isabel

I experienced a loss of control using a DX7 & AR7000, reproducible on the ground. I sent in the transmitter and receiver to Horizon Hobby to be inspected. I called them for an update and they said they found nothing wrong, were shipping it back. They say it is probably a low-voltage problem but we tested with 3 sets of battery before sending in for servicing, to ensure that this was definitely not the case. Furthermore we use a powerbox. I am posting the details here in hopes that someone may provide some useful information about this problem. I am hesitant to fly this again, my plane is over 25 pounds, a 35%, I fly in IMAC competitions which are often crowded with competitors and spectators.

Problem description:
While in the air there was loss of signal for a few seconds. The airplane was approximately one hundred and fifty feet away, going on a 45 degree downline. It rolled to a knife edge coming directly at us. Control was regained after several seconds and it was landed. On the ground, the problem was repeatedly reproduced during a range test. The transmitter was held at a distance of about sixty feet from the aircraft and the bind button was depressed while moving the elevator stick. Frequently the following would be observed: control would be lost (the elevator would stop moving), the ailerons would deflect and sometime jitter on their own, and the receiver LED light would flicker or turn off. This would only last for a few seconds. This behavior would occur repeatedly, but in addition, it could be induced without fail by gently jiggling the transmitter. Note that during those ground tests, the engine was not running and we turned off the ignition switch. The antenna was pointing up as recommended. All battery levels were checked and were fine. The transmitter and receiver were turned off and back on, the results were the same.

To me, this seems like a transmitter problem, especially since moving the transmitter around could reproduce the result without fail.

Addtional details:
Previously we could range test to 100 feet with the bind button depressed. There was no one else flying at the field. No known interference problems affecting other DX7 transmitters at this field. All other components have been running fine with a Futaba PCM1024 and 9CAP for a month of daily IMAC practice since this incident occured.

Setup (for Aeroworks Extra 260, 35%):
• DX7 transmitter
• AR7000 receiver
• Emcotec power box, maintains constant voltage to the receiver independently of servo drain
• Two 2600 maH Nickel metal hydrate batteries connected to the power box (we also tested with two different sets of batteries, obtaining the same results).
• 5955 Hitec digital servos all around (7)
• DA-100: 100cc gas engine and ignition

Thank you for any advice or help.

DadsToysBG

My Feedback: (35)

I would suggest that you try the same test without the power box and see if you get the same results. After reading your post I wonder if the power box is working correctly. Just a thought. Dennis

Foamaholic

My Feedback: (1)

You said you jiggled the tx. Maybe check the battery connection on the tx? A friend had the same thing although with a Futaba tx. He found that the tab on the battery connector was preventing it from plugging all the way in so he would often experience loss of signal while in the air.

rmh

• Emcotec power box, maintains constant voltage to the receiver independently of servo drain

I have heard that claim before and for the life of me --I can't see how it can do it.

RobT

My Feedback: (17)

Watching . . .

Eric.Henderson

I have seen loss of signal from a loose fuse as opposed to a loose battery connection. It took a while to diagnose that problem but it was caused by the pilot shaking/trembling as he flew. He was just excited to be flying and then very nervous when he got glitches :-) The fix was to re-tension the fuse-holder clips

I have not been inside a DX7 so I don't know what the fuse situation is like.

If that was happening you should hear a beep or something if the DX7 beeps with on and off switching?

Just theorising.

Regards,

Eric.

Eric.Henderson

I just tried switching my converted 10X on and off and I can get close what you are describing, hmmm.

Also it looks as if it unbinds and then binds. It's a pity that you can't swap in an R9000 for a test.

First, it would eliminate your RX from the equation if you still get the problem.

Second, you can program the R9000 RX to go to a form of failsafe in the event of a lost signal. (the R7000 does not have this functionality). This could tell yo more about what is going on.

Third, if I was flying yor plane I would use the R9000 because it has two receiver "antenna" sockets on the main reciever. The more exposure the merrier with this stuff.

Fourth, if you can borrow another DX7 TX you can bind that one to your airplane, repeat the moving around experiment and quickly detrmine if the TX was the problem.


Regards,

Eric.

isabel

Thanks for the advice so far.

