Servos

Servomechanism - an extensive embodiment of an electric motor for controlling various physical processes

What is a servo (servomechanism)? Servos used in remotely controlled vehicles have standardized dimensions - from micro, through medium and standard, to mega size. Regardless of size, a typical servo design uses the feedback phenomenon, i.e., to a given control signal supplied to the servo, it must respond proportionally, in accordance with the expected result. The servo mechanism is connected to a potentiometer, on whose shaft the T-bar is mounted. Pushers are mounted on the T-bar, through which the drive from the servo is transferred to the target element controlled by it.

Connecting the servo - it's not that difficult!

Most servos use a 3-pin female JST connector with a pin pitch of 2.54 mm. There are three wires connected to the connector - these are: a wire to ground (black or brown), a wire to the power supply positive (red) and a wire for the control signal (usually yellow). The insulation colors of individual servo wires may vary depending on the manufacturer's specifications, but the order in which the wires are placed in the connector is the same. If the length of the servo cable is insufficient, you can use extension cables with compatible connectors.

Servomechanism - Control

The third pin in the servo connector is used to provide a control signal that is intended to set the motor shaft to the desired position. The control signal has a square wave with variable duty cycle (PWM). The PWM signal frequency is standard and is 50 Hz, which means that a single signal period lasts 20 ms. The signal duty cycle in one period ranges from 1 ms to 2 ms. Applying a 1 ms pulse causes the servo shaft to rotate extremely counterclockwise, and for a 2 ms pulse, the servo rotates to the extreme counterclockwise position. In order for the servo shaft to return to the neutral position, a signal with a duty cycle of 1.5 ms must be given to the servo. One of the simplest ways to control a servo is to use one of the PWM hardware channels on the Arduino board. Arduino - servo control becomes very simple thanks to this minicomputer.

Power supply for servomechanisms

Servomechanism - principle of operation and power supply. In remotely controlled vehicles, batteries operate at a rated voltage of most often 4.8 V, and when using larger servos, it will be necessary to use 12.0 V batteries. However, for stationary applications, it will be optimal to use a power supply with an output voltage corresponding to requirements of the servo manufacturer. Regardless of the power supply method chosen, the servo motor draws an increased amount of current as the mechanical load increases. An incorrectly selected servo mechanism, due to providing insufficient torque, may increase energy losses in the power supply system and even contribute to incorrect operation of the controller. Thanks to the appropriate power supply and the Arduino minicomputer, the servo becomes a fully functional device for our projects.

Servos with a full range of rotation angle

A standard servo can rotate the shaft by a maximum of 90° to the left or right. For more complex applications, it is worth using servos with a rotation angle of 360°. Such servos can operate as a regular electric motor with a constant rotational speed. The maximum rotation speed of a servo with a full range of rotation angle is usually 60 rpm. If you need higher speeds for your application, then a better solution would be to use a regular DC electric motor, but for precision tasks it is best to use a stepper motor. Unlike conventional servos, 360° servos are equipped with a small potentiometer that allows the servo to be calibrated to the control signal. For servos with a full range of rotation angle, a pulse with a duty cycle of 1.5 ms will stop the servo motor, and pulses with a longer or shorter duration will cause the servo shaft to rotate clockwise or counterclockwise, respectively.