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Sep 19, 2020, 02:45 AM
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Curious case of my DX7 G1 blak edition


Hello everyone,
I am competely new and signing up at this forum is quite a 'last resort'.
Most of all I hope AndyKlunz will pitch in.
I have been flying and modeling for more than 30 years and studied and learned quite a lot along the way.

Yes, unfortunately it is a story about a failing radio. I own several radio's by the same brand and have for the past 12 years. I have never ever experienced something like the following.
I have a second hand DX7 G1 black edition. It came with stories of being unreliable en having caused many crashes and loss of aircraft. This was backed up by quite a few clubmembers who where first hand witnesses. The TX had been to a repair center already and the RF deck had been replaced. History showed it did not remedy the problem.
I could not accept that the TX could be the culprit. I used the TX as a my sim TX (I have several more: A DX8 Silver edition - 10+ years old, and recently I bought a new DX8 G2 Blak Edition because of the problems with the DX7, story to follow....).
This summer I was assigned a student. I decided to use the DX7 as it has the wireless trainer option.
I used a the club trainer: Multiplex FunCub, it was fitted with not too bad gear. Turnigy PLUSH ESC with more than capable Amps, Turnigy motor, differten servo's 9gr. And a genuine Spektrum receiver.
All proceded well, binding en binding to the students DX6 G2. The second flight at a mere 150meters out at 40 meters high, there was a full hold and the signal did not recover. Repaired the FunCub and replaced the motor and the ESC and the receiver. A second crash followed and a third and a fourth...
All within distances at no more than 150 meters and 30 to 60 meters high.
I have quite a lot of professional repair skills due to occupation and decided to examine the TX's inside. Found some problems with quality and remedied them. Boards were fitted with high mechanical stress and solder joints were not up to par. I hoped it would be the solution. As long as the FunCub would stay airborn I dediced to use it for testing (without my student). After many many many batteries and different gear in the airpane it showed that up to about 75 meters the problem never ever showed.
Test flights were conducted very carefully and were increasing in distance from the TX every flight as long as things went well. At one time I performed 5 flights in a row, increasing distance and type of flying every time and went almost beyond my visual capabilities on a very clear day. (My vision is quite good). The 6th flight witin a minute and again not very far out a full hold.
I build a test rig, several RX's on a board with a servo attached and the board on a stick. The RX was then walked out at our flying site (flat grass lands) to see at what distance it would fail to pickup the signal. The test was performed with other TX's as well. The DX7 was just as good as the rest, no problem.
The DX7 also never ever failes at a range test.
I then decided to send the TX in with the full story. In the mean time a put together a new testplane (again a foam plane, over here we call them a foamy).
When the TX came back the antenna was replaced and the tech claimed the connector was loose... I can assure you it was not. So.... I test flew.
First flight within 5 minutes the hold occured. I used a proven RX with full preset failsafe capability and so the plane was unharmed.
I put another RX in the plane and even in the living room all the servo's twitch at random intervals but simultaniously. I thought it was just because the TX too close. So I decided to fly the plane like that. The twitching was present in the air, quite anoying, but no hold occurred.
I wrote to HH Germany and the tech proposed to replace the RF deck.
I have studied all I could find about spread spektrum technology, combined with the fact that the RF deck had already been replaced I do not believe it to be the RF deck. Something is wrong upstream of the RF deck, i.e. with the processor board. Some clock is off or something. However I cannot convince the tech that this is the case as he does not have the skills or the equipment to prove it. Nor do I ...
I have also tried for days to reproduce the problem on the ground... I cannot.
I do not know how to test or prove that there is really something wrong with this TX besides the 'normal' things as a burned out RF deck or a loose antenna connector.
Does anyone have any idea how to reproduce the problem on the ground so that it can be repeated to try and pin point the real problem...
Every one thank you very very much in advance... really would like the DX7 to be as reliable as my DX8's.
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Sep 19, 2020, 02:56 AM
Registered User
Give up and use the working DX8 gen 2, it has more features over the DX7.

It was trouble before you even got it from what you said in your story. I’d have given up after the 2nd crash, especially with it already having a bad history.

But, what rx are you using during your tests?

You’re not pointing the tip of the antenna directly at the model at any point during the flight?

And even though it doesn’t sound like a power issue if failsafe is working, but both tx and rx are adequately powered aren’t they?

