Animation with Servos

A servo contains a small motor and gear box that rotates a shaft to a precise location and holds it there. This photo shows a typical servo with its top removed. The position of the shaft is based on a digital signal. Most servos rotate through a 180 degree arc while delivering a good bit of torque. Three wires connect the servo to its controller. Two of the wires
Animation with Servos - schematic

connect to a source of DC power, normally 5 to 6 volts. The other wire to the servo receives pulses from the controller that tell the servo where to position its shaft. In the photo below the red wire goes to the positive terminal of the power supply, the black wire goes to the negative and the white receives the positioning pulses. The control pulses are spaced 20 milliseconds apart and the length of each pulse determines where the servo`s shaft will come to rest. A 1. 5 millisecond pulse will place the shaft in its center position, sometimes referred to as "neutral". A shorter pulse of 1. 25 ms will rotate the shaft 90 degrees to the right while a longer pulse of 1. 75 ms will rotate the shaft 90 degrees to the left. In a model airplane radio control system these pulses are generated by the airplane`s radio receiver. The length of the pulses is determined by the position of the radio control transmitter`s joystick. This video shows a servo with a digital oscilloscope screen in the background. The square wave on the oscilloscope`s screen gives a visual representation of the control pulses. Note that the square wave gets smaller as the servo rotates in a clockwise direction and elongates as the servo rotates counter clockwise. We could use radio control transmitters and receivers to control the servos that we use for animation in our layouts but there is a much simpler, more versatile and less expensive alternative. All we...

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