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Old 04-15-2007, 09:22 AM
Lance J. is offline
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I've got walley vision
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Iowa City, Iowa
Joined Feb 2007
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Re: DX-7 related crash

I think these types are threads are going to start now that the dx7 has been out. We had a guy that did'nt fly yesterday because his control surfaces were acting irratic and the throttle would not advance on his dx7 system. It would have resulted in a crash for sure, if he'd try to have flown it.
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Old 04-15-2007, 09:24 AM
Lance J. is offline
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I've got walley vision
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Iowa City, Iowa
Joined Feb 2007
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Re: DX-7 related crash

The system worked up to about 75 feet away if he would'nt just happened to go out to about 125ft. he would have flown.
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Old 04-15-2007, 09:35 AM
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Glendale, AZ
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Re: DX-7 related crash

He had an 1100 mah battery. The system worked perfect after the crash. If I wouldn't have been standing with him I would have said he just rolled it into the ground.
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Old 04-15-2007, 10:01 AM
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Re: DX-7 related crash

I have been using DX7 in a glow model and I believe there is an issue with battery current draw and battery voltage level that causes the DX7 with seven channel rx to do weird things. I turned on the airplane to set the throws and had not charged the battery. Just wanted to check servo reverse and initial throw. It was like I had not bound the Rx and the controls started a weird oscillation un commanded movement and nothing responded to the sticks. Just strange as could be.
Charged up the battery pack and everything was rock solid. I have twenty or more flights on the DX7 seven channel rx in that plane now and it is great. I WILL NOT FLY WITH A MARGINAL BATTERY. I believe a marginal battery with flight loads on the surfaces and current draw due to the loads taking the voltage level down is the reason for several DX7 crashes. I go with higher Mah NMh with low internal resistance and recharge when the tester shows half way between toped out and red. Not very scientific but I like the DX7, plan to expand the use in other airplanes, and may go with the module in my 9303. Sorry about the long reply.
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Old 04-15-2007, 10:12 AM
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Its the 4th bell BIOTCH!!!
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Re: DX-7 related crash

Quote:
Originally Posted by greenflier View Post
I have been using DX7 in a glow model and I believe there is an issue with battery current draw and battery voltage level that causes the DX7 with seven channel rx to do weird things. I turned on the airplane to set the throws and had not charged the battery. Just wanted to check servo reverse and initial throw. It was like I had not bound the Rx and the controls started a weird oscillation un commanded movement and nothing responded to the sticks. Just strange as could be.
Charged up the battery pack and everything was rock solid. I have twenty or more flights on the DX7 seven channel rx in that plane now and it is great. I WILL NOT FLY WITH A MARGINAL BATTERY. I believe a marginal battery with flight loads on the surfaces and current draw due to the loads taking the voltage level down is the reason for several DX7 crashes. I go with higher Mah NMh with low internal resistance and recharge when the tester shows half way between toped out and red. Not very scientific but I like the DX7, plan to expand the use in other airplanes, and may go with the module in my 9303. Sorry about the long reply.
Now that i think about it I havent flown any of my spektrum stuff on anything other than 6 volts
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Old 04-15-2007, 10:14 AM
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Re: DX-7 related crash

I think the "ailerons hard over" is a pretty good indicator that it was something in the control chain that somehow screwed up.

Technically, it's also quite possible that this is something that originated in the Transmitter itself. Two receivers with independent CPUs would confirm/deny that. If both Rxes experience exactly the same erratic behaviour at the same time, I'd start looking into the Tx.

The DX-6 is just an add-on to an existing 6 channel radio - not much to go wrong. DX-7 must have new firmware, in order to generate the DSM signal directly. New firmware means possibility of new bugs.

I remember early Futaba 9C Txes doing absolutely unexplained things. I've seen with my own eyes an aileron hard over. Pilot saved the plane. It was sitting on the ground with the aileron deflected. After power cycling the 9C, everything went to normal. Quite similar to your problem.

Maybe it would be a good idea to start using a separate small LiPo(s) to power the receiver, just to eliminate the possibility of voltage drop crashing the receiver software.

Either way, it sucks to lose planes to technology that markets itself as an answer to glitches. I'm sure Spektrum will iron all the bugs out soon.

P.
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Old 04-15-2007, 08:28 PM
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Re: DX-7 related crash

It was a rare perfect near dead calm day in Oklahoma. I put 9 flights on my setup and they were all locked in 100% of the time. I think I figured out what happened to me last weekend:

Last weekend I was flying with the antenna pointed to the side. This is a new feature on the DX7 and is nice to help the radio fit in your field box. Well if you operate a model like this you can fly into the "cone of silence".

I think what happened last weekend was I put in a corrective input to fight a wind gust and the radio locked out at that instant. When the system locks out it holds the last inputs. So the roll continued until I regained signal. The throttle didn't cut because it takes the Rx between 1 and 2 seconds to decide that signal has been lost and cut the throttle.