Start at the simple stuff.
Sep 19, 2020, 05:09 AM
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Thread OP
Thank you for your reply. Yes everything as powered by new cells and the BEC voltage is measured under load and powering very light gear. I have used 5 diffferent RX's in total ranging from 3 original Spektrum RX's, one with sattelite, and my favorite Chines brand (that yielded the glitching) and an orange reciever the last time because it has a descent preset failsafe that saved the model last time. I do also have a AR8010T that came with the new DX8 G2 and I will try that next as it has telemetry...
Sep 19, 2020, 01:33 PM
Registered User
DGrant's Avatar
If it's occurred on more then one Rx, and the DX7 tranny has been serviced and checked out by yourself and a tech, are you sure you're not getting signal shadowing or blocking of signal right in the aircraft itself? There's no mention about your installations, There's components that will hinder/shadow any signal, like batteries, carbon-fiber, and other dense materials, even electronics placed close to a Rx antenna will affect signal.

The 8010T is a great receiver, and that it has telemetry will tell you a story. I suggest using as many remote Rx's as you can. I think you can use up to 3 with the 8010T. The telemetry data will tell you how the signal is performing for each remote Rx, and you'll be able to arrange those for optimum performance. Your telemetry should give you "fades, frame-losses, and holds" with the 8010. At this point it sounds like your telemetry is limited by the Rx you're using... of which there was no mention of any particular Spektrum Rx you've been using.... but a Spektrum Rx equipped with remote Rx's does give a better picture of signal performance, and antenna array and what it's doing.

You seem sharp though, and probably already know much of what I mentioned, but what Rx's are you using and having problems with... since we know about the DX7 already, I'm curious about the model#'s of the Rx's.

I own an DX7 that's been bullet proof, and I fly most of my small glow planes and park-flyers with it. Which is what makes me curious what's going on with your system. I hope you get it worked out though, that stuff can be frustrating no doubt.
Old Sep 19, 2020, 02:14 PM
Esprit Model
A moderator felt this post violated the following rule: Trolling (Provocation). It is temporarily hidden while Esprit Model edits it.
Sep 19, 2020, 09:36 PM
65 years of RC flying
Daedalus66's Avatar
It’s Andy Kunz. And he is very helpful. And no one is better informed about these radios.
Sep 20, 2020, 02:14 AM
Registered User
Thread OP
Thank you for you repsonse. I wil lpost the modelnumbers of the Speltrum RX's. The foamy I am curently using for testing is this one https://www.banggood.com/CESSNA-182-...r_warehouse=CZ . The fuselage offers an enormous amount of space. Never seen by me in an aircraft this small before. RX and antenna placement can be done as optimally as I was ever able to in a model. There are no carbon parts/rods etc. Only a few fibreglass rods. The plane flies very well although it is clearly not F3A capable.
Sep 20, 2020, 02:16 AM
Registered User
Thread OP
I apologize for having Andy's name incorrect. I am impressed with his knowledge. I did think about signal shadowing but why does my other single antenna DX8 not suffer from it. Tried it with the same equipment and never had a glitch.
About pointing the tip of my antenna... Because I too have thought about that, I altered the angle of the plastic housing to be pointing down slightly when I am flying (using a pult). I read that in the end with 2.4Ghz it actually does not really matter much. The repair tech shared that view and replaced the plastic housing including the antenna itself.
I have noticed that during range testing it is noticeable, pointing the antenna to the model or not. However The difference seems not really significant.
Last edited by BWOostdam; Sep 20, 2020 at 02:23 AM.
Sep 20, 2020, 05:59 AM
65 years of RC flying
Daedalus66's Avatar
I’ve never had much of an issue with antenna pointing, but it does make a difference if other things are marginal. So on transmitters with “bendable” antennas, I always set the antenna off to one side and order to minimize the probability of pointing at the model.

