Unless you’re replacing your servo with the
same model that came with your car, you’ll
need to consider a few things before you
buy—namely size, torque, gear type, and
SIZE Most 1/10- and 1/8-scale models use stan-
dard servos, with dimensions of approximately
40x36x20mm and mounting holes 47mm apart.
Most manufacturers keep it simple and specify a
servo is “standard size,” or list 1/10 and 1/18 scale
as applications for the servo, so you don’t have to go
looking up dimensions. If you’re replacing a servo in
a mini/micro model or a 1/5-scale car, you may have a
smaller- or larger-than-standard servo. Measure your
old servo and compare dimensions before you buy.
TORQUE More torque = more turning force. Even
inexpensive servos can be very powerful these days,
such as the Hitec HS-645MG shown here. It delivers
133 oz.-in. for less than $35. That’s enough to steer
any 1/10-scale model. Lightweight vehicles, like 2WD
buggies and touring cars, can get away with half as
much torque, but extra torque is never a bad thing.
If you’ve got an 1/8-scale buggy or truck, a steering
servo with 150 oz.-in. of torque or more will give you
the best performance.
SPLINE COUNT The servo’s output shaft (the part
that turns) is splined to fit the servo horn. For the
parts to fit properly, the number of splines on the
horn and the servo must match. Futaba, Traxxas,
and some Hitec servos have 25 splines; some Hitec
servos have 24 splines; and many other brands
have 23 splines. If your servo spline doesn’t match
the horn you want to use, check your car’s manual;
optional horns with different spline counts may be
offered. Or you can just use one of the horns that
came with your servo. Some cars have uniquely
shaped horns, so a factory part must be used.
GEAR TYPE Servo gears are either plastic or metal.
As you would expect, metal wins for durability,
though plastic-gear servos hold up fine in most
1/10-scale models. Go metal-gear in crawlers,
monster trucks, and 4WD vehicles when possible.
As with torque, there’s no such thing as “too much
;ose ridges on the output shaft are called splines, and how many
there are matters.
INSTALL THE SERVO HORN
Switch your radio system and the receiver back on if you switched
them o;. Press the servo horn onto the output shaft. In most cases,
the horn should point straight up, but you may not be able to get it perfectly
straight. No problem, we’ll adjust that at the radio. Secure the servo horn using
the screw supplied with the servo. If you’re installing a servo saver and the
supplied screw is too short, you may be able to use the screw from your old
servo—but only if it has the same size and type of threads as your new servo’s
screw. If they’re di;erent, bring the new servo’s screw and the original screw to
the hobby store, and they’ll help you get the right hardware.
Don’t worry if the horn isn’t perfectly straight—just get as close as you can. Final centering will be
done at the radio.
REASSEMBLE THE RECEIVER BOX
After you make sure the servo is operating as it should, go ahead and
button the receiver box back up. If the box uses a gasket or rubber inserts for
waterproofing, make sure they are properly installed. Consult your owner’s
manual for the specific steps required. All you have to do now is take a test
drive and fine-tune the servo’s center position using the steering-trim dial on
the radio. ✇