JR Servos

[Troy Newman]

The JR 8411SA is an 8411 that has been converted to nylon gears to give a longer gear train life and avoid gear slop. It was originally done by some of the chopper guys to get the extreme power of the 8411 and not loose the tight slopless setup of the 8231's or even the 4131's.

The metal gears are for the high stress loads like the TOC sized models with huge control surfaces and they are moving around huge amounts of weight.

On our pattern models the gear trains don't need to be as robust....and centering and precision is more the top priority...so the 8411SA (Special Application) servo works wonders....

The 8417 and the 9411 are currently not sold by Horizon as SA (Special Application) servos as of yet. They may be in the future. What some of use guys have done is change out the gears in the 9411's and 8417's to a nylon gear set to get the same advantages as the 8411SA.

So when you hear a guy talk about a 8417(SA) he modified the servo by sticking different gears in it. the nylon gears last a very long time as nylon on nylon wears much slower than metal on metal.

There are some applications that need and require the metal gears....In most cases when the servos are brand new there is no difference...after 100-150 flights you may notice some wear on the metal gears. Again this depends on your setup...The Hard Mounted gas motors that bang the heck out of everything...with huge ailerons and rudders tend to need the metal gears and also tend to wear them out as well.

All servos with the metal gears will wear the gear trains faster than the nylon version.

Since our pattern models don't need the metal gears we save some service work down the line.....
For pattern models precision is king....and the need for those robust gears is not seen...In the IMAC models you need in many many cases metal gear servos to keep from stripping out the gear trains with huge ailerons and high 3D rates.

The gears we use:

8411 to 8411SA...Horizon sells a kit to convert them...an 8411SA is about $10 cheaper new.

8417 uses the same kit as the 8411SA but this changes the speed and power of the servo...The 8417 is very fast 0.09sec/60 deg with like 90in-oz of torque....when you change out the gears the servo will change speed slow down a  touch to like 0.11-0.12 and get a little stronger like 99in-oz....

9411 use the 911 gear sets. These are a direct drop in.


I keep the metal output gear that has the servo arm attachment. This makes for a very nice connection on the aluminum servo arms to the servo.

I caution not everybody to change out the gears. It can be tricky unless you know what you are doing.


Troy Newman
Team JR
  ----- Original Message ----- 
  From: Dave Smith 
  To: discussion at nsrca.org 
  Sent: Friday, August 01, 2003 12:12 PM
  Subject: JR Servos


  What is the difference between a JR 8411 and a JR 8411SA?

  Likewise,re the 8417 and the 8417SA?

  TIA,,,,,,,,,,,,,,,Dave
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