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Old Feb 13, 2002, 03:19 AM
Registered User
San jose, CA
Joined Jun 2000
426 Posts
Why don't my servos keep their neutral point settings?

As I try to make the effort to get out and fly more often I've come to be annoyed by the need to re-center the linkage in most of my planes before I fly. Sometimes I even have to do this again over the time I'm flying a particular model. One time I put together a slope plane where I had parked at the base of a slope, checked everything out, then turned the RX & TX off, and began the trek to the top of the slope. When I got there and turned the TX & RX on, the ailerons were out of adjustment again! The trims were centered the entire time. Across all of my models, the only constant is the TX(JR 652). Could it be sending out different neutral points from one/off cycle to the next? It's not so bad on a two or three servo slope plane, but on a six servo thermal plane it's a pain!

Thank you for taking the time to read this.

Rick
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Old Feb 13, 2002, 08:28 AM
RIP Ric
Andy W's Avatar
Marietta, GA
Joined Jun 1999
43,312 Posts
If you are certain you did not touch the trim settings, something must be wrong with your transmitter, or perhaps the servos (not likely), their installation, or the way you are setting up your linkages. I have never experienced this, once they're set up, they stay that way. I have models I haven't flown in months, I take them off the shelf and fly them and they're trimmed exactly as they were when I first flew them..
..a
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Old Feb 13, 2002, 09:38 AM
Sailplane Nut
NickW's Avatar
Providence, RI
Joined Nov 2000
344 Posts
I have experienced minor trim variations in some of my models from time to time. But these are really minor, and could possibly have something to do with the extreme heat here in florida. When a model goes from my air conditioned appartment to the flying field. But these are rare and are quickly fixed with a touch or two of sub trims. I would follow andy's advice. Start by checking your linkages for slop. A drop of CA in all thread to clevise links, and I also like to put a drop of ca where the pushrod meets the control horn. I let it dry and then crack the CA by moving the pushrod. This takes some of the slop out of the link between servo arm and pushrod. If your linkages are fine then something is up with your radio perhaps.

Good Luck

Nick
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Old Feb 13, 2002, 10:41 AM
Almost a Pilot
Mauilvr's Avatar
NorCal
Joined Oct 2001
3,755 Posts
Based on your description I'd suspect your radio.
Our climate here in the S.F. Bay Area is stabile enough that I think it's safe to rule out any "temperature effects".
CAREFULLY inspect all points of your linkages so you are absolutely certain that nothing mechanical is causing the changes you're seeing.
Once you're sure the linkages are solid the only thing left to suspect is your transmitter.
I'd try many on/off cycles on the bench and try to duplicate the problem. Since you're probably going to have to send it in to Horizon for repair, the more precise of a diagnosis you provide will hopefully yield an effective repair.
It's an unusual problem - good luck!
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Old Feb 13, 2002, 07:19 PM
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St. Mary, Maryland, United States
Joined Dec 1996
8,223 Posts
The lithium backup battery in your Tx may be dead.
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Old Feb 14, 2002, 01:48 AM
Registered User
San jose, CA
Joined Jun 2000
426 Posts
Well, mmm...I am very careful about eliminating mechanical slop, but always make sure the linkages move freely. No use wasting what power your servos produce. I have tried replicating the situation on purpose without any success, although I did discover that not all servos of the same type come out of the box with the same amount of rotation for a given input signal. As far as the lithium backup battery goes, my radio doesn't have trims in memory, just the analog sliders next to the sticks, so not much chance there. I guess I will try calling Horizon and see what they say. Thank you all for your ideas.

Rick
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Old Feb 14, 2002, 11:39 AM
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USA, NY, Jamestown
Joined Jun 2000
2,908 Posts
not centering

I find that my servos do not return to the same center after moving one way versus the other. Is this the same type of problem you are having? This is annoying.
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Old Feb 14, 2002, 11:45 AM
Sailplane Nut
NickW's Avatar
Providence, RI
Joined Nov 2000
344 Posts
Joe, In my experience when a surface has different centering points from different directions, it is almost always a mechanical linkage issue. The usual culprit is that the pushrod is not secured in enough spots in the fuselage, or there is slop in the system somewhere. Turn your radio on and move the surface slightly by hand. How much does it move? You should be able to move it a tiny tiny amount, but it should still hold its neutral position. If you can get it to stay in different spots then something is up!

