Chapter 2: Your Boe-Bot's Servo Motors

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Chapter 2 Your Boe-Bot's Servo Motors
Presentation based on"Robotics with the
Boe-Bot" By Andy LindsayParallax, Inc
Presentation developed byMartin A.
HebelSouthern Illinois University
Carbondale College of Applied Sciences and
Arts Electronic Systems Technologies 7/6/04
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Continuous Rotation Servo

• Used to provide drive motion for the
  Bot.
• Standard Servo Used for positioning, such as
  with RC airplane rudder and flaps.
• Continuous Rotation Servo Rotate in a certain
  direction and speed.

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Tracking Time

• PAUSE is used to have the BASIC Stamp wait a
  short amount of time.PAUSE duration
• Duration is in milliseconds (mS) or 1/1000th of a
  second, 1-65535PAUSE 1000

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Repeating Actions

• A DO.LOOP is used to repeat a sequence of
  commands.DO 'Commands to performLOOP

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Basic Electronics

• Voltage (V or E) Potential difference between 2
  points. Volts.
• () - A lack of electrons
• (-) A surplus of electrons
• When a circuit is formed, electrons will flow to
  equalize out the 2 sides.
• Current (I) The measure of the flow of
  electrons. Amps.
• Resistance (R) Opposition to current flow. Ohms.
• Ohm's Law I V/R

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Resistors

• Devices used to insert resistance, or oppose
  current flow. Used to limit current flow.
• Color codes are used to indicate the value.

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• From Appendix C

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The LED

• LED Light Emitting Diode
• Diode Device which allows current to flow in
  only one direction.
• To operate it must be installed correctly with
  respect to polarity.

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• A regular LED can be damaged if current exceed
  20mA (milliamps) or 0.02 amps.
• Apply ohm's law to find the resistor size that
  will limit current to 20mAwith a 5V supply.I
  V/R

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LED Circuit Schematic
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The BreadBoard

• Breadboards are used to make connections between
  devices.

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Building the Circuit
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Pictorial or Wiring Diagram
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Code to Blink LEDs
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Task

• Perform Chapter 2 up to this point (page 52),
  including "Your Turn- Blink the other LED"

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Additional The Speaker/Buzzer

• A small piezoelectric speaker is included with
  your kits.
• A frequency can be made on it using the FREQOUT
  command.FREQOUT pin, duration, frequency
• pin Pin it is connected to.
• duration Length of time in milliseconds.
• frequency Frequency to play, measured in Hertz
  (Hz).

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• Sound the Speaker for 1 second at 1000Hz

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Pseudo-Code

• Pseudo-Code is English-like statements that
  describes the steps the code will perform
• From the pseudo-code, the program code can be
  developed to match the actions needed.

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Group Task

• Write a program that will
• Display in DEBUG Window "Stop! Police!"
• Turn ON P12 LED
• Sound a tone for ½ second at 1000Hz
• Turn OFF P12 LED
• Turn on P13 LED
• Sound a tone for ½ second at 2000Hz
• Turn off P13 LED
• Repeat sequence

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Individual Task

• Develop a program to perform the following
• Turn on P12 LED
• Wait ½ second
• Turn on P13 LED
• Wait ½ second
• Sound tone at 3000 Hz for 1 second
• Turn off P13 LED
• Wait ½ second
• Turn off P12 LED
• Wait ½ second
• Sound tone at 2000 Hz for 1 second
• Repeat entire sequence

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Servo Signals

• Servos are controlled with a high pulse lasting a
  short time, and repeated.
• The PULSOUT instruction can be used to send a
  short pulse.PULSOUT Pin, Duration
• Pin Pin device is connected to.
• Duration Time in 2?S (microsecond) intervals,
  1-65535. Microsecond 1 millionth of a
  second.PULSOUT 12, 1PULSOUT 13, 2

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Servo Signals

• Typical servos require a pulse of 1mS to 2mS to
  define the direction/position.
• A 20mS pause must be between each pulse.
• What values of PULSOUT are in the valid range?

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Connecting the Servos
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Centering the Servos

• The pulse width defines the direction and speed
  of the servo motor.
• 1000 Maximum speed one direction
• 750 Stopped
• 500 Maximum speed other direction
• Use the servo center programs to ensure it is
  stopped at 750.

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Task

• Perform Activities 3 and 4

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Storing and Counting Values

• Variable are used to store values
• Variables much be declared prior to being used.
  Declaring a variable is giving it a name, and a
  size to hold.VariableName var Size

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• DEBUG ? is short hand to display the value of a
  variable or pin.

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Counting and Controlling Repetitions

• FORNEXT loops can be used to control the number
  of repetitions a segment of code takes.FOR
  StartValue TO EndValue STEP StepValueNEXT

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What will this code do?

• Freq VAR Word
• DO
• FOR Freq 1000 to 5000 Step 100 DEBUG ?
  Freq
• FREQOUT 4, 100, Freq TOGGLE 12 TOGGLE
  13NEXT
• LOOP

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Testing Servos

• To control the servo, send a series of pulses
  with values between 500 to 1000 (1-2mS)
• Changing the value will change the direction and
  speed to some extent.

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FORNEXT to Control Servo Run Time

• The FORNEXT Loop can be used to control how long
  to drive a servo.

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TASKS

• Perform Activities 5 and 6
• Test servo speeds and directions on pages 79 and
  80.

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Group Task

• Put LEDs on P7, P8, Speaker on P4
• Write a program to perform the following
  pseudo-code.
• Turn on P7 LED
• Wait one second
• Rotate P12 servo CW for 1 second
• Repeat 3 time
• Sound 2000Hz tone for 2 second
• Pause 1 second
• Turn on P8 LED
• Rotate P13 BOTH servos CCW
• End the program

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Review
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