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Spektrum DX-7 Problem ??

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Old 06-15-2007, 07:38 PM
  #1  
acrojack202
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Default Spektrum DX-7 Problem ??

Lost a plane today with a DX-7 radio. Not sure the problem is attributable to the DX-7, but it seems likely to be the source.

The plane is/was an Extreme Flight YAK-55/OS 160 with an AR7000 RX, Hitec 5645MG's on the ailerons and elev (2 ea), a 5985 on the rudder. and an HS225BB on the throttle. All servo's new. The plane had less than 10 flights. Battery is 5-cell NIMH, also new, and was at 6.35 volts under a 1 amp load before flight.

When I first turned the RX on, with the transmitter already on, I noticed the left aileron (AUX 1 on the RX) went to full left deflection, jumped around a bit, then returned to neutral. The right aileron didn't move, at least not noticeably. The elevators moved a little, then assumed the neutral position, so I assumed things were OK. I did a range check, maybe 50-60 ft, all seemed normal.

Shut the system off, fueled and took off. About 5 minutes into the flight, there was an uncommanded momentary roll to the left. Things were then OK for about 30 seconds, then the roll problem appeared again. I set up to land, and on final, an unrecoverable left roll. The plane hit a tree, damaging it severly; perhaps not beyond repair by some standards, but I've written it off.

I placed the wreckage on the workbench and reassembled the control sysem. With the exception of the battery lead having pulled out of the RX, and the the right aileron servo extension pins pulling out of the connector, all looked intact. When I turned the system on, with the transmitter already on, the left aileron jumped around randomly for a few seconds, the locked into the neutral position. After a few moments, it began to move again with no commanded input. It stopped after a few seconds, and servo response again seemed normal. None of the other servos showed this erratic, uncommanded movement, only the left aileron. With the transmitter on and setting on the workbenck, this same action occured several times over the next few minutes - only the left aileron.

I began to suspect a servo problem, so I plugged that servo into the left aileron port of another plane which has a JR955 RX. Steady as a rock. I ran the servo through the servo test program on the JR10X; not a glitch after about ten tests, fast and slow.

I'm not eliminating the servo as the problem (I certainly won't use it again as is), but things do seem to point to the RX. Is there a failure mode where one channel, in this case AUX 1, malfunctions?

In playing around trying to duplicate the problem, I noted that the AR7000 RX would shut down (no light) if the TX antennae came within 6 inches or so of the RX, and was parallel with the RX antennae. If the antennae of the secondary RX were aligned parallel also, both RX's would shutdown and the system would go into failsafe. Is this normal?

Has anyone experienced a similar problem? Comments appreciated.

Jack


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Old 06-15-2007, 10:30 PM
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Default RE: Spektrum DX-7 Problem ??

Regarding RX losing signal in very close proximity - it's normal. Others and myself experience similar when the RX won't pick up the TX if the TX is too close. Move it a foot or so away and all is fine. Apparently the RF section of RX is swamped by too strong a signal.

Regarding RX failure - sounds like symptoms of a poor connection - a lead or a dry solder joint in the RX maybe?


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Old 06-15-2007, 10:37 PM
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Default RE: Spektrum DX-7 Problem ??

G'day Jack,
I would suspect either a servo, or more likely a servo extension lead problem, either where it plugs into the RX or where the extension plugs into the servo lead.
I have hed problems with extension leads, of varying quality, on a variety of receivers, makes no difference what type it is, 2.4Ghz, PCM or PPM, the servo will do all sorts of nasty things if it don't get a good signal or power supply. I had one, where the brown wire pin (negitive) would push out of the connector, as the two ends were pushed together, I didn't notice, so I heat shrinked, & installed, only showed up as a problem when the engine was running, & that was on PCM, with an OS 160FX, the servo jumped around something weird, so I knew it wasn't a radio signal problem, I replaced the servo & ext lead, & the problem went away, I found why when I got home & dsmantled the lead.
Also if the TX is too close to the RX, it is normal to have problems, due to the TX swamping the RX.
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Old 06-16-2007, 07:57 AM
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Default RE: Spektrum DX-7 Problem ??

You did't mention whether or not you set the failsafe during the set up. It's sounds to me that you had a servo problem somewhere. Dennis
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Old 06-16-2007, 08:10 AM
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Default RE: Spektrum DX-7 Problem ??

