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Old Jul 27, 2011, 03:33 PM
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Joined Jul 2011
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Help!
mCPx: something's fishy. Servo? Electronics? ***SOLVED***

Hi there!

Problems with my mCPx. It worked great for ~50 flights but now it's behaving strangely.

When throttling up, it moved in pulses in a clockwise direction (first video). Hovering thereafter went OK for about 5 sec when all of a sudden it jumped up and crashed. The rear servo had, without my input, gone all the way to the upper limit and had become stuck there.
When starting it up now (after manually returning the rear servo), one can see that the left servo does weird things as well. Also, the blue LED on the 3-in-1 board flashes irregularly but in sync with the servo twitches (2nd video). Possibly, it loses connection to the transmitter.
I've re-bound it to my DX8. Now the blue LED stays solid but the rear servo's standard position is all the way up. Won't move down even with full backward cyclic.

Anyone else experienced something like that? What's the most likely error source? Any suggestions?

Cheers,
Jassel



first video:
mCPx rotating in pulses; electronics error? (0 min 52 sec)


2nd video:
blade mcpx behaving strangely (1 min 34 sec)
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Last edited by Jassel; Aug 08, 2011 at 04:04 PM. Reason: solved the problems
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Old Jul 27, 2011, 04:43 PM
RC Reviews & Tx Setup Guides
Tom Z's Avatar
United States
Joined Sep 2007
3,492 Posts
Looks like you got the servo jitters. Your at the time this can happen (40-50 flights).
This is caused by the servo conductive contact strip (the silver stripe) having black stripe marks on it.


See this thread for information, how to clean them, and what to use.
I am CX2Pilot over there. I posted a lot of information on the
last 3 pages.

Vibration or shakes? CHECK THIS!

http://helifreak.com/showthread.php?t=289666


Tom

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Old Jul 28, 2011, 05:07 AM
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Joined Jul 2011
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Tom,
I actually cleaned the rear servo a few days ago so I don't think it's servo dirt causing this problems. Swapping servo connectors on the 3-in-1 board shows that it's probably the rear servo and not the 3-in-1 that causes the problems. I guess I will replace this bugger with a new one.
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Old Jul 28, 2011, 04:29 PM
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Tom Z's Avatar
United States
Joined Sep 2007
3,492 Posts
Next thing to check. This happened to me after a crash and the servo
was doing what yours is doing. Mine was the ELEV servo.

Open the servo back up and check the wiper arms.
Mine got bent down in the crash and the servo jittered like yours. The finger tension was not tight
enough on the conductive strips to make proper contact.
I bent the arms back up with micro tweezers and it works like new again.
Check that no fingers are bent down or bent crooked.
Also check on the wiper arms is too see if they are worn out.
If all this is OK then sounds like you need a new servo.


This is a picture of a servo with worn fingers and one finger is bent.


Tom

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Old Jul 31, 2011, 06:51 AM
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Joined Jul 2011
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Tom,
thx for your suggestions. I checked the servo and it looked nice and clean with no abnormal bends in the fingers. Anyway, I've replaced it with a new one and the swashplate movements are fine now.
HOWEVER, the problem of the blue LED going off from time to time together with servo movements and different motor noises persists (visible in both videos). I have the suspicion that my mCPX either loses power completely for short periods or that it loses connection to the transmitter.
The battery cable is fine (checked with a multimeter) and the connection between my radio and another heli (mSR) never has any issues. Possibly, the 3-in-1 is to blame after all. Time to go to my dealer / connect Horizon.
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Old Jul 31, 2011, 07:05 AM
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Australia...we live inverted.
Joined May 2008
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Before you replace the 3in1 try a new main motor. I'd say that will fix your loss of bind every second or so.

You could also just unplug the existing motor and see if the blue led stays solid.

Amp
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Old Jul 31, 2011, 12:12 PM
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livonia bob's Avatar
United States, MI, Livonia
Joined Apr 2009
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Quote:
Originally Posted by Jassel View Post
Tom,
thx for your suggestions. I checked the servo and it looked nice and clean with no abnormal bends in the fingers. Anyway, I've replaced it with a new one and the swashplate movements are fine now.
HOWEVER, the problem of the blue LED going off from time to time together with servo movements and different motor noises persists (visible in both videos). I have the suspicion that my mCPX either loses power completely for short periods or that it loses connection to the transmitter.
The battery cable is fine (checked with a multimeter) and the connection between my radio and another heli (mSR) never has any issues. Possibly, the 3-in-1 is to blame after all. Time to go to my dealer / connect Horizon.

I would try replacing the whole battery cable.. Just checking with a multimeter will not show the problem of broken strands of wire causing a low voltage to the RX....
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Old Aug 08, 2011, 04:02 PM
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Joined Jul 2011
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OK, it's flying again Seems it suffered from a combination of problems:

1)
The rear servo needed to be replaced. It looked fine on the outside and the mechanics did as well. I don't know what was wrong with it.

2)
The main motor was worn out. Replaced.

3)
The battery lead had several strands broken ~1 cm from the battery connector. Replaced.

Problems 2) and 3) were causing the loss of power/signal and thus the pulse-wise rotation.

Thank you all for your input!

Cheers!
-Jassel
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Old Aug 08, 2011, 05:01 PM
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tonyastro's Avatar
USA, CA, Monrovia
Joined Jan 2008
2,042 Posts
I've had a problem where the aileron servo would suddenly go full right sending my heli crashing hard. This would happen at about 10 secs from lift off. It was weird to look at! I solved it by switching the aileron and pitch servos. I have no idea why that worked but it did. Wish I took a video of it before fixing it
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Old Aug 09, 2011, 07:55 AM
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scottyvisco's Avatar
Berwick,Victoria,Australia
Joined Dec 2008
221 Posts
I have just had the same intermittent problems with a servo, i finally traced it to the servo motor being worn out and not having enough power to drive the gear-train ,put a new motor on and it works fine again

Cheers Scott
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