Campgems

We were talking at the field today and the question came up, how long does a servo last? We are talking about wear out, not damage. It looks like there are two possible failure modes due to wear, the gear train and the pot. How many hours of flying should one expect from a servo today. Say something like a Futaba S3151. Is there any PM (preventive maintance) needed?? I expect that one should expect a few hundred hours of flight time before problems. Even the nylon gears are simular to what you would see in a printer, and they seem to last forever now days. I'm guessing the pots in the current servos are not the old carbon pile type but are ceramic, so they should have a few million actuations before they start to give a problem. Any Ideas?

The Raven

I have a Boomerang 4 trainer with a realistic estimated 300 flying hours using nothing more than Hitec HS-422 servos. I learnt to fly on this plane and have subsequently got to the point of pure abuse on it (full flutter dives) and yet the servos have shown not a single shred of measurable wear (no slop or endplay).

eurekame

Good question, I was just doing some maintenace on my Seagull Edge 540 last night. It uses Futaba 3151's and I noticed all three servos for the tail group have play and 1 elevator servo does not always return to center. I am going to get rebuild kits for the gears and clean them out. They are less than 2 years old and I do not abuse the gear. I estimate less then 150 hrs on the servos. How often should I need to do this? I would also like to hear more on this subject.

Rodney

Metal geared servos wear out the gear train much faster than nylon geared ones do. This is first indicated by slop in the gear train and increased audible noise. The only pots I have ever worn out was on some Futaba S128 but that was only after five years and probably well over 2000 flights on a very large 1.20 sized plane that was severely abused by many less than perfect landings. When they were taken apart, there were grooves worn in the pot resistance element by the pot wipers. They still worked but were erratic on centering.

onewasp

There are so many variables as to make the answer almost impossible.

Taking your lead as the pots or gear train first-----you aren't going to wear out nylon gear trains----IF---- they are capable of handling the forces in you particular A/C.
I switched to metal gears some time ago-----I have gone through a set of pots but not the gear train.

In general terms a two cycle is easier on the "vibes" than is a four cycle (prop acceleration). Now, when we get into soft mounts the equation changes--------BUT based upon the soft mount chosen as they are not all created equal.

Then we have the gassers----two cycle: my experience has been that they are easier on servos than a much smaller four cycle. Matter of fact I have a good friend who has run the same set of 4721's for about six years. No wear apparent in either pots or gear train and this after a slow cycle tester has been used.( this is the same cycler that picked out my worn pots). A 90" is the smallest A/C they have been used in------but each A/C has been powered by a twin.

The twin puts another variable in the equation as they are generally smoother running than a single of the same or similar displacement.

In short---- I don't think you can even come up with an acceptable answer as there are simply too many variables.

I've been through a set of pots in less than fifty flights and then a couple of years with the replacement pots on the same servos----the application? Virtually the same.

MY answer-------kill the "vibes" at the engine and you are as good as it is going to get.
Others will have a different 'take' on it.

Campgems

Thanks for the all the info. Onewasp, could you expand on the "Slow Cycle Tester"? Is this a slower motion than the transmitter servo test (Futaba 9CAP Supper) gives? This sounds as if this is a good preventive maintance test. I'm not sure what you could test for on the gears other than clean them in solevent and the inspect the teeth and then, you wouldn't likely catch a weak tooth.

I have been using the Futaba S3151's mainly because I managed to buy a bunch of them on Ebay for around $12 each. My planes are and were a 40 size trainer, a couple stick types of my design, all running OS 52 four strokes, a Ruperts Dad 3D with a Magnum 70 four stroke and a four star 60 with a Magnum 91 four stroke. I haven't logged enough hours to really worry about wear, but in one crash, I did strip the gears on one servo. I am mostly a sunday driver, the only wild action my planes see is when I get into trouble. I just got the training wheels removed so I may start pressing my luck a bit more. Anyway. the one thing I've noticed with the 3151's is that they have a lot of wink in the gears. I get close to 1/4" aileron travel due to that wink, the linkages show not slop. I though I must have used a couple of the older servos so I put in a new one on one wing yesterday and there is no difference, it is there out of the box. I think I'll look at some analog servos I have and see if they show the same wink, even though they use the same gear set.

The vibes are a concern. The trainer was really bad. At 1/4 throttle, the horizonal stab was moving by about 3/8" on the bench. I use the Dubro vibration mounts, mostly because they take up a lot of the shock when you whack the runway with your prop, which I've done a lot of during training.