I verified this on the ground today by running the motor at idle and turning off the Tx to simulate a loss of signal. The flight surfaces all maintain their last position. After a moment the motor will cut out but not instantly.

So I admit that this was a case of User (Me) = Dumb Ass.

Now in your case perhaps something similar happened? Your friend had the antenna in the position pointed straight out towards the field? the airplane is directly in front of him, he put in a corrective input, the radio locks out, the roll continues, the motor keeps running for the short time it takes a model to crash from 8' up.

Bottom line is you want that antenna pointed straight up at the sky when your flying.
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Old 04-15-2007, 09:00 PM
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Re: DX-7 related crash

Now the more I think about this the more sure I am that was what was happening to me. I had the antenna pointed to the left and the lockout in the upline happened on the left.

Also the airplane was super squirly on approach and I remember wondering if the radio was glitching. I don't normally fly that airplane in 15mph winds so I just though it was the conditions. I'm pretty sure I was locking out on approach because I was landing from the left.

Its case closed as far as my situation is concerned. Don't point that antenna at the model.
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Old 04-15-2007, 09:08 PM
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Re: DX-7 related crash

So is it sort of a warm fuzzy feeling that from now on the antenna should be bent to point vertical and not leave it straight out the top of the radio. If you have it vertical surely most of those issues are going to go away or at least be reduced.

You know the antenna looks like a $2 wireless router hand me down. There must be a better antenna that is not so focused if you know what I mean. Something that fires the signal out in some sort of hemispherical pattern.

Just thinking out loud, nothing else.

Kiwi
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Old 04-15-2007, 09:17 PM
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Re: DX-7 related crash

Thanks for posting this thread. I've had bad glitching on AM, FM, and PCM radios. As I'm about to go 2.4 ghz, I'm glad to know that a "glitch proof" system is just false advertising........... Thanks for making my day........


50%



So, what is the point of this post?

(1)Nothing is perfect.
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Last edited by 50%plane; 04-15-2007 at 09:25 PM. Reason: added "point of post"
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Old 04-15-2007, 09:45 PM
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Re: DX-7 related crash

I aplaude all of the early adopters out there who are paving the way with these 2.4Ghz radios.

I will stick to 36mHz a little longer in my $12k superxtra but am following the findings of these 'glitches' in the new technology with interest. I hope you find a definite cause for the odd behaviour of the aircraft and please post it here when you do.
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Old 04-15-2007, 09:51 PM
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Re: DX-7 related crash

Gareth.Ky

I also had an issue with antenna orientation yesterday and figured it out today. Basically I got in a situation on my downwind leg where the antenna was pointing at the airplane. This is a no-no for sure.

The symptom is the plane goes "mushy. " It does not lock out - but it holds position gets a good command, holds position, etc. It makes everything feel like it is in slow motion. Luckily it kept getting enough signal not to failsafe the engine and once I got it to turn to final it locked back in.

Once I figured out what was going on when it happened again today I moved the antenna 1-click and pointing up a little. The problem immediately went away.

If you want to prove this to yourself point the antenna right at the airplane (or even 10deg off) during range check. It will fail - you'll get maybe 30' or 40' range max.

I think the idea of having the antenna 90 deg to the ground is probably right on. It may even be mentioned in the manual(which I plan to check... embarassing I admit)
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Old 04-15-2007, 09:55 PM
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Re: DX-7 related crash

Also - this happens on 72mhz too! Try it in a range check!

Its just that with a long antenna it's actually hard to point right at the airplane. If you use a tray like me and sometimes twist to the side for landings and the like that little antenna points generally at the airplane.
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Old 04-15-2007, 10:28 PM
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Re: DX-7 related crash

I have had the 'mushy' thing once. It was with my first DX6. I BROKE the antenna on that one and did a ghetto wifi antenna replacement. It didn't have nearly the range of the stock antenna. It would get unresponsive and slow and 'mushy' when it was getting out of range.

In theory the antenna replacement should have worked. The Spektrum antennas are indeed standard WiFi antennas. Nothing wrong with that, its a good design with a near perfect spherical radiation pattern. In practice the U.FL connector they use on the boards is really difficult to use without special tools.

There are other omni directional antenna configurations.
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Old 04-16-2007, 12:23 AM
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Re: DX-7 related crash

Quote:
Originally Posted by gareth.ky View Post
Don't point that antenna at the model.
We had a presentation from someone on the new spread spectrum technology at our club meeting this week and one of the things he said was to never point the antennae directly at the plane. I have a 9303 and I've been having problems which I think are due to my set up, which I changed but haven't had a chance to fly the plane. I'm willing to bet things are going to be a lot better and if I was having problems with the plane when it was going up wind in front of me. So I think I was more or less pointing my antenna directly at the receiving wire on the RX which was routed along the bottom of the plane, which is also a no-no. I'm still probably going to go to a spread spectrum system, but I haven't decided to get a module for my 9303 or wait and get the 9303 2.4 system. Need to do some flying this week.
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