With the flight battery disconnected the right alieron itself moves up and down easily with the push of a finger (the servo arm pushed back and forth by the linkage). The left aileron does too, BUT sometimes it gets to up or down and sticks there. Won't budge. When I connect the battery it snaps to centre and responds to transmitter commands as it should. Never noticed a problem while flying this plane, too.
The servos are SPMDSP60 6.0-Gram Super Sub-Micro Digital Prog Servo by Spektrum.
Your servos are fine, some servos have a little more friction in certain spots than others.
BUT it is NOT a good idea to push servos back and forth by hand, they are designed to move with the motor inside them only. Yes many times you can move them without apparent damage, but you may have warped or bent the teeth of a gear inside, then it may fail later.
If you have to move a servo without a radio, the best way is a servo tester, my favorite is a GWS MT-1 it is very useful, I bought it from BP Hobbies.
If you must push it with your fingers, apply the force GENTLY don't try to twist it too quickly, if the servo doesn't want to move STOP, and hook up the radio or tester.
I learned this the hard way about 30 years ago, I stripped a couple of good servos, my friend who had the gears for them could tell I had pushed the servos, by the look of the old gears.
Forget about moving the servos by hand. That is a good way to strip the gears and every servo that is striped this way is your own fault. No servo is made to be turned by hand. As for the servo making noise, that could be the digital servo making noise which is normal or an analog servo with a fresh charge on the battery. Again normal. Not all servos do that, but a good many do. Unless it is really going nuts, it's nothing to worry about. A little noise and movement around center is normal and the cheaper the servo the more it will do it. Binding pushrods can cause that too, so take the pushrod off and see if it does it and if it is just a little bit, don't worry about it. If it is jumping around center and not staying there, then either your not transmitting or you have noise in the system.
Had to swap out a Radian servo at the field yesterday. I had crashed the Radian while slope soaring the previous weekend. Broke it into about 9 pieces. Took about 1.5 hours to get it all back together.
Everything seemed to work OK but I noticed the elevator servos was making some odd sounds. I don't think I fully stripped the gear but the teath were clearly not moving smoothly and I was afraid it would jam.
I had a Hitec HS-81 in my tool box so I swapped it out at the field and had a great flying day. The arms on the 81 are not as long as the Parkzone servo but it worked fine.
The gears may not have stripped, but they could be mashed a little and causing the servo to act funny. They also are not long for this world if you keep flying it like that.
That sounds like one of my crashes and while I don't crash that much, when I do it is normally a good one. I don't do things half way. Glad to hear you got it all back together again and flying. I don't have any foam gliders, so when I pile one in, it is normally a lost cause.
I don't have any luck with HS-81 servos. I ALWAYS strip the gears sooner or later, so I replace them with metal after that and forget about them. I don't know what it is with HS-81 and the HS-55, but I can't seem to keep gears in them. I quite buying the 81 and just buy the 82 now so I don't have to worry about stripping them out. I changed over to the HXT 900 in place of the 55's and they work great.
Analog servos are your lower priced servos. They work well in most sport applications.
Digitals would be my preferred choice for any form of a competition plane or high speed planes. For me their main benefit is more precise centering. They can also tend to hold position better under force, but they will pull a lot of power to do it. If you are flying at 150 mph you don't want those control surfaces being blown back because the servo can't hold position. And in any kind of competition you want those servos to go to the correct center or offset EVERY TIME and hold there solidly. Small variations can be a real issue in competition.
Some brands, like Hitec, have basically the same servo in analog and digital. For example:
Same size, same spline, same ball bearings, same gears, but different controller and maybe a different motor. You can swap one for the other in your plane and they will fit.
Some servos have no bearings. The Hitec HS-55, HS-81 and HS-82MG servos would be good examples. They are very inexpensive but over time they wear and tend to lose their centering ability. But for light duty sport use they are fine. http://www.hitecrcd.com/products/ana...ini/index.html
Today, for sport use, I generally buy servos that have some kind of bearings. These hold center better over time and move more smoothly over time. So a Hitec HS-85 is a little heavier, a bit larger larger and somewhat more expensive than an HS-81 or 82, but if I am putting a new sport plane/glider together I would chose an HS-85 over an 81/82 for the bearings. The HS-45 or 65 have bearings where the HS-55 does not.
In my competition sailplanes is it all digital servos with bearings. I use Hitec, JR and Airtronics digitals. I have to have solid centering in these ships.
I no longer use the HS-81/82 or HS-55 as a servo of choice for new installs in my sport planes. But for a cheap spare to get me through the day an HS-81/82 or HS-55 serves well enough and can cover a wide range of applications. And they do not represent a big investment to just toss in the tool box for unexpected field repairs. If all goes well I will never use them. But they can keep me flying if I need something unexpected at the field, or I can offer them to a friend in need.
I like the HXT-900 for cheap park flyers and the HS-82 I use in slightly bigger fun type planes. They are good low cost servos and work great, even if they don't have that BB in them on the output shaft.
For any kind of serious use, I use a digital. On any big plane I use a digital and that is simply because I don't want to loose one to a stupid servo giving out. True, any servo can go, but the digitals are better all around then analogs are. At least with a digital I don't have to worry about surface blow back and that can be more important then not having that bearing. I do like the twin bearing digitals though, but don't really care to much what brand it is as long as it is a good one and I can get a good deal on it.