Good Luck

Nick
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Old Feb 14, 2002, 01:06 PM
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Mark Wood's Avatar
United States, CA, Bear Valley Springs
Joined Feb 2000
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We've found some problems with the plastic control rods such as DuBro in that they sometimes change length with the temperature resulting in having to retrim.

mw
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Old Feb 14, 2002, 07:24 PM
RIP Ric
Andy W's Avatar
Marietta, GA
Joined Jun 1999
43,312 Posts
If your servos are not performing consistantly, you have bad equipment. My servos always come back to the same place if the linkages and hinges are working correctly. In some cases - like my Zagi - where I have a funky control linkage setup, yes, when you return to neutral from 'up' and 'down' deflection, the surface stops in a different location BUT the slightest movement and it is back where it should be, so in flight (or before) there is no trim change needed.
..a
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Old Feb 14, 2002, 08:20 PM
Sweet!
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United States, CO, Longmont
Joined Jul 2001
2,818 Posts
I have noticed that this problem is associated with temperature in my setup. Here in Colorado, big temperature swings occur in the winter. One day, it will be 60, the next day 35. I have been flying the same open class glider for more than a year using virtually the same settings. The long pushrods are stainless steel tubing-rather temperature stable. The short controls are all metal rod and, well, very short. The other day it was unusually cold for me to fly at about 35 degrees. All the gear was cold-soaked in the car overnight. I was surprised to see that virtually all my trims were off significantly ( I have 8 servos aboard). As the temperature increased to about 45 or so, the trims eventually got back to normal. My transmitter is a JR8103 and all the servos are Voltz of one type or other. Knowing something about radios, I don't believe a receiver is capable of causing this much shift (Hitec Superslim). Both the Tx and servos have critical timing circuits that could go somewhat astray if not properly temperature compensated. I have not narrowed down the cause, nor am I likely to do anything about it if I do. I just retrim as needed.

Regards,
Q
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Old Feb 15, 2002, 01:27 AM
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San jose, CA
Joined Jun 2000
426 Posts
I find that my servos do not return to the same center after moving one way versus the other. Is this the same type of problem you are having? This is annoying.

I had this exact same problem with a servo I had in the wing of a Legend. I found through fiddling that if you took off the bottom of the case, and pressed on the PC board just right, it would work fine. Let go, and it would only hit to within 10 degrees of the intended centering point. I tried flying it this way once(I was at the flying field...I DID have the aileron servo on the other wing working properly, so what the heck!)...it was very...'entertaining'. Bottom line, it was a bad servo. The problem I am having now is that they are all doing this in unison, but the variation only happens when you first turn it on. All the servos return to the same center point when you wiggle the sticks around, it's just not the particular center point I set the plane up, or flew last time with.

Mechanical slop is probably not the issue as a 3" long 1/16 dia. music wire rod would never expand or contract more than a few .000" in the mild weather we get in the S.F. Bay Area.

Rick
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Old Feb 15, 2002, 09:05 AM
Dale Lindsay
Mt Airy, Maryland, United States
Joined Sep 2001
653 Posts
My brother had to constantly retrim once. We took the servo apart and the small wiper on the POT that detects center had a small crack it in. The servo would move to the extreme left or right without a problem but when it came back to center, it slowly started to drift. It required him to constantly retrim. We found it just out of curiosity when we tore the servo apart. We took it down to where we could pull the motor and the controller out. Not just the top where the gears are. That's how we found it.

If you're experiencing this on ALL servos, I'd lean more towards the TX. Now, just for kicks, take apart one that you're having to retrim and make sure nothing is cracked.
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Old Feb 16, 2002, 11:34 PM
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San Diego
Joined Oct 2001
36 Posts
Tempest411,

Not sure I understand since I do not know that radio you have but is it a computer radio? My computer radio has mechanical sliders but I assume from what you said that it is not a computer radio.

Anyway, 10 years ago I had the 9 channel Futaba (computer radio) and it worked great for a little while and then it started "wigging out". I would turn off and on the radio and the trims would change each time. It was new so I sent it back for warrenty repair and it was still doing weird things so I threw out an $1100 radio! Still use the receiver though... Out of 12+ radios, this is the only one that has ever changed trims.

David
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Old Feb 17, 2002, 12:11 AM
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Singapore
Joined Nov 2001
802 Posts
I have 2 servos that refused to go back to thier centre positions from after moving one way versus the other too. I figured that there may be some slop in the servo feedback mechanism that is attached to the RVDT( variable resistor) within the servos. So I dismantled the servo gears, put a tiny drop of CA into the servo output gear attachment to the RVDT and solved the problem. I conclude that the problem could be some wear on the attachment after some bad landings or mishandling which back- drives the servos.
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