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HomeAircraftHelicopterRadio - Servo - Gyro - Gov - Batt › Ratcheting servo- what's that noise?
06-25-2014 01:50 PM  3 years agoPost 1
BOB WHO?

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Downey, Ca.

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I crashed my Goblin 700 Sunday and thought I got off cheap. The only real damage seemed to be blades, linkage rods, and a few minor adjustments that were required. When I installed new main blades and plugged in the heli I heard a clicking in the aileron servo. Although I had checked all servos after the crash and all appeared to be fine, sure enough, I had what seemed to be a bad gear (usually the final output gear). I took the servo (BLS156HV) apart and discovered what I had expected, a bad final output gear. I have spare gears so I replaced this gear and tested the servo on the bench before re-installing it. It behaved like a new servo with full range of motion and no unusual noise. Then after installing it and powering up the bird I heard a weird ratcheting noise when I moved the gimbal from right to left only. So I dissembled the servo again and checked for pieces of the damaged gear the I might have missed. No pieces and no other damage to the other three (3) gears were found. All gears are lubricated and the cases are not cracked. Still when powered up there is a ratcheting sound when moving the stick in one direction only. When not powered up but by moving the servo arm by hand, this same noise is heard from one end of the range of motion to the other in both directions. The gears are fine, all of them. And the servo seems strong when powered up with no slipping or catching just the ratcheting noise. I do not plan to fly the heli with this servo and I do have an extra servo to replace the ratcheting one. I just cannot figure out this noise and would like some ideas. What do you guys think?

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06-25-2014 02:45 PM  3 years agoPost 2
Pistol Pete

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Seffner, FL

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Did you replace all the gears or just the "suspected" one.

If not, you could have one slightly bent or misaligned tooth as such sounds are definitely mechanical and not electrical.

EDited:
If you do replace all gears and it still does it, you could possible have a bent pin.

~~Enjoying the hobby one flight at a time~~

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06-25-2014 05:39 PM  3 years agoPost 3
Chief_USN

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Chesapeake, VA

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I had this happen a couple of years back with one of my 9252's. Brand new set of gears and had a ratcheting sound like you're describing. I swore it wasn't the gears because hey, they're brand new out of the package. After asking a couple of buddies at the field if they had any 9252 gears, I found another set, and low and behold, the ratcheting was gone. After getting home and looking at the gears through a magnify glass, I could see that one or two teeth on one of the gears weren't molded or grooved right and that was causing the ratcheting. To verify, I put the gear in a silent servo and the ratcheting came back. Took that gear out and all was good again. Just because they are new gears, don't rule them out.

Chad

Team HeliProz 12-14
US Navy Chiefs...Unity, Service, & Navigation to the Fleet since 1893

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06-26-2014 02:05 PM  3 years agoPost 4
BOB WHO?

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Downey, Ca.

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No, I have not replaced all the other gears yet. I did not have the other three gears but did order them from Hobbico the same day. I will try that next. It does sound and feel mechanical though. Thanks for that advice as it now makes sense. The likely culprit is the gear next to the output gear...

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06-26-2014 03:37 PM  3 years agoPost 5
Chief_USN

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Chesapeake, VA

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I can't remember which gear it was exactly but it was one with the fine teeth that you can barely see with the naked eye. Not sure what the gears look like in your servo, so take a good look at all of them. Hope you find it.

Chad

Team HeliProz 12-14
US Navy Chiefs...Unity, Service, & Navigation to the Fleet since 1893

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06-27-2014 04:23 AM  3 years agoPost 6
BOB WHO?

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Downey, Ca.

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From my experience in crashing and rebuilding servos (and I've had lots of experience crashing) the final output gear is usually first to go in cyclic servos. I fly metal gear servos, usually Futaba, and they still strip out more often than not in a hard crash. I think the gear that drives the final one might also be more vulnerable than the others. I wish I was not hung up on inverted autos right now, I would save lots of money...

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