Thread: Discussion Servo gear failures
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Old Nov 22, 2010, 07:29 PM
A.T. is offline
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MG Servos - Why one Plastic gear in train & Extend Life

Originally Posted by Daemon View Post
Alan, he's not talking about the first gear away from the motor, but the last one that drives the output shaft.
And yes, that is usually the one that fails, but I've seen several other gears fail as well. HS*125's/JRDS168's for instance were notorious for stripping the output gear itself.
If they made that last gear stronger, then some other would always strip. I've generally found that if you make them *all* too strong to strip, then the weak point becomes
the ends of the gear shaft pins, that tear through the case, or the output bearing.. etc.
Or on my bulletproof Volz Micromaxx XPs, the splines on the servo arm strip out and so forth. ian
Misread OP. Unfortunately "101 on servo" previous post
Originally Posted by A.T. View Post
"99% of metal gear servos will have 1 nylon or hybrid gear across all servo manufacturers.
This is normally the 1st gear off the motor as it see's the least load. This is done to minimize any noise feed back from the metal on metal gears to the receiver"

The first gear for an HS-85 is very small and would add a significant cost to make a hybrid, if at all possible for something so small, as used on the larger servos.
101 - Servo FAQ & picking the right servo for the job
Majority of the Hitec primary 1st gears are readily available, even those for HS-85MG were held at LHS but currently O/S.
However, more are on order, refer answer similar thread on manufacturer's forum.
Meantime, it is almost as cheap to buy the HS-85BB+ plastic gear set #56365 and use the primary gear from that for your HS-85MG servo & in need, #56403 for the 81.
Alan T.
Still applies as the smaller the MG servos, the faster the wear on the gears which is much faster than the weaker nylon gear trains.

• Slop or wear in the geartrain - Metal geartrains will wear at a greater rate than resin or plastic gear sets.
Normal use will result in increased gear lash or "slop" over an extended period of time. "
Slop accentuates sudden backlash from hard arrivals and like any metal, something will eventually snap.

To extend gear train life, turn the middle gears regularily upto 180 degrees and relubricate with Servo Grease
so as to have even wear and reduce chance of breakage.
MG servos, irrespective of brand brought in for service, for which gears are no longer available,
have often been put back into use by removing and replacing one or more gears at 180 degrees to
original position in train, so as to mesh unworn teeth, as above.

When servicing gear sets, check the holes into which the pinions fit, case top & bottom, as
often the holes have expanded allowing movement/slop in train which leads to gear teeth lock up
and burn outof servo. A new case set is frequently required.

Do Not Use RED Loctite on MG Servo Screws..
(Hitec RCD supply a star washer which negates screw slippage)
RED loctite, the color of the fluid not the bottle, is a PERMANENT Loctite
and should only be used on components that you are not planning to remove.
. BLUE "loctite" aka Threadlok is a fluid or cream, and is removable.
It will harden up after awhile and prevent the bolt or screw from coming apart from vibration.
Never let either get into contact with plastics, including Karbonite, as the plastic soon becomes soft & fails.

. Servo - DIY Repair - Lubrication (servo grease)

. Servo - Horn arm Spline Count and Inter Brand Compatibility

. Servo - Installation - Correct Mounting & Tips for longer life. with pictures

Readers will be pleased that gear woes are being rectified - look for the new Hitec servos with AGTT gear sets e.g
HS-45HB also HS-5045 digital version.
(new HV (High Voltage 6.0-8.4v) servos are also hitting the shelves)

Alan T.
Alan's Hobby, Model & RC FAQ Web Links
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