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Rudder servo - 8/5/2012 6:18 AM   
nitro208ca


 

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Status: offline 		I have a problem that i hope that someone can help me with.
The  first thing I have to say is that I'm not a noob to flying. I'm going to try and explain the senerio to you the best that i can.
I own a 1400mm foamy su-26 with a 650kv outrunner motor,50AMP ESC, running a wild scorpion 4s 2800MAH batt.I have flow that plane for about a dozon times and all of a sudden the rudder stopped working.I think the gears in the servo stripped.REplaced the whole servo with a nother one, flew it again about a dozen more times no prob. Tonight I flew it twice with no problem, landed and was about to taxi it over to me to go for another run , when i notice the servo not working the rudder again.All i see the servo doing is trying to move but doesnt, I get a strange grinding sound from it.Now i can easily replace the servo again, but dont want to go through this again after about 12 flights
I would like to know what you guys think the prob is.In the TX program the throw is 100% and everything in the controller has been fine.
Any ideas on what is stripping the gears in the servo?

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RE: Rudder servo - 8/5/2012 6:32 AM   
Charlie P.



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Either binding or vibration most likely.  What brand and model servos are you using?  Is the rudder easy to move with the control rod removed?

Take apart the "dead" servo to see if the gear teeth are missing (new gears are a lot cheaper than new servos).

What is the control arrangement?  Pull-pull?  (Too tight?) 



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RE: Rudder servo - 8/5/2012 6:47 AM   
Mr67Stang



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Status: offline 		If the servo is indeed stripped, I would check to see if the control rod or cables, depending on your set up, is binding anywhere. As asked already, what kind of servo is it. Perhaps, it's not up to the task.

Take the servo and carefully operate it by hand and feel for stripped gears. Are you using a servo extention? Are the pins in the receiver clean and firmly attached? Is it a quality receiver? Are you doing tail touch hovering? High speed snap rolls with nylon gear servos?

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RE: Rudder servo - 8/5/2012 2:02 PM   
JohnBuckner



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Status: offline 		This is all the correct symtoms for flutter. Flutter can and will repeatedly stripe servo gears. It normally can be heard as a high speed buzzing sound during a high speed pass or in a steep dive but on a small foamy may not not be audible.

Was there any buzzing sound during flight just before the rudder stopped working or on the last previous flight?

John

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RE: Rudder servo - 8/5/2012 2:25 PM   
Villa



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Status: offline 		Hi nitro208ca
I had a similar experience. Lost two servos. I had noticed that the servos were getting hot. I finally realized that the rudder was not free to move. I had replaced the vertical stabilizer and rudder, made from foam and tape, with one made from Coroplast. The Coroplast resisted movement. After the two servo failures I corrected the problem by cutting over 50% of the "hinge" surface to free it up. No more problem. Check your rudder to make certain it is free to move.

< Message edited by Villa -- 8/5/2012 6:44 PM >

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RE: Rudder servo - 8/5/2012 2:54 PM   
Rodney



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Status: offline 		Quite obvious that you have stripped the gears in the servo. Could be many causes:stiff hinges, binding push rod, to tight of lines if using pull-pull or positive Ackerman can cause binding with pull-pull setup, to small a servo for the job, etc.

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RE: Rudder servo - 8/5/2012 4:26 PM   
jetmech05


 

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Status: offline 		If you have no binding issues then it would be too small of a servo torque wise.....Out of cursoity what servo are you using?
Isn't the SU-26 twin rudders? 1 servo for both rudders?

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RE: Rudder servo - 8/5/2012 7:47 PM   
nitro208ca


 

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Status: offline 		It is a single servo for the rudder.The elevator is a twin that is conected together with one servo , but that is not the problem. For the humming sound during flight , I never heard anything.I took the servo from my pitts python thinking no problem,THe servo was working while i was in the airand  I noticed it after i landed.My landings are a LITTLE bouncy, but when touching down all wheels touch down at the same time so i dont think it is the landings, if anything the prop will brake.I looked at the control rod and it doesnt seem to be binding.I did have the throw at 125% threw my DX6i, but have changed it to 100%.The servos that i use are the 16gram servo that you get for $18. I'm thinking that they cant handle the 125% throw.I just changed the servo and going out flying , when the batt is charged.I will not really now if it is the 125% thing till i fly it about a dozen times and see what happens

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RE: Rudder servo - 8/6/2012 7:49 PM   
jetmech05


 

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Status: offline 		I think you're problem may be an 18 buck servo.

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RE: Rudder servo - 8/6/2012 8:41 PM   
jaka


 

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Status: offline 		Hi!
100% or 125% has nothing to with if your servo will hold up or not! Why do you belive that?
Check the rudder if it binds and if the rudder trow is enough for the servo so it doesn't have to work at a stop.
What brand servo are you using?