Jack - First, I offer my condolences; you lost a really good combo, airplane and engine are great performers. Sad to read.
Your troubleshooting, and testing/cycling seems to confirm that the servos are okay. Others have mentioned extensions; I know I've had those go t-ts up just by plugging in. Had one once that would fail only when I tied it together with the dental floss; later found the crimp on that pin defective. Took forever to find that one.

If you have isolated the failure mode to the RX only, I would pursue warranty replacement of that, of course. With an explanation/discussion about the result of the failure. Properly handled, sometimes manufacturers will do "things" to help when approached appropriately.

Sounds like you have good equipment, good testing techniques, and may have just had a bad Rx. Must admit that the symptoms described really had me conclusion-jumping to offer that it must be an extension or connector/pin/crimp. But it seems your testing has disproven those as failure modes.

Let us know what you learn. I'm running AR7000's with my Spektrumized 9303 on all my planes.
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Old 06-16-2007, 05:04 PM
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Default RE: Spektrum DX-7 Problem ??

Thanks for the replies. I haven't reached any conclusions yet; the autopsy is still underway. The servo extensions are all JR heavy duty and all new..... but that doesn't mean they can't be at fault. I haven't checked them individually yet, but that'll be the next step.

Thanks again for the help. I'll let you know what I find.

Jack
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Old 06-16-2007, 06:04 PM
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Default RE: Spektrum DX-7 Problem ??

Jack,

Go back to your testing with the original servos in their original positions. When you find the aileron servo jumping around again just swap the connecters for the aileron and an elevator and see where the problem occurs after the swap. If the aileron is still the one acting up it is either servo or extension. If the problem jumps to the elevator (which is now plugged into the aileron port) you know it is receiver.

Rob
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Old 06-20-2007, 10:38 AM
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Default RE: Spektrum DX-7 Problem ??

Some more test seems to have isolated the problem to the one servo and /or its extensions. Changing ports on the rx (rt ail, elev or rudder) still gives an occasional erratic motion on that servo, but no others. That would seem to point fairly conclusively to the servo.

I have noticed the glitches are more frequent when the battery voltage is high, say over 6.5v open circuit. When the OC voltage is down around 5.7v, the glitches are almost non-existatnt. Don't know if this is significant. I don't believe the problem is with the servo extensions; I have pulled, pushed, twisted, squeezed, even cussed at, every connection and cannot induce the problem - it just occurs randomly, sometimes when you're moving the sticks and sometimes when the transmitter is just sitting there on the bench.

One other thing bothers me - I cannot reproduce the problem when that servo is plugged into another plane with a JR955 RX or an R2000 RX; I've tried both. Even with battery voltage at 6.95v. That's not to say it won't do it, but I've watched it for several 20-30 minute periods and never observed an uncommanded movement. Maybe just coincidence, but I don't believe in coincidences. Does the JR RX's provide some sort of voltage regulation or filtering?

Anyway, that's what I've found to date. Frustrating.

Jack
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Old 06-20-2007, 10:56 AM
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Default RE: Spektrum DX-7 Problem ??

Dirty and/or too many connectors along with high voltage will definitely cause servo jitter or oscillation.

I don't think the jitter is related to the radio or receiver but is servo related.

Bill
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Old 06-20-2007, 12:09 PM
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Default RE: Spektrum DX-7 Problem ??

Aerojack,

Sorry to hear about the loss of such a nice plane. Your ability to reproduce the issue should get you some ear time with HH. If the RX is sensitive to a particular type of servo they might want to hear about that as well. You may have really found something here. Good job. Most wont take the time. Please pursue it to the fullest extent with HH. I believe they will value this type of information.
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Old 06-21-2007, 08:54 PM
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Default RE: Spektrum DX-7 Problem ??

rino,

Are you kidding? You must be. He found a problem with the servo (brand of servo was not mentioned) and you think he should go to HH? Why?
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Old 06-21-2007, 11:54 PM
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Default RE: Spektrum DX-7 Problem ??


ORIGINAL: RobT

rino,

Are you kidding? You must be. He found a problem with the servo (brand of servo was not mentioned) and you think he should go to HH? Why?

Because of this statement

"One other thing bothers me - I cannot reproduce the problem when that servo is plugged into another plane with a JR955 RX or an R2000 RX; I've tried both. Even with battery voltage at 6.95v."
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Old 06-22-2007, 12:03 PM
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Default RE: Spektrum DX-7 Problem ??

Almost comes down to the servo connector. Only change now is the small differences in the different rcvr's pins. I would try changing the connector on the servo, then do another check for all the time it takes.
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