you have about the same weight and capacity. Then get a good meter that puts a more real life load on your packs. I teat all my packs at 1 amp load. When I get 5.9 volts on a 6 volt pack I stop flying and charge.

Here's a great source for battery packs: http://www.hangtimes.com
Old 02-11-2009, 08:39 PM
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Default RE: Confusing crash probably Futaba RX related

FASST receivers: (this has been tested before) at 3.7 volts the throttle FS will kick in, still full control of the aircraft, at 2.7 volts the servos will start to get slow, but still you can land, below this you will find yourself in deep trouble.

Doug.
Old 02-11-2009, 09:05 PM
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Default RE: Confusing crash probably Futaba RX related

If it was me I would move the ends away from the servos, they are brushed servos if I am not mistaken.
The brushes if worn may cause excessive sparking under load which may cause RF noise. Random RF noise that close could swamp out the real signal resulting in failsafe, then the servo motors stop moving, the RF noise goes away, signal is now good, regain control. I am not saying this is the problem, just something I would change.
Need more info and debug-testing.


I have tested my 6014's to 3.2v with no problems, fail safe was not set when testing.
All done using calibrated equipment.
There is a reg inside the RX that regulates the input voltage to 3.0v for the RX logic.
Takes quite a dip from 5v to lock every thing out.
Old 02-12-2009, 01:44 AM
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Default RE: Confusing crash probably Futaba RX related

Battery fail safe engages at about 3.8 volts. Your testing was done with it disabled. On a 4.8 volt pack it is not hard under load (possible stalled servo) to get to 3.8.

Good point however about the servos.

I think that the Batt F/S is not the most likely culprit. I think his installation ended up blocking the antennas and perhaps some servo noise or other noise got int and caused a lockout.

Whatever the issue, I am nearly certain that it was not heat related.
Old 02-12-2009, 11:20 AM
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Default RE: Confusing crash probably Futaba RX related

After reading both threads, the one installation detail that got my attention was that the antenna that is positioned across the fuselage is very close to the battery and could very easily be blanked out by it.
I also agree with those who don't think this is a heat related issue, recovery was too fast and the throttle FS kicked in, in the case of a heat issue the receiver goes brain dead until it cools down.
I prefer 5 cell packs and use them exclusively, but am now switching over to 2S 1100mAh A123's for planes this size. With a receiver pack half the size of your current pack you could located the pack in the area under the fuel tank, away from the receiver. I did this on my 4 Star 40 many moons ago, and currently on a 4 Star 60 have a 5 cell Nicd under the tank, the plane tends to build tail heavy anyway
Best of luck,
Pete
Old 02-13-2009, 05:53 PM
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Default RE: Confusing crash probably Futaba RX related

I've re worked all my radio setup on the plane. There's pictures and an explanation at the original thread in the beginners forum. The link is on the first post of this thread. Any comments or suggestions are welcome and greatly appreciated. Thanks.
Old 02-14-2009, 12:08 AM
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Default RE: Confusing crash probably Futaba RX related

i dont like the way you have positioned the RX with the battery behind , this has nothing to do with radio interference but if you should crash this model nose in , say bye bye to the rx as the battery will squash the receiver into the firewall. can,t you position the battery up against the firewall behind tank and then fit the rx behind it and run both antennas parrallel up high to avoid the metal pushrods etc. also the rx switch should be replaced with something better as i think this is the circut board type and they are very deadly due to parts of the board coming adrift [ lose of contact ] when you have all sorted you should do alot of ground tests with engine running above idle whilst you walk away just like range testing.

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