Intro to Engineering II for ECE: Lab 3 Controlling Servo Motors Erin Webster and Dr. Jay Weitzen, c 2012 All rights reserved

Transcription

1 Lab 3: Controlling Servo Motors Laboratory Objectives: 1) To program the basic stamp to control the motion of a servo 2) To observe the control waveforms as the motion of the servo changes 3) To learn about the use of capacitors as a filtering device. Before You Come To Lab: Download and read chapter 4 in the WAM book. Caution Please Pay Attention to this Warning! DANGER Electrolytic Capacitors can explode if connected reverse polarity. Take Care when connecting and applying power. Wear Safety Glasses!

2 Section 1: Servo Rotation Intro to Engineering II for ECE: Lab 3 Controlling Servo Motors Build Circuit 4 12 shown below, and on p.112 in the textbook: Connect ADI pin 1+ here and 1 to ground The servo is controlled by bursts of signals spaced 20mS apart. A high signal can last between 1mS to 2mS. Changing the width of a pulse to control a servo is known as Pulse Width Modulation or PWM. The PULSOUT instruction is used to send the signals: PULSOUT pin, duration pin: Defines which I/O pin to use. duration: defines how long the pulse should last in 2 microsecond (us) increments. 1 S = seconds. 1 ms = 1000S For a command of: PULSOUT 14,750 This would be sending a pulse that lasts 750 x 2 S = 1500 S or 1.5mS on pin 14. Changing the width of a pulse to control a servo is known as Pulse Width Modulation or PWM.

3 Program the Basic Stamp, reference p. 115: Enter and Run Servo Test.bs2 shown below: ADI Discovery Module: Using Scope 1, record the signal at each position (Note: Adjust the scope s time division (you should be seeing square waves), if the time division is too coarse a square wave will appear distorted). Record each of the three sections of the code: First Section "Counter Clockwise 10 o'clock"

4 Second Section "Clockwise 2 o'clock" Third Section " Center 12 o'clock"

5 Section 2: Servo Velocities Program the Basic Stamp, reference p : Using the circuit from Section 1: enter and run ServoVelocities.bs2 Describe how incrementing an decrementing the counter effected the servo:

6 Section 3: Use Push Buttons to control speed and direction of the servo Add the Circuit 4 20 shown below, and on p.129 in the textbook: Program the Basic Stamp, reference p : Enter and Run ServoControlWithPushButtons.bs2

7 ADI Discovery Module: Observe the signal on pin 14 and record it below: Describe how this program works:

8 Section 4: Open Ended Design Project: Modify ServoControlWithDebug.bs2 so that it monitors a kill switch: If the Kill switch (P3 pushbutton) is pressed, the program should enter the Stop state. If the Start switch (P4 pushbutton) is pressed, the program should enter the Start state. In the Stop state, the Debug Terminal should not accept any commands. It should display: Press Start switch to start servo. In the Start state, the program should function normally. If power is disconnected and reconnected, the program should enter the Stop State. Hint: Think about adding a variable to keep track of your start and stop states. Hint: Use debug to see what your variables are seeing, and the ADI scope to see your voltages. Example Program: ServoControlWithDebug.bs2, reference p. 122: NOTE: You are MODIFYING this code, do NOT submit it as is!

9 List your code here: Intro to Engineering II for ECE: Lab 3 Controlling Servo Motors