Since I went to a DX8G2 about four years ago, and then to a DX9, I haven’t had to think about any of this, as these transmitters have a dual diversity antenna setup which is much less directional.
Sep 20, 2020, 08:19 AM
treefinder
springer's Avatar
A fascinating amount of detective work! I know how you feel when i have a device that I should have trashed ages ago, but still want to find out what is really going on (actually have several scratchbuilt planes line that!) It sounds like you have gone through essentially all the mechanical options. I don't recall anything about the firmware, has that been flashed or updated. I assume the planes have no special features that complicate programming - simplec3-4 ch ? If you continue your detective work I would suggest you throw together a simple plane like a super easy (looks like a paper airplane, takes a couple hrs from sheet to plane ). That will guarantee no plane based issues like shadowing, etc, and since crashes seem to be the only tell, will be repairable at the field. I will follow your journeys! Please continue to update us.
Sep 20, 2020, 11:00 AM
Registered User
Thread OP
@Springer: Thank you for your response.
The link shows the test plane currently in use. It is as simple as can be. Indeed no more than 4 channels and it is a stable, lazy windless evening plane.
The firmware of the TX was updated by me indeed and is the latest. This was a problem free procedure.
Will post as things progress, but the weather over here will not be suitable for quite some time and when I send the TX in again, it will most likely not be returned very quickly. I have had quite lengthy emails with David Buxton who as an quite technical, but very profound explanation on the subject of the workings of RC radios. (https://www.rchelicopterfun.com/RC-Spread-Spectrum.html). We have both concluded from the testing results that: a. furhter testing without a very large amount of money to buy the nescessary equipment would be almost impossible. b. from my current test results and findings it must be, almost without a doubt, a problem with the processor board. But without another DX7-Gen1 I cannot rule it out.
(Another DX7-Gen1 would provide the possibility of swapping out the processor board and see what happens...)
Sep 20, 2020, 12:25 PM
treefinder
springer's Avatar
I guess you are right you have eliminated most everything else! For what it's worth, the plane I was mentioning is this one.: https://www.rcgroups.com/forums/show...E-instructions The fact that everything hangs out in the air would pretty much eliminate issues of in-plane type. On the other hand, if the "brains" are suspect nothing in the plane will help. Gonna set it aside as a parts radio?
Last edited by springer; Sep 20, 2020 at 12:34 PM.
Sep 21, 2020, 12:47 PM
Registered User
Thread OP
@Springer: No I was not planning on setting it aside as a spareparts supply. I am planning on having it repaired. I really do want to know what is wrong with it.

@i_am_mark_evans: The RX's I used: AR610-X, AR600-X, AR6210-X and even an AR6255-X. Other brands : Orange R615X, and a chinese brand I am using very succesfully in my F3A trainer: MKRON series.

And to add to it I must say that the non equal-brand RX's performed slightly up to quite a bit better during testing.
Sep 21, 2020, 01:30 PM
treefinder
springer's Avatar
Relentless! Carry on!
Sep 22, 2020, 08:05 AM
AndyKunz's Avatar
Quote:
Originally Posted by BWOostdam
I have a second hand DX7 G1 black edition.
Sorry I'm late to this thread.

The DX7G1 was gray. It came out about 13 years ago.

Later we had the DX7S. It was silver, like the DX8G1.

Most recently we had the DX7G2. This is the black one. It was replaced by the DX8G2 (also black) which added the diversity transmission.

Quote:
This summer I was assigned a student. I decided to use the DX7 as it has the wireless trainer option. ... All proceded well, binding en binding to the students DX6 G2. The second flight at a mere 150meters out at 40 meters high, there was a full hold and the signal did not recover.
If the DX7 was the student radio and the DX6 was the instructor radio, then the DX7 had nothing to do with the crash. The DX6 was controlling the aircraft. When there is a loss of signal from the student radio, whether by RF or cable, the instructor transmitter announces the fault condition and gives control to the instructor.

It is important that the instructor be attentive to what is going on. The configuration of the training mode is important also - if Master Override is enabled, the instructor needs to keep his fingers off the sticks.

Electrically (electronics, RF, and antenna), a DX6G2 is identical to the DX7G2 you have. The difference is a rotary knob on the DX7. If you have an installation issue in the aircraft, a DX6 and a DX7 would have the same performance.

Are you keeping telemetry log files for your tests? Are you working with the new receivers which provide dBm of the received signals?

Quote:
Does anyone have any idea how to reproduce the problem on the ground so that it can be repeated to try and pin point the real problem...
We have a full-power ground test procedure (attached) that may help you with the test process. While this is written for a problem peculiar to the US DX18G2, the process should help with comprehension of a valid test regime.

Quote:
Originally Posted by BWOostdam
@Springer: No I was not planning on setting it aside as a spareparts supply. I am planning on having it repaired. I really do want to know what is wrong with it.
Then I suggest you send it in for Service to investigate.

Andy


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