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HelicopterMain Discussion › Uncommanded Elevator input.
07-09-2008 10:05 AM  9 years agoPost 1
HeliHelge

rrNovice

Norway

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I have had issues with the DX7/ AR7000 in combination with JR8717 servo. I have had 2 incidents in one week involving an uncommanded elevator input. Last week in hoover the heli suddenly made a flip backwards (like the start of an Tic-Toc), but i am not there yet. I landed the heli, checked all the cabels / connections but nothing wrong. I flew another 3 tanks with no problems. Yesterday i was at the field again and after a succesfull first tank,i filled up again, and did my normaly check of the radio controls before takeoff. After i let go of the stick, the elevator servo continued moving for another 2-4 seconds. I tried moving the stick again, and the same happend 2 -3 times. I unplugged the elevator cabel from the reciver, plugged it in again / turned on-off the system, and then every thing worked normaly.?????

What if this happens next time in flight???

Anyone having this problem. Bad connecition in the reciver / radio / servo?? Bad soldering?? Many questions and hopefully many good solutions out there.

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07-09-2008 10:08 AM  9 years agoPost 2
artimus

rrKey Veteran

Buckley WA

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Check all of your connections make sure that no wires are vibrating against the Carbon Fiber Frames your will get chatter if they are.

Fly Hard......Team Viagra

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07-09-2008 10:11 AM  9 years agoPost 3
artimus

rrKey Veteran

Buckley WA

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Switch the plugs around with another servo and see if the trouble follows the servo or if it is a channel on the receiver having the problem.

Fly Hard......Team Viagra

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07-09-2008 12:59 PM  9 years agoPost 4
HeliHelge

rrNovice

Norway

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I tried bending and twisting the leads while giving cyclic and collective inputs, but nothing wrong happens. I also tried to change place on the reciver, switching the aileron and elevator cabel. But again i am not able to make the problem appear. I read somwhere else on the forum that one had problems with the potmeter in the servo?? Is there a potmeter in the servo

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07-09-2008 01:27 PM  9 years agoPost 5
dkshema

rrMaster

Cedar Rapids, IA

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No, there never have been "potmeters" in servos. Potentiometers -- yes, Potmeters, no.

It's often referred to as the "pot" and is a variable resistor that is used to tell the servo where it happens to be positioned. Yes, if the pot is dirty (it has a fixed resistive element and a movable wiper) you can have positioning problems.

Over time due to wear, or due to vibration, there is a small amount of "dirt" that can build up on the element, making contact between the wiper and the element somewhat intermittent. When that happens, the electronics inside the servo have a difficult time determining where the servo happens to be positioned, and you can have centering problems, or over and undershoot of the desired position.

Try getting the questionable servo out of the loop by replacing it with a different servo.

Beside the pot going flaky on you, a second common occurrence inside a servo that can cause erratic movement is a broken wire inside the motor. If one of the motor windings inside the servo breaks (usually due to long-term exposure to vibration), the servo will develop a "dead spot". If the rotation of the motor happens to end up positioning one of the commutator segments associated with the broken winding over one of the brushes, the motor won't move when told to. If you bump the servo a bit, the servo will move again. As long as you're moving back and forth, the servo will seem to be OK as the momentum of the motor armature will usually carry the dead commutator section past the brushes. Vibration or flight loads can also cause the motor to move the dead commutator segment past the brushes and the servo appears erratic.

I've had a couple of motors die this way over the years. In one instance,as I was flying towards me, the heli did several un-commanded loops, in a second heli, it rolled over to the left at hover and right into the ground and I couldn't stop it.

A dirty or bad pot, or a broken motor winding can cause what you're seeing. That would be much more likely than it being a receiver problem.

There's an outside chance you could have a bad pot in your transmitter on the elevator stick. The control sticks also use potentiometers to encode stick position.

Replace the servo first, if the problem persists, the transmitter would be my second choice.

-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz

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07-09-2008 02:28 PM  9 years agoPost 6
QuantumPSI

rrElite Veteran

Atlanta, GA

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subscribed

I'm wondering if similar problems like this will pop up. I'm interested in this setup but gonna let the general public do its thing first.

...now where was I, dh/dt = BS-dx/dt
I will fly you forever... till earth do us part

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07-09-2008 03:12 PM  9 years agoPost 7
helimatt

rrElite Veteran

Lafayette, IN

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I thought I heard about this with Spektrum systems somewhere else- particularly elevator going off on its own, can't remember the cause or the fix, but it wasn't a faulty servo in those cases. Try a search for "elevator" AND "spektrum"...

Of course you could swap out the servo, and see if the problem never returns. This is the difficulty with intermittent malfunctions.

Never, ever, ever, ever give up.

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07-09-2008 03:14 PM  9 years agoPost 8
QuantumPSI

rrElite Veteran

Atlanta, GA

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Come to think of it, a friend of mine had a similar issue but it caused him to crash unfortunately. He was in a hover and the helicopter just backflipped and pile drove itself into the ground. We never figured out what caused it. I'll PM him and see if he'll chime in.

...now where was I, dh/dt = BS-dx/dt
I will fly you forever... till earth do us part

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07-09-2008 04:40 PM  9 years agoPost 9
AirWolfRC

rrProfessor

42½ N, 83½ W

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I had a similar problem once. The collective servo (not eccpm) caused the heli to pump up and down all by itself until it pumped into the ground. It was not Spektrum.

After taking apart the collective servo, I found a bad solder joint where it attached to the circuit board. The intermittent connection caused the pumping. The servo worked fine after re-soldering.

