Changing Servo Gears And Cases

There are several reasons you might need to overhaul your servos. One of the major reasons is to repair the gears that stripped after a crash. This is especially true for plastic gears, although metal-geared servos strip out on occasion as well. Some crashes will cause the servo case to crack. Even excessive removal and installation of the servos will cause the mounting portion of the servo to break. The rigors of helicopter flight put a tremendous load on servos, which causes the servo gear trains to wear and get sloppy. That doesn't necessarily mean you have to replace the entire servo; a gear train swap is a much more cost-effective way to get your servos nice and tight again. Here's a simple step-by-step for you to use when it comes to tearing apart those electric workhorses and putting them back together again.



1) Remove the servo from your helicopter, then remove the servo horn.


2) Brush off the servo with a clean brush or rag to remove any dirt and debris that might be hanging around.


3) Remove the four screws on the bottom of the servo. These screws hold the entire servo together.


4) Remove the top case, being careful not to lose any gears that might be loose. The top gear that the servo horn attaches to may come out when you remove the top case. This is normal, since the bearing is usually pressed into the case. To remove the gear from the top case, apply light, downward pressure.


5) Using a digital camera, take a quick picture of the servo train just as it is. Make sure the shot is clear so that you can see all the gears. A side angle works best. You might need this for future reference, should you get stuck during reassembly.


6) Remove the gears one at a time. Starting from the top gear working down, separate each gear and place it on a labeled piece of paper in the same order that you're removing them. (See side note.) Do not remove the metal gear that's pressed on to the servo's motor, as it does not come with a new gear set.


7) Next, prep the new gears by applying white lithium grease. This grease will protect the gears and allow them to operate smoothly. Use sparingly. If rebuilding multiple servos for a CCPM setup, be sure the amount of grease used is similar among all three.


8) Match the new gears to the old ones, and install them in the reverse order in which you removed them. The gear sheet will help you along the way.


9) If the case is cracked, this is the time to replace it. Most servos use a single or double ball bearing on the output shaft, which leads us to the next step.


10) Remove the old bearing(s) in the old case and press them into the new case. (The bearing(s) might be stuck to the top gear; if so, remove them and press them onto the new gear.)


11) Inspect the wire leads, making sure that there's no fraying or loose solder joints. If things look suspect, get out the soldering iron and repair.

12) Install the case bottom. Be sure that the servo leads are not being pinched, and also make certain that they're extruding out of the correct point on the case. Then insert and tighten the four screws.

13) Plug the servo into your receiver and make sure the servo is operating smoothly. This is also a good time to place your servo horn back to its centered position.
14) Reinstall your servo, and you're back up and flying. (Unless, of course, you stripped more than one servo. If that's the case, return to step one.)

Use a sheet of paper and label it to simulate your actual servo. Write the words top, bottom, left, and right on the appropriate sides of the paper. When removing the gears, place them in the same order as you're removing them. For example, the top gear with the output shaft towards the right side should go on the top of the page on the right side. The next gear to remove is on the left side of the servo, and would be placed below the top gear on the left side of the page. Picture of the piece of paper with the gears on it.


Conclusion
If you're the type who's intimidated by small moving parts and would rather replace the whole unit, repairing your servos will save you tons of money. This How-To was written to help you overcome that fear and show you how easy it can be. The next time you experience a crash or a servo gear wears out, feel free to dig into that servo and replace those gears.

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