I'm of the school of though that says If it ain't broke don't fix it, but if you know it going to break fix it first. It looks like you slow cycle tester is a way to tell that it may be about to break. I've got to find out more on that tester.

Thanks again
Don

onewasp

With plastic gear trains (Nylon or any other) you probably are going to get the gears in one or more servos with a crash. Simply depends on the magnitude.
Metal gears are not going to fail as much as they are going to develop slop. That will be most discernble around neutral (ditto with bad pots) but it is a easily picked up with the slow cycle test.

Not being familiar with the 9C Super or its test function, it sounds as if it may be the same thing. As you can tell from the numbers I have quoted I use JR, 10X but have now switched to Spektrum and sold ALL of my Rx's (50MHz and 72MHz synthesized as well as he Tx itself.
The 10X had an extensive test mode for servos and that was the only thing I missed.


Horizon sells a JR Matchmaker for about $30.00. It has two primary functions 1. It lets you match servos (not program servos that is a Hitec thing) 2. It lets you cycle your servos and you control the cycle rate.
Watching closely you can pick out the servos which show "stepping" ----non linear movement throughout the servo arc. Sticks out like a sore thumb and is generally at and close by neutral. Simply means that the lack of preciseness in the pot is making your flying sloppy.
In Precision Aerobatics the control movements are often quite small (depends on your 'style' but mine results in a multitude of small corrections throughout the flight)------I have flown that way for many, many years so the pots are critical to me.

With the slower cycles, again you are picking the cycle speed from super slow to normal and anything in between, you can listen to the gear train and literally hear a bad tooth (it clicks).
The servo set up is unloaded, plugged into the Matchmaker with a separate battery pack plugged into the Matchmaker for power. You are testing the servo without turning on the Tx or Rx.

I am quite fond of it.

Furthermore it DOES nail the faltering pots and allows a non disassembly appraisal of the gear set. I have found the wear on metal gears to be virtually a non-issue unless you are running massive control surface areas and throws. The inertia of the control surface (amplified by the surfaces weight/area) creates the premature wear.
Often this is so pronounced that you can turn on the Tx/Rx and by hand move the control surface a fair amount as it is in neutral. In other cases look at the control surfaces with the engine during runup and you will see them flailing about when they are supposed to locked in a neutral position.

Simply my preferred methods.
At the sizes you are flying it really shouldn't be much of a problem.

However if you do not balance your props it is an issue ------- a lot bigger issue than you might think.

Campgems

Thanks again for the info. I did a search on cyclers and found a series back in Jan that you were in that gave some links. I also got to playing with my transmitter and it follows the current D/R and end point settings and cycles all servos full throw each way and it takes about 12 seconds for a full cycle. I saw on one of the links that theirs would go down to 45 seconds for a full cycle. Anyway, I played with it a bit on the one plane that I'm flying now and everything seems very smooth. Just the slop in the gears to contend with. I've got a couple sets of gears in the mail now, so I'll swap out the two aileron servo gear sets to see if the tightens things up a bit. That is where my slop is anyway.

I always balance my props, in both end to end and side to side. I've found that the Magnum four strokes have a slight undersize crank shaft size and with some of the wood props, there is as much as 0.010" slop in the prop. I made some shims from 0.005" brass shim stock and am using that to center the prop. It doesn't do much good to balance them if the run off center on the crank. I've got to get around to making some Acetal bushings so I can ream all the props to 3/8" and then have bushings with the ID matched to each engine.

Don

rmh

The Matchmaker is simply one of the most handy tools I have, for setting up models and checking out servos
one problem -- your Futaba servos won't plug directly to it -the little tang is in the way
anyway the servos will probably outlast you -in normal use -
hard landings can strip gears and the nylon parts in a few years -- simply dry out - servo arms especially
- if you can cycle the servos with no shuddering in them - go fly -

onewasp

Amazing coincidence Dick! Your opinion is the same as mine.

Campgems
Dick is the one who recommended the Matchmaker to me when I lamented the loss of my 10X servo test program after switching to Spektrum DX7. Frankly, I like it BETTER than the 10X servo test program as it requires neither the Tx or Rx to be used. BTW take a long look at the DX7------I've been around this Hobby for a l-o-n-g time and I like it the best of any set up yet-------and that includes a whole raft of "Super Radios".

Thanks again Dick.