Try replacing the servo and see if the problem re-appears

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07-09-2008 05:05 PM  9 years agoPost 10
blurz28

rrApprentice

usa

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me and one other guy at our field....

are having intermittent uncommanded R aileron movement just like what you are describing. I was waiting for a topic like this to come up to say something because it always seems people come out of the wookwork with all kinds of excuses saying its this or that. I am using 9X 2.4 radio with 8717's with the spectrum regulator. I dont think these are isolated incidents. luckily mine will come and go and has only happened 2-3 times while flying but I have always been able to maintain control. I really just dont want to be flying 6 inches off the deck inverted and it decide to glitch.

3,2,1,...+1,2,3,4,5,6,7,8,9,10,11,12,13,14...

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07-09-2008 05:47 PM  9 years agoPost 11
w.pasman

rrElite Veteran

Netherlands

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Here (Netherlands) they call pots potmeters that's why I (maybe incorrect) use that term.

Question: how is your failsafe set up?

I'm not sure but I guess that some servos may go straight into an extreme position if the wire to (or inside) the receiver is partially broken. It might also be the case that the receiver has a problem.

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07-09-2008 05:52 PM  9 years agoPost 12
gadgetdude

rrApprentice

Northern California

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Guys,
See this thread and ultimately my post:
[url=http://http://www.runryder.com/helicopter/t442048p1/]

I still have not decided what I think it is. It is very frustrating and scary to fly and think this could happen again.

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07-09-2008 06:12 PM  9 years agoPost 13
MrMel

rrProfessor

Gotland

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For me it has been the following:

Servo leads rubbing against CF:
Small servo "jitter" quick movements, short movements, very noticable, but not very far movement.

It only take one little stick of CF to make contact, so it can be hard to see.

Servo going bad:
Longer/Harder movement, of course this can probably be different, but two times I had servo fail where they could move the heli alot, then work again for a good while.
Last time it was my tail servo, all of the sudden, perhaps once every 5 flight it would move the tail 90 degree's, it was scary.

Gone fishing..or hunting..or something
My site: http://heli.dacsa.net - VBar videos and more

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07-10-2008 01:00 AM  9 years agoPost 14
turboomni

rrProfessor

East of the Equator

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Bought an AR7000 RX for my plank. The TX is the X9303 2.4 . I run 2 921 Rx's for 2 heli's and a 6100 in a 450 trex. I have not had one problem with my system at all in close to a year of use. Setting up the AR7000 on the plank I noticed a few tiny glitches on the bench of the left wing servo but no big deal and it went away ,rudder too. Flew it it and it was fine..but thought it glitched but thought it might be the wind ,,i dont know for sure. On final for landing ,airleron kicks the plane over abit and the elevator starts pumping and it went in hard demolishing the new plane. Get to the plane and everything is working fine. Sounds like the same thing right?? I'm just glad it was my plank and my heli. If you have ANY doubts about the 7000 and see ANYTHING out of the ordinary like the tiny glitching or anything else,,I would NOT use the rx in anything you remotely care about. Never mind the safety issue that could result.

Setup is everything, All my heli's can fly far better than I can pilot them

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07-10-2008 01:02 AM  9 years agoPost 15
turboomni

rrProfessor

East of the Equator

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Also my elevstor servo was a JR that was recently sent in for service to replace a bad pot,so that was not an issue.

Setup is everything, All my heli's can fly far better than I can pilot them

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07-10-2008 01:16 AM  9 years agoPost 16
AirWolfRC

rrProfessor

42½ N, 83½ W

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Seems to be a latent problem brewing here with Spektrum.

Do we have to fly with data loggers now ?

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07-10-2008 01:18 AM  9 years agoPost 17
turboomni

rrProfessor

East of the Equator

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Forgot to mention my LHS said he just recently sold a DX7 with the same AR7000 RX and almost lost the plane. barely got it down.

Setup is everything, All my heli's can fly far better than I can pilot them

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07-10-2008 01:38 AM  9 years agoPost 18
Yug

rrMaster

UK. Herts

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Have any of you who've had glitchy type problems when using AR7000s taken the rx apart and inspected the antenna wire and it's soldering ?

With those using 8717s, what kind of cabling have you used ? and what of the battery connectors and cable used ?

Obviously, dodgy pots can be real problem, but so can inferior cabling & connectors. When using servos such as 8717s, they can draw large currents, and if you're using standard Futaba/JR cable and connectors all the way to the battery, then you may well have problems resulting in severe voltage drop. In some cases, this causes brownout in the receivers, but eaually, his could cause servos to exhibit erronious behaviour.

Vegetable rights and Peace

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07-10-2008 02:56 AM  9 years agoPost 19
pinewaves

rrNovice

Freeport, NY - USA

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Check the servo wheels...

The JR 8717's are great servos, but you'll find after a hard landing or auto sometimes the servo will start to strip the teeth inside the servo wheels. It's not something the you would nessacarly notice on the bench, but as it get's worst the problem can manifest durring flight as sudden uncommanded inputs. One big hint the wheels may be slipping is when the heli seems to gradually drift out of trim.

Just something that may be worth a check.

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07-10-2008 03:30 AM  9 years agoPost 20
blurz28

rrApprentice

usa

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not any of those things that have been​mentioned....

on mine. Checked the servo lead. perfect. checked the receiver no noticable issues. I seriously doubt its a power issue seeing how everything else continues to work, and mine are the older receivers that take longer to come back after a power outage. it seems to only happen when rapid up and down collective movements are done. Again everything continues to work its just that the right aileron jumps up and down on its own. I had a spare ar7000 that I put in and rebound it to the trans....time will tell if that was the issue or not.

I did at one time have one of the wires that connects the main antenna to the aux break causing a similar issue so I would not doubt it is the antenna. I needed to send mine in for the quick connect fix anyway.

3,2,1,...+1,2,3,4,5,6,7,8,9,10,11,12,13,14...

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HelicopterMain Discussion › Uncommanded Elevator input.
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