{"id":3034,"date":"2018-05-20T16:26:48","date_gmt":"2018-05-20T20:26:48","guid":{"rendered":"http:\/\/dronebotworkshop.com\/?p=3034"},"modified":"2023-04-12T13:07:25","modified_gmt":"2023-04-12T17:07:25","slug":"servo-motors-with-arduino","status":"publish","type":"post","link":"https:\/\/dronebotworkshop.com\/servo-motors-with-arduino\/","title":{"rendered":"Using Servo Motors with the Arduino"},"content":{"rendered":"\n

\"Download \"Parts<\/a> \"View<\/a> \"Download<\/a><\/p>\n

What is a Servo Motor?<\/span><\/h2>\n

We have built a few projects that have used motors to make things move and along the way we have looked at some of the different types of motors that we can control with our Arduino and Raspberry Pi projects.<\/span><\/p>\n

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We have worked with basic DC motors a few times. We built a couple of robotics projects that are based upon DC motors<\/a> and we also took an extensive look at the H-Bridge Controller<\/a> that is commonly used to regulate the speed and direction of a DC motor with a microcontroller or microcomputer.<\/span><\/p>\n

Another type of motor we\u2019ve worked with is the stepper motor. This type of motor has its shaft driven in discrete steps, allowing for very precise control. They are widely used in printer \u00a0and robotics designs.<\/span><\/p>\n

There is another type of motor that we have used in many of our experiments but have not (yet) taken a detailed look at – the Servo Motor. <\/span><\/p>\n

\"Servo<\/p>\n

A Servo Motor is a low-speed, high-torque motor that comes in a variety of sizes. Unlike the DC and Stepper motors the Servo Motor does not normally spin a full 360 degree rotation. Instead it is limited to a range of 180, 270 or 90 degrees.<\/span><\/p>\n

A control signal is sent to the servo to position the shaft at the desired angle. This arrangement with a single signal makes it simple fo servos to be used in radio and remote controlled designs, as well as with microcontrollers.<\/span><\/p>\n

A servo is perfect if you need to position the rudder on a boat or the elevator on an aeroplane. \u00a0They are really useful in robotic work to position cameras, sensors or robot appendages.<\/span><\/p>\n

Servos can also be used as analog gauges like speedometers and tachometers.<\/span><\/p>\n

Types of Servo Motors<\/span><\/h3>\n

A servo motor is essentially a motor that has an input for a control signal that is used to specify the position of the motor shaft.<\/span><\/p>\n

Servos are used in industry as well as in hobby applications. Industrial servos are often AC motors with digital control inputs that cost hundreds or thousands of dollars.<\/span><\/p>\n

We will NOT be working with industrial servo motors today!<\/span><\/p>\n

Hobbyist servo motors are generally DC motors that can be controlled with either a digital or analog signal. <\/span><\/p>\n

Digital servos are used in applications that require quick responses like the elevator on an aeroplane or the rudder on a helicopter. \u00a0We will NOT be working with these types of motors either, although the hookup and code used to drive them with an Arduino is identical to what we will use for our analog servos.<\/span><\/p>\n

We will be using plain ordinary analog servo motors, the most popular type for hobbyist use. They are inexpensive and easy to obtain. Mounting hardware is also very easy to find as these servos are of a standard set of sizes.<\/span><\/p>\n

It should be noted however that while we won\u2019t be working with digital servo motors today they are really very much like their analog counterparts. They use the same PWM control signals as analog servo motors and can be controlled using the same circuitry and code.<\/span><\/p>\n

Analog Servo Motors<\/span><\/h3>\n

Analog servo motors are inexpensive and available in a variety of sizes and ratings. Perfect when you need a tiny high-torque motor that can be accurately positioned and that won\u2019t break the bank.<\/span><\/p>\n

The \u201canalog\u201d part of the analog servo motor is the control signal. Analog servo motors respond to a Pulse Width Modulation or PWM signal to position their motor shaft.<\/span><\/p>\n

PWM is an ideal control medium. It can be generated by a simple timer circuit or with a microcontroller. It can be sent over a single wire or transmitted on a radio or light beam.<\/span><\/p>\n

The Arduino has a number of PWM capable output pins, making it ideal for controlling servo motors.<\/span><\/p>\n

How do Servos Work?<\/span><\/h2>\n

A servo motor is a motor with a built-in \u201cservomechanism\u201d. <\/span><\/p>\n

The servomechanism uses a sensor to monitor the motor shaft position and a controller to control the motor. It is fed a signal that indicates the position that the shaft should be set to. It then moves the motor into the required position. \u00a0<\/span><\/p>\n

In the analog servo motors we will be working with that control signal is a PWM signal whose pulse width determines the angle the motor shaft is to be positioned at. \u00a0The motor itself is a simple DC motor with a lot of gearing to slow down its speed and to increase its torque.<\/span><\/p>\n

In order to function properly the servo motor needs a sensor that can accurately measure its shaft position. On some industrial and high-end hobby servos this is done using an optical interrupter disc, but in most standard hobby servo motors the sensor is a potentiometer. \u00a0This works well as these servos typically travel 180 to 270 degrees, well within the range of a potentiometer. However the accuracy of potentiometers, especially in low cost servo motors, can affect the overall accuracy of the servomechanism.<\/span><\/p>\n

Continuous Rotation Servo Motors<\/span><\/h3>\n

A standard analog servo motor is constricted in its rotation, usually to 180 or 270 degrees (180 is by far the most common). Its internal gearing provides a high torque power pack in a small and inexpensive package.<\/span><\/p>\n

That combination of small size and large torque also make servos attractive to use as replacements for standard DC motors in the design of small devices like tiny toys and robots. This prompted several people to modify standard analog servos by removing the potentiometer to allow the servo to spin a full 360 degrees.<\/span><\/p>\n

Manufactures got the message and now offer \u201ccontinuous rotation servo motors\u201d, essentially servos with the servomechanism disengaged.<\/span><\/p>\n

In a continuous rotation servo motor the speed and direction of the shaft rotation is controlled by the same PWM signal that is used in a conventional analog servo motor. <\/span><\/p>\n

Having a simple one-wire controls signal and the same physical package as a standard servo motor make continuous rotation servo motors attractive for a number of applications.<\/span><\/p>\n

Servo Motor Control Signals<\/span><\/h2>\n

In order to use analog servo motors you need to understand how to control their operation using PWM. The two varieties, conventional and continuous rotation, use the same timing signals but respond to them slightly differently.<\/span><\/p>\n

Let\u2019s take a look at the PWM signals used in most analog servo motors.<\/span><\/p>\n

Conventional Servo Motor Timing<\/span><\/h3>\n

In a conventional analog servo motor a PWM signal with a period of 20 ms is used to control the motors. A signal of 20 ms has a frequency of 50 Hz.<\/span><\/p>\n

The width of the pulse is varied between 1 and 2 ms to control the motor shaft position.<\/span><\/p>\n

\"Servo<\/p>\n