4. Advanced Applications of Arduino I/O Servo Motor Control

Transcription

1 EMT Advanced Applications of Arduino I/O Servo Motor Control Dr. Xiaohai Li Dept. of Computer Eng. Tech New York City College of Technology Last update: Spring 2014

2 Copyright Notice The slides here include pictures, figures, diagrams, tables and other contents from a variety of sources. Use them for educational purpose ONLY. Copyrights are reserved by their original authors and/or publishers. Copyright of all other contents is reserved. EMT2461 Dr. Li 2

3 Learning Objectives Understand the internal structure of a DC servo motor Understand the general principle to control a DC servo motor s position Know how to use Arduino to control a DC servo motor (Position control) EMT2461 Dr. Li 3

4 Outline of Contents Internal Structure of DC Servo Motors Position Control of a DC Servo Motor Speed Control of a Continuous Rotation Servo Motor (optional topic) EMT2461 Dr. Li 4

5 DC Servo Motor EMT2461 Dr. Li 5

6 DC Servo Motor Are they the same? The difference btwn servo motor and regular DC brushed motor with gear head? How to identify? Ans: Check the pins! EMT2461 Dr. Li 6

7 Internal Structure of DC Servo Motor Before we reveal the internal structure of a DC servo motor, let us find out how it works. i.e., how to control its position? Ans: The pulse width of control signal determines the angle it rotates! 1ms: 0 ; 1.5ms: 90 ; 2ms: 180 ; 1.75ms:?? EMT2461 Dr. Li 7

8 Internal Structure of DC Servo Motor Again: How a servo motor works? Ans: Pulse width determines the rotation angle. EMT2461 Dr. Li 8

9 Internal Structure of DC Servo Motor Again: How a servo motor works? Ans: Pulse width determines the rotation angle. Why it can work like this? Ans: Because its Internal Structure! EMT2461 Dr. Li 9

10 Internal Structure of DC Servo Motor Disassemble a DC servo motor: Copyright by engineersarage.com EMT2461 Dr. Li 10

11 Internal Structure of DC Servo Motor Insides components of a DC servo motor: Copyright by engineersarage.com EMT2461 Dr. Li 11

12 Internal Structure of DC Servo Motor Map the diagram with real components: Copyright by engineersarage.com EMT2461 Dr. Li 12

13 Position Control of DC Servo Motor We have learned that: Pulse width determines the rotation angle. What the complete control signal should be? Period = 20ms Generally, the pulse period is 20ms! (i.e., the pulse has a fixed Freq. of 50Hz) EMT2461 Dr. Li 13

14 Difference from PWM The pulse signal for controlling a servo motor s position is different from standard PWM signal used to control the speed of a regular DC brushed motor: EMT2461 Dr. Li 14

15 Use Arduino to Control DC Servo Motor How to wire a servo motor with Arduino? Probably you find a wiring schematic online as the following: Can you use this schematic for your servo motor? Or: what you need to check before you use this schematic? EMT2461 Dr. Li 15

16 Use Arduino to Control DC Servo Motor Always check the datasheet: Make sure the voltage is in right range; If you want to directly connect motor to Arduino 5V/3.3V pin: Make sure the current your motor is going to draw is NOT beyond Arduino s capability! Remember: Arduino svcc pin can only provide 200mA! Arduino s I/O pin can only provide 40mA! You are highly suggested to use separate power for the motor! Do NOT blow your Arduino!! EMT2461 Dr. Li 16

17 Datasheet of Servo Motor Datasheet of Hitec HS-322HD servo motor: Operating Voltage: Volts Dimensions: See Schematics Weight: 1.52oz (43g) Stall Torque (4.8V): 42 oz/in (3.0 kg/cm) Stall Torque (6.0V): 51 oz/in (3.7 kg/cm) Current Drain (4.8V): 7.4mA/idle and 160mA no load operating Current Drain (6.0V): 7.7mA/idle and 180mA no load operating Control System: Pulse Width Control 1500usec Neutral Required Pulse: 3-5 Volt Peak to Peak Square Wave Operating Speed (4.8V): 0.19sec/60 at no load Operating Speed (6.0V): 0.15sec/60 at no load Operating Angle: 40 Deg. one side pulse traveling 400usec Direction: Clockwise/Pulse Traveling 1500 to 1900usec EMT2461 Dr. Li 17

18 Use Arduino to Control DC Servo Motor The Sweep example in Arduino IDE: #include <Servo.h> Servo myservo; // create servo object to control a servo // a maximum of eight servo objects can be created int pos = 0; // variable to store the servo position void setup() { myservo.attach(9); // attaches the servo on pin 9 to the servo object } void loop() { for(pos = 0; pos < 180; pos += 1) // goes from 0 degrees to 180 degrees { // in steps of 1 degree myservo.write(pos); // tell servo to go to position in variable 'pos' delay(15); // waits 15ms for the servo to reach the position } for(pos = 180; pos>=1; pos =1) // goes from 180 degrees to 0 degrees { myservo.write(pos); // tell servo to go to position in variable 'pos' delay(15); // waits 15ms for the servo to reach the position } } EMT2461 Dr. Li 18

19 Use Arduino to Control DC Servo Motor Servo.h : a library with Arduino IDE, which provides many functions for user to connect, initiate, and control a servo motor with Arduino. Functions in Servo.h : Servo. attach(port #); //connect a servo motor with port# of Arduino Servo.write(angle); // To control the servo motor to rotate to // position defined by angle degree. EMT2461 Dr. Li 19

20 Today s Lab: Step i): Connect the provided or your own servo motor to Arduino. You are highly suggested to use separate power for the motor. Use CAUTION to directly connect motor to Arduino 5V/3.3V pin! Note: connect grounds together to form a common ground! Step ii): Open the example sketch Sweep and test it on your motor. Use oscilloscope to display the control signal applied on the motor. Step iii): Refer to the example sketch of Sweep and write your own sketch to control the servo motor stops at 30, 90, 120, and150. Pause the motor s rotation for 5sec at each angle. Display the control signal on oscilloscope. Read the pulse width and frequency of each control signal. When you finish the 3 steps, report to the instructor. Function you need to use: Servo. attach(pin#); Servo.write(angle); EMT2461 Dr. Li 20

21 Question? EMT2461 Dr. Li 21