The output shaft rotates in about half of a circle, or 180 degrees. It has physical stops placed in the gear mechanism to prevent turning beyond these limits to protect the rotational sensor.

The angle (of mechanical rotation) is determined by the width of an electrical pulse that is applied to the control wire. This is a form of pulse width modulation (PWM), however servo position is not defined by the PWM duty cycle (i.e., ON vs OFF time) but only by the width of the pulse. The width of the pulse will determine how far the motor turns. For example, a 1500 us (1.5 ms) pulse will make the motor turn to the 90 degree position (neutral position).

PWM width increasing results in counterclockwise rotation, while PWM width decreasing results in clockwise rotation.

SM-0090 servo motor have three wires: black, red and white.

black = ground (GND, battery negative terminal)
red = servo power (Vservo, battery positive terminal)
white = servo control signal line

Motor
Communication	Pulse-width modulation (PWM)
Operating Voltage range	4.8 - 7.4 V
Speed @ 5V (no load)	0.23 sec/60°
Speed @ 6V (no load)	0.16 sec/60°
Speed @ 7.4V (no load)	0.14 sec/60°
Stall torque @ 6V (locked)	9 kg•cm
Stall torque @ 7.4V (locked)	10 kg•cm
Idle current @ 6V (at stopped)	10 mA
Idle current @ 7.4 V (at stopped)	10 mA
Operating travel	90° ± 10°
Running current @ 6V (at no load)	400 mA
Running current @ 7.4 V (at no load)	500 mA
Stall current @ 6V	2.3 A
Stall current @ 7.4V	2.5 A
PWM width range	800 - 2200 us
Neutral position	1500 ± 50 usec
Clockwise rotation	When PWM width decreasing (eg 1400 -> 1000)
Counter Clockwise rotation	When PWM width increasing (eg 1300 -> 1700)
Centering deviation	≤ 1°
Left & Right travelling Angle deviation	≤ 3°
Limit angle	180° ± 10°
Maximum travel	About 125° (800->2200 usec)
Bearing	Ball Bearing
Gear Material	Metal
Output Gear	25 T/diam. 5.80
Connector wire length	30 cm
Dimensions	40.8 x 20.1 x 38 mm (See drawings)
Weight	57 g