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TYPICAL SERVO SPECS 255

wear out very quickly if the servo is used heavily. A bushing is a one- piece sleeve or collar that
supports the shaft against the casing of the servo.
Metal bushings, typically made from lubricant- impregnated brass (often referred to as
Oilite, a trade name), last longer but add to the cost of the servo. The better servos come
equipped with ball bearings, which provide longest life.
When looking at servos, you’ll often see a notion regarding the bearing type, either bush-
ing or bearing, and whether it’s metal or plastic. You also may see a notation for “Top” or
“Bottom”; this refers to having a bushing or bearing on the top and/or bottom of the output
gear (top and bottom is best), like that shown in Figure 23- 5.

Typical Servo Specs

R/C servo motors enjoy some standardization. This sameness applies primarily to standard-
ized servos, which measure approximately 1.6″ 0.8″ 1.4″. For other servo types the size
varies somewhat among makers, as these are designed for specialized tasks.
Table 23- 1 outlines typical specifications for several types of servos, including dimensions,
weight, torque, and transit time. Of course, except for the size of standard servos, these
specifications can vary according to brand and model. Keep in mind that there are variations
on the standard themes for all R/C servo classes.
A couple of the terms used in the specs require extra discussion.

• As explained in Chapter 21, “Choosing the Right Motor,” the torque of the motor is the
amount of force it exerts. Servos exhibit very high torque thanks to their internal gearing.
• The transit time (also called slew rate) is the approximate time it takes for the servo to
rotate the shaft a certain number of degrees, usually 60°. The faster the transit time, the
faster- acting the servo will be.

G You can calculate equivalent RPM by multiplying the 60° transit time by 6 (to get full 360°
rotation), then dividing the result into 60. For example, if a servo motor has a 60° transit time of
0.20 seconds, that’s one revolution in 1.2 seconds (0.2 6 = 1.2), or 50 RPM (60/1.2 = 50).

Table 23- 1 Typical Servo Specifications

Servo Type Length Width Height Weight Torque Transit Time

Standard 1.6″ 0.8″ 1.4″ 1.3 oz 42 oz- in 0.23 sec/60°
1/4- scale 2.3″ 1.1″ 2.0″ 3.4 oz 130 oz- in 0.21 sec/60°
Mini- micro 0.85″ 0.4″ 0.8″ 0.3 oz 15 oz- in 0.11 sec/60°
Low profile 1.6″ 0.8″ 1.0″ 1.6 oz 60 oz- in 0.16 sec/60°
Sail winch small 1.8″ 1.0″ 1.7″ 2.9 oz 135 oz- in 0.16 sec/60°
1 sec/360°
Sail winch large 2.3″ 1.1″ 2.0″ 3.8 oz 195 oz- in 0.22 sec/60°
1.3 sec/360°

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