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Interesting problem ...input invited

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Old 02-04-2013, 08:28 AM
  #1
flyinwalenda
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Default Interesting problem ...input invited

A control problem recently appeared in my old Sweetstik. I've been flying this for the past several years as my ski plane and never had an issue, old, tough, heavy , reliable plane.
I left it on 72mhz as I have only been flying it in the winter and never had an issue with it. At the field with some other planes on 72 before converting over I would get hit in a certain spot and the hit would be nothing more than a quick wobble and everything would be OK in a split second and it only happened on certain channels. There is a radio tower several miles away and a building about 1500' away with an alam system so I've always contributed one or the other as causing the hits.
Now I've flown it around 5 times this winter on 72 with no issues as normal and one day coming past this area all of a sudden the elevator goes full down and the plane is inverted going away from me at high rate of speed. It took me by surprise and I gave it full down , did an outside loop and got it heading back to me and again it went full down ! I got it back , cut throttle and landed it out in the lower forty...thank goodness there was 8" of snow on the ground!
I took out the 72 reciever and put in a 2.4 reciever on a different radio and checked all of the servos, wiring, etc...and all looked OK. Went out the next time now on 2.4 with a different radio and the same thing happened in the same spot! I got in back and flew in the rest of the way and landed it.
I thought the elevator servo might be failing so I replaced it and took it out yesterday and again it did the same violent maneuver in the same general area and I got it back and landed it.....getting good at this now !
Thinking it might be the battery or a bad servo drawing down the system, I put it on the bench and monitored the voltage on the reciever with all servos being actuated at the same time and the voltage never dropped below 5.8 from a resting voltage of 6.2.
Next I'll monitor the current and see what's happening there.
Interesting problen and if I can't find the issue I'll strip it out and put in different servos and battery.
Here is what's in it:
60 FS nitro, 6volt NiMh pack,Futaba 148 servos in the fuselage, 9201's in the wing , (2) 440 metal rods controlling the rudder and elevator but no metal-to-metal control rod connections between the servo arms and control horns, nyrod on the throttle,only servo extensions are for the wing.
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Old 02-04-2013, 09:08 AM
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Default RE: Interesting problem ...input invited

If you have a metal detector, why not run it over the area where you have been having the "hits". Maybe some some strong metal in the area that is a contributor. Repeat action with a RF modulator/detector.

Interesting problem.
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Old 02-04-2013, 09:33 AM
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Default RE: Interesting problem ...input invited

When all of my planes were on 72 and the hits started it was only on certain channels not every plane was hit and it was the same ones over and over(could have been failing receivers/crystals too). Since then those have been converted over to 2.4 with further no issues and a few other planes I fly still on 72 have no issues. Other flyers at the field experience a hit on certain channels but not others and the hit is again a wobble, sluggish controls, throttle up/down etc but never a violent full deflection movement like this. On this issue no other control is affected, just the elevator . Now that's it's happening with the plane converted over on 2.4 further muddies the water as all of my other 2.4 planes from small foamies to 35 percenters are AOK.
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Old 02-04-2013, 09:38 AM
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Default RE: Interesting problem ...input invited

Could be your Rx switch working intermittently as your symptons sound quite similar to the problem I was having with a defective switch.

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Old 02-04-2013, 07:36 PM
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Default RE: Interesting problem ...input invited

Have other fliers experienced the same issue as you on the same frequency? Iwonder if a pager service in the area, is causing the problem since their operating freq's are not to far off the same range as the 72mHz bands. Also make sure your receiver is sufficiently protected from vibration. A good half inch of foam around the receiver and losely but securely fasten to the air frame is always in good practice. Iuse Velcro bands fastened to the airframe works great for me...

Keep us informed when you finally figure this out...


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Old 02-05-2013, 06:11 AM
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Default RE: Interesting problem ...input invited

Nope. I never had trouble when on 72mhz channel 40 with this plane. Now it's doing it on 2.4 ghz so that leads me to believe it's something inside the plane. Both the 72 and 2.4  receivers are wrapped in foam.

I performed an amp draw test last night and didn't see any irregularities. I guess the next step is to gut it and install different servos, switch, and battery.
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Old 02-05-2013, 05:19 PM
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Default RE: Interesting problem ...input invited

Servo leads might be something to look at. Feedback from other servo's?
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Old 02-06-2013, 12:19 AM
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Default RE: Interesting problem ...input invited

Since this has happened with 2 different receivers on 2 different bands, I would rule out the receiver. You checked the battery but not under engine vibration conditions. I would just replace it and the SWITCH. Not worth chancing it.

Now , I have had 2 aileron servos do what you are describing. Randomly go full deflection and return. I found the problem to be the servo connector on my extension. I replaced it and my problem went away. Both times were in the same plane and the same connector. So, in my case probably an installation issue some where. And , visually, the connectors looked OK.

sp
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Old 02-06-2013, 05:35 AM
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Default RE: Interesting problem ...input invited

It sounds like an intermittent connection somewhere in the wiring and or switches. Get yourself some good electronic contact cleaner and contact lubricant. Take every servo connection apart even into the receiver and spray with the cleaner. Plug and unplug several times repeating the cleaning then use the lubricant and spray the connections and plug back in. If you can spray inside the switch work it back and forth while spraying if not try replacing the switch. If this solves your problem then you have to consider the environment you are flying in is tougher on wiring connections and switches. If this is the problem cleaning may only temporarily remedy the problem. The only sure solution would be replacing everything that has a plug in connection. If you are using NiCad’s you might consider something called black wire syndrome http://xternaldesign.com/blog/index....yndrome?blog=8

Battery packs can be a problem as the tabs are only spot welded in place and the tabs have been known to come off causing intermittent power. It would not hurt to try a different battery pack.