-Regarding switching the emcotec, I am going to try that. I really think it is a transmitter problem since it could be reproduced without fail by jiggling the transmitter, but I will try everything.
-Regarding the loose fuse/battery suggestions. I checked both of these things, and in both cases the symptom would be that the transmitter itself would shut down and "reboot" (as Eric says, the 'beep'). This is not the case in my problem (the transmitter stays on, the receiver light goes off).

I will try to borrow another Tx and Rx to try to narrow it down. Eric, on one hand I am thought about getting the R9000 as you say. For the possibility to plug in a second receiver as you mention, but also you can plug in a Spektrum data recorder (30$) that records the number of fades, fail-safes etc. Would provide me with more info. On the other hand, if the Tx turns out to be the problem as I suspect, it would be a shame to sink more money into this system...

Any other input, please post it...

Eric.Henderson

I had another thought on the way home tonight. The antenna may be loose somewhere in your DX7 the system, giving your results. Some TX modules have had antenna connection issues according to the posts in here there are a few similarities.

And there is more--it was a long ride :-)

If the JR guys are testing in close proximity they may never see the signal loss that you got at 40 feet or whatever your distance was. (Not looking for a war on this statement and I know that there are data that can be gleaned from the RX !)

From what I have seen, if you lose a 2.4 connection at three feet it comes right back. If you lose connection at 30 feet it can take several seconds. If you lose it way out there it could take an eternity as far as you are concerned.

I would love to hear what the final diagnosis turns out to be.

Regards,

Eric.

Ed

Eric, please explain to me how this happens ? Where, and how did you "see" this take place ? Since radio waves travel at the speed of light, why should these short distance's make a difference ? Anyone ?

> Jim

Eric.Henderson

Jim,
I'm not qualified to explain why it happens. All you have to do is try it to see it. (On the ground of course)

I believe this is why the extreme low receiver voltage situation manifests a loss of control the way it does. If you are close up it reconnects quickly but at a 100 yards it is looking for a singal that is weaker by distance etc.

One reason that I personally prefer the R9000 RX is that I can set a form of failsafe during the binding to give the RX time to reconnect with the far away TX in the event of a severe voltage dip.

I have been considering using a capacitor in the voltage supply to see if I could address the random high servo drain. I was going to play with this stuff when I get a data logger etc. so that I did not have to just rely upon visual assements only.

I find these "problems" as interesting as a good mystery novel. Rather than go blasting the suppliers I like to see if I can diagnose the problem, improve the situation/solve the problem or if all else fails provide better data for them to work with.

Regards,

Eric.

isabel

Eric, the loose antenna connection theory really caught my attention... it would fit right in with all the symptoms, really.

I tried to find related posts but couldn't, would you happen to know where those threads are? I'd like to know how the issue was resolved and get any hints on how to determine if this is the problem in my case...

Sidenote, when I called Horizon Hobby / Spektrum for an update, they said they had tested at 100 feet. They also said they had done vibration testing.

Eric.Henderson

I read soooo many forums worldwide and also a few chat lists etc. If I find it I will let you know. I do remember that it was a loose antenna on a TX Spekrum module wire.


Eric.

leyland384

Jim,

There has been some talk about connection issues at very close ranges, and at long ranges. I believe the reason for the long distance connection issue is this:

Spektrum uses multiple receivers and channels to lock onto the transmitter signal. At long distances, the main receiver unit switches around between the internal receiver and the satellite receiver to find the highest quality signal. Now lets say you drop your TX or what ever, and the receiver loses its lock. Now the receiver has to start "looking" for your tx again. If the power was cycled on the Tx, it might come back on two different channels. If your receiver is far away, the signal will be fading in and out between the main and satellite receivers due to the distance and from blockages in the aircraft. The receiver will likely "miss" the transmitter and keep scanning if it happens to be looking on the right frequency, but experiences some fading.

Now, lets tackle the short range link up issue. I believe this is could be caused by overloading of the receiver at very close range. It could be possible that the receiver is scanning, and tries to link up on a channel right next to the one the transmitter is really on. At very close ranges, the signal is very strong, and could confuse the receiver. There is likely a function in the receiver to detect this error, and lock out until power is cycled to try again. (Ever try talking to someone on a CB radio, while another guy is talking on the channel right next to you?)



I didn't design the stuff, so hold the flames. I'm just offering my best "educated guess".

Adam