How To Fix a Broken Servo

From stripped to saved in 10 steps

Words: Lito Reyes

Whether a car gets its juice from a battery or from nitro, we all depend on at least one servo to make it do what we want. But servos are prone to mechanical failure and will eventually need maintenance. The most common problem is usually a worn-out or stripped gear set. Youíll know that the gears are stripped if the servo doesnít turn or if you hear a crackling sound when you give it radio input. This step-by-step shows you how to change a gear set with minimal frustration.

YOU'LL NEED

> Jewelerís screwdriver or Torx driver, depending on the
    servo

> Replacement gear set

> Silicone grease

> Cotton swabs, small brush

> Motor spray, bearing oil (optional)

ONE

First, remove the servo horn or servo-saver thatís attached to the output shaft (assuming that the servo has already been removed from the vehicle). Thoroughly clean the outside of the case with a brush, and be sure to remove all dirt from the area where the shaft exits the servo case.

Thoroughly clean off the case surrounding the output shaft. You donít want dirt or debris to drop into the gears when you disassemble the servo.


TWO

Remove the four screws that secure the case. If your servo uses Torx screws, get the correct Torx driver; donít hack at the screws with a Phillips tool.

Use the proper-size screwdriver to remove the screws from the servo case; you donít want them to strip out!

 

THREE
Carefully separate the top part of the case from the bottom. Press down on the servo-output shaft while you pull up on the case tabs to allow the gear set to remain intact. Note the tiny shafts on which the gears spin. If there is a rubber seal, care- fully remove it and set it aside.

Left: To split the servo case, apply light pressure to the output shaft with your thumb...


Right:...while you pull up on the case tabs.


FOUR
Carefully separate the top part of the case from the bottom. Press down on the servo-output shaft while you pull up on the case tabs to allow the gear set to remain intact. Note the tiny shafts on which the gears spin. If there is a rubber seal, carefully remove it and set it aside.

Above Left: Hmmm...thereís absolutely no way youíll ever get these gears back on there
the right way...

Above Right:...unless you lay them out in the order you took them off. Then it will be easy.


FIVE
Use cotton swabs to clean out the grease from inside the top case and around the shafts where the gears spin. If any of the gears have chipped teeth, small pieces of plastic may be hidden in that goop, so itís best to clean it all out.

Right: Thoroughly clean the inside of the servo case; look for signs of debris and broken gear teeth.

Left: Inspect all the gears, and look for chipped teeth and stripped sections.


SIX
If your servo has one or more ball bearings for the output gear (the top one with the output shaft), clean those bearings with motor spray and then apply a tiny drop of bearing oil to each. Exposure to motor spray can weaken some servo cases, so itís a good idea to carefully push out the bearing with a screwdriver to avoid getting motor spray on the case.

Left: Clean all bearings and apply a drop of oil to keep them running smoothly.


SEVEN
Use a light bearing oil to lube the near gears. This is especially important on servos with metal gears. You can be generous with the oil, but donít use so much that it will seep out of the case when you put it back together. Also put a drop of oil on each shaft.

Right: Apply a bit of light lubricant to the gear teeth.


EIGHT & NINE
Install the new gear set. Usually, the gear with the output shaft (the top gear) has a notch in it to limit its travel within the top of the case. Look inside the case to check the range, and place the output gear in the center of the range.

Left: Reassemble the servo with the replacement gears, and pay attention to the proper gear arrangement.

Right: Reassemble the servo with the replacement gears, and pay attention to the proper gear arrangement.


TEN
If your servo has a rubber seal, wipe it clean, place it in the seam between the case parts, and then reinstall the screws. Thatís it!

Right: Reinstall the screws, but donít overtighten them. Again, small screw heads can be stripped easily, so donít overdo it!


UPGRADE YOUR SERVO
When itís time to rebuild your servo, you may want to consider an upgrade as well. Many manufacturers offer ball bearings to replace the standard bushing (for more precise centering) or heavy-duty metal gears to replace the stock plastic set. Hitec, for example, offers a complete line of replacement metal gears such as this set shown (item no. 56394 for the HS-525BB servo). Metal gears not only increase a servoís holding power, but they are also considerably more durable than nylon gears. Also, most metal-gear conversion kits usually cost just $17 to $25, which isnít bad when you consider that new metal-gear servos typically cost two to three times that amount.

 

 

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