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RC Radios, Transmitters, Receivers, Servos, gyros Discussion all about rc radios, transmitters, receivers, servos, etc.

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Old 02-21-2006, 11:33 PM   #1
Jeff Boyd 2
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Default How long should servos last?

I am flying better these days (I carry my lucky rabbits foot with me ), and I have begun to ask myself the question "How long should servos last?". I expect that they won't last for ever, and the thought of losing a airplane to a failed servo is unsettling.

Is there a maintenance program or test procedure recommended? Should we just "life" them and toss 'em after so many flights?

Thanks, Jeff
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Old 02-22-2006, 11:41 AM   #2
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The pre-flight check is the way most people find out servos are having problems. Transmitter on, batt connected. Move the control surfaces through their full range watching for "not" returning to neutral or listening for the servo "hum" which may indicate binding. I have been so excited to get in the air, I didn't pay attention to the pre-flight results and took off. Brings up the old adage, "Takeoffs are optional - landings are mandantory!" The elevator servo would not return to center from the "up" direction. The "down" direction was ok. Got the plane down with only minor landing gear damage. If the servo failure had been in the other direction, the model would have been destroyed!! The servo in question is a futaba s3108 micro and has been in about six planes (and crashed in four). Those little plastic gears don't last forever, I guess. This is the plane it was in. Replaced the servo and hopefully I'll get to fly again today.


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Old 02-22-2006, 10:39 PM   #3
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They last a while,for the most part, I have had gears striped and I have had one act funny(trying to go out) most of the time if you pre check before each flight then you wont have to worry about it, but if your plane starts acting as its getting interference then you might want to check it out. if they hum or move back and forth check them out.

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Old 02-22-2006, 10:50 PM   #4
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Originally Posted by Jeff Boyd 2 View Post
I am flying better these days (I carry my lucky rabbits foot with me ), and I have begun to ask myself the question "How long should servos last?". I expect that they won't last for ever, and the thought of losing a airplane to a failed servo is unsettling.

Is there a maintenance program or test procedure recommended? Should we just "life" them and toss 'em after so many flights?

Thanks, Jeff
Jeff, fixed time replacement is the wisest choice of course, as operate to fail has disastrous consequences.

The only condition based maintenance you could perform would be a torque/speed test and measure the play.

...but no one has quantified what is acceptable degradation...so you could only trend it until one actually failed..then assume the rest follow suit.

i would determine what torque you are applying (in % of max) to the servos in question, and then arrive at a number of flight hours based on that.

problem is, no one published cycles at max torque type data...so it would be fairyl arbitrary at least at first.

Tim.

PS have you received emails from me this week?
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Old 02-22-2006, 10:51 PM   #5
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I thought it was forever. I'm probably wrong but I've been using the same Futaba S48s (I think that's the number) that I've had forever. They even landed in the bay (salt water) once and still worked after being rinsed with fresh water.
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Old 02-23-2006, 12:45 AM   #6
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I'm with watt_the?! We have no real baseline, and how the h~ll you gonna know how hard you have working them. I have not managed to wear any out yet, but I do rebuild them (gearbox) when they are acting questionable after an incident. A repair kit is a fraction of the price of a new servo, and it's not hard to do. I keep a spare kit on hand for every servo I fly.

I believe most servos have sealed brushed motors, at least the ones I have seen are. With that in mind, you should get plenty of warning that the brushes are going away. They should begin to skip and studder a bit, maybe even buzz as flyranger suggests. I agree that a good thorough preflight test is essential. I see a lot of guys that are cozy and just flap the controls quickly, then slam the throttle and blast off. Not a good idea in my book. I run the controls stop-to-stop on high rates slowly and watch for irregularities. You get to know what it should look like after a few tests, then when something fishy is happening, check it out before it's too late.

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Old 02-23-2006, 01:06 AM   #7
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Thanks guys. Good info . . makes sense. I could sense Paranoia coming on ! ! . . lol

“If it takes full power to taxi back . . your landing gear is probably up and locked !
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Old 02-24-2006, 03:22 AM   #8
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I have quite a few servos that are near 20 years old (Futaba S28,S20 and S33) that are still going strong although I must admit to not using them too much these days. In fact I have had only 2 or 3 servo failures other than those damaged in less than perfect landings. I've been in the hobby since the early 70's.

BM
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