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RE: Rudder servo - 8/6/2012 10:14 PM   
jester_s1


 

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Status: offline 		You've been asked twice already what servo you're running. "$18 servo" is about like telling an auto mechanic, "It's a red car." You really need to figure out why your servos are dying before you fly anymore. Sometimes just going out and hoping for the best turns out fine, and sometimes it's your elevator that dies next.

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RE: Rudder servo - 8/7/2012 1:15 AM   
Gray Beard


 

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Status: offline 		I still have a box full of good $8.99 servos and have never broken the gear train in any of them, I have the black kind.

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RE: Rudder servo - 8/7/2012 1:34 AM   
speedracerntrixie


 

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Status: offline 		Sounds like the servo is running more throw then the rudder can travel. What is happening IMO is that the rudder gets to full mechanical deflection but you have the servo throw set so high that it keeps trying to move the rudder more and finally strips the gears. Think maxing out the steering in your car but still pulling on the wheel.


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RE: Rudder servo - 8/7/2012 2:30 AM   
jester_s1


 

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Status: offline 		Normally a binding servo burns up the motor. Stripped gears are normally the result of a sudden jolt. Think about it- why would a servo manufacturer build a unit that puts out say 48 oz/in of torque, but put in a gear train that can only take 35 oz/in?

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RE: Rudder servo - 8/7/2012 8:25 PM   
nitro208ca


 

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I think i have figured out what the problems is:
It is what most of you were saying. The servo was binding.
I took it out for a flight the other day and after landing i did hear a humming sound with doing  nothing to the controller.I guess you can say its something that i should of caught before but didnt. No worries now, the plane is toast.That same day that i did fly I was on the second batt.Took off and got it to do a vertical torque roll and as it got a good ways up, i suddenly saw two pieces come off the plane. It was atleast 200 feet up, then come down the axact way i was torque rolling up and hit the ground HARD. It turned out that the canopy came off ( some how lost a magnet) and as i was doing the torque roll the batt came out too.The pilot in the plane ejected haha. The plane is not fixable, so will be going out and getting another plane on the weekend.Will be taking the parts from it and re-using some of them



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RE: Rudder servo - 8/7/2012 8:57 PM   
SeamusG



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Status: offline 		Ouch! Sorry to hear ...

Battery came out? Suggest using a couple of lengths of velcro to secure the battery to the tray rather than using the canopy to hold the battery in place.

I've had bad dreams about those little super magnets coming loose so I use left over .5 oz fiberglass cloth across the top of the batteries in "hopes" that it will keep the little things in place yet not keep reduce the "attraction factor" to much.


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RE: Rudder servo - 8/7/2012 11:38 PM   
CGRetired



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Status: offline 		I've told this story a few times, but this is where it really hits home.

One of our club pilots put his planes together somewhat, well, let's say messy. To look in his electronics compartment, you would see a jumble of wires, a battery wrapped in foam and stuffed in anywhere it would fit with no real consideration to how it might interfere with the servos or anything else. The installation was beneath the canope.. the canope was held in place with magnets. The wing was bolted on, then the canope was lifted to gain access to the electronics.

I'm sure you are seeing where this is going.

Well, he set everything up, tested it, and it worked just fine. The battery was fully charged and checked out OK with a loaded voltmeter and there were no obvious binds in the servo linkage.. surprise surprise.. the battery wrap was stuffed in just forward of the servos.

He took off and flew a few orbits. Then he went inverted. I saw something falling out of the plane but was not sure what it was. We were very sure a very short time later when he yelled " I DON't HAVE IT!!" and it crashed to the ground.


We walked over and saw that the canope was missing as was the battery pack. We continued to look around and found both, about 10 feet apart.

Yup.. to quote the above posts, "the battery came out". A very good object lesson for me. Although I spend quite a bit of time making sure there are no binds in linkage, and that nothing will interfere with the linkage, I also secure the battery pack with velcro. My batteries stay put!!!

CGr.

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RE: Rudder servo - 8/8/2012 12:44 AM   
speedracerntrixie


 

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quote:

ORIGINAL: jester_s1

Normally a binding servo burns up the motor. Stripped gears are normally the result of a sudden jolt. Think about it- why would a servo manufacturer build a unit that puts out say 48 oz/in of torque, but put in a gear train that can only take 35 oz/in?


When full stick is applied and the rudder hits it's mechanical stopping point and the servo wants to keep going it is plenty jolt to strip out the gears. Burning out a motor would require that the motor be stalled for a length of time as it takes a bit to build up enough heat to damage the motor. Most servos are designed so that the gears fail before the electronics.



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RE: Rudder servo - 8/8/2012 1:48 AM   
CGRetired



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Status: offline 		Well, we keep saying that the pilot should prepare the aircraft for flight by making sure all linkages are adjusted properly. And, since this is a beginners forum, we will keep saying it.

There are several posts in other threads that discusses the setup process. In fact, there is a link at the top of the Beginners Forum to " www.gettingairborne.com " that has a section that goes into this in detail.

CGr.

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