Dennis
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Old 02-08-2013, 04:06 AM
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Default RE: Interesting problem ...input invited

Hi!
Change the Rx battery, a glich nearly always means a bad (lov voltage) battery! And get rid of those steel rods to elev and rudder!
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Old 02-08-2013, 08:02 AM
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Default RE: Interesting problem ...input invited

I could just be a bad servo. Sometimes problems that occur in the same area of the flying site on the same plane are caused by the same vibration freq of the engine in that spot. I had one that would go into fail safe right in front of me over and over again. It was a sport plane and it just so happened the engine would hit a certain spot in the RPM to cause the problem in that area. I would dive down to make a low pass in front of me and it was the only time the engine was turning that much RPM. After a change of the throttle servo the problem went away. This was before the days of 2.4 or I would have tried that.

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Old 02-08-2013, 09:48 PM
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Default RE: Interesting problem ...input invited

Probably tracable to the switch or battery lead.
I had similar problems, glitches, mini hits on a model. But only when inverted.
Couldn't find the answer, kept on flying then lost it during a low inverted. Totalled.
Only after doing a complete wreakage PM did i see that the plastic wire coating had worn away on the battery lead and was shorting out as it moved from upright to inverted.
Increadble to think a loose wire will wear down over time. 
Well they do.
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Old 02-09-2013, 02:09 PM
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Default RE: Interesting problem ...input invited

Has anyone mentioned the gimbal assembly in the transmitter? I've seen alot of manipulation of the flight-pack, with seemingly similar or same results... and it wasn't real clear if the same transmitter was used in each test, or different transmitters.
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Old 02-10-2013, 03:35 PM
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Default RE: Interesting problem ...input invited

It was on 72mhz for 20 some years on my 72 transmitter and then it was converted to 2.4g on a different transmitter.
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Old 02-10-2013, 03:45 PM
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Default RE: Interesting problem ...input invited

Well I could not find anything wrong during my bench testing so......I removed everything from the plane, all of the servos, the switch, the battery pack and the two extensions and replaced everything even the 2.4 receiver got some new padding.
Went out today with hopes of it being fixed but still a bit gunshy of bringing it down in the same spot where this has happened 5 times already.
I flew around high for a few minutes and everything was OK. I came down and approached the area where this has happened before and BANG the elevator goes full down and returns to neutral and AGAIN here I go inverted in the opposite direction.
I push down elevator , got it upright and BAM again it goes down elevator and inverted. I manage to get it upright again and now I'm trying to bring it down and land when BAM again it goes down elevetor inverted about 10' from the ground and now it was was far away from me close to the ground and I magaged to get it upright but there was not enough air space left .

I fixed it good this time.


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Old 02-10-2013, 03:48 PM
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Default RE: Interesting problem ...input invited

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Old 02-10-2013, 03:49 PM
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Old 02-10-2013, 03:57 PM
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Default RE: Interesting problem ...input invited

It went in the snow/ground hard as I just couldn't get it straightened out in time.
The 35 year old epoxy left loose on all of the corners of the fuse and for the most part it was clean breaks with the exception of the landing gear plate, The wing survived so I may put it back together. I built this when I was 17 years old and made the fuselage like a tank !

As far as this problem I am truly stumped and so are the folks who witnessed it the last few times. It was on 72mhz on a 72 radio when it first did it. Converted it over to 2.4g on a different radio and it did it again. Changed out the elevator servo and it did it again. Changed out the throttle servo and it did it again. Changed out everything in the fuse and wing and it did it again.
It must be Aliens ! Maybe I'll call Art Bell !
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Old 02-10-2013, 04:45 PM
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Default RE: Interesting problem ...input invited

I stand by my original post #2. Sorry.
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Old 02-11-2013, 12:48 AM
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Default RE: Interesting problem ...input invited

Now the question is what didn't you change?


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Old 02-11-2013, 01:58 PM
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Default RE: Interesting problem ...input invited


Quote:
ORIGINAL: chuckk2

Now the question is what didn't you change?



List of things I didn't change:
Engine, fuel tank, landing gear, skis, tail wheel, Nyrod going to the throttle, 440 rods to the tail, rods to aileron servos, nylon wing bolts, wood, glue, paint, hinges,nylon horns,and monocoat.

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Old 02-11-2013, 02:21 PM
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Default RE: Interesting problem ...input invited

And I thought that my MW Big Stik 60 at 20 years was old []

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Old 02-19-2013, 02:05 PM
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Default RE: Interesting problem ...input invited

Just a question.....

Are you using EZ Connectors at the Servo ends.. esp. elevators ? (the wire to the EZ connector only)

I had to CA mine when it did that on 72mhz of course they were already set up and had been used some.
When I got home I changed them out and went standard clevis soldered on.

Problem of mine was gone and hasn't come back in over a year.

Cheers

DinD
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Old 04-11-2013, 07:44 PM
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Default RE: Interesting problem ...input invited

Same kind of thing happened with my brother's plane several years ago. He had a 72mhz that also locked up the elevator like yours.  It was before the 2.4 systems came out, but we changed everything else that we could think of and never did get it fixed. I have thought about that problem a few times over the years and also thought that it was the radio, but nowafter reading about how you changed the radio-I am completely stumped.
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Old 04-12-2013, 03:51 AM
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Default RE: Interesting problem ...input invited

It sounds like the problem is finally resolved; at least for this airplane. If you experience this same behavior in another model; try flying the model at a different field and see if the problem persist. I know this sounds strange but over the last 40 years I and others have experienced problematic areas of at least three flying fields I know of. Sometimes the problem has nothing to do with the airplane or gear... Just saying.

Bob
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