Computer Science 014 LEGO Robot Engineering Williams College Winter 2007

Agenda

• Announcements
  • This week only: a Friday meeting
  • When leaving the lab, please clean up your station
    • unplug the adapter from the Mac
    • put the adapter away in the cabinet (second shelf down)
    • put your tools and wires in the tool box, and store it in the cabinet
    • log out of the Mac
    • plug in your Handy Board to keep the batteries charged
    • clean up the work area (wires, etc)
• The Handy Board
  • You saw last time some of what the Handy Board can do
  • The Handy Board is based on the Motorola 68HC11 microprocessor
    • a very popular (not to mention old) processor, running at 2 MHz (yes, MHz)
    • 32 KB (yes, KB) of memory
    • not much, but we'll be able to write reasonably complex programs
  • Motors: the Handy Board has 4 motor ports (0, 1, 2, 3)
    • Motors may be set a "forward" or "backward" direction
    • Power level of motors may be controlled, ranging from 100, full power in the "forward" direction to -100, full power in the "backward" direction
    • Really only seven degrees of power, but these numbers are used; still a fair bit of control
    • Interactive C commands:

      fd(0);		turns motor 0 on in the forward direction at full power
      fd(1);		turns motor 1 on in the forward direction at full power
      fd(2);		turns motor 2 on in the forward direction at full power
      fd(3);		turns motor 3 on in the forward direction at full power
      bk(0);		turns motor 0 on in the backward direction at full power
      bk(1);		turns motor 1 on in the backward direction at full power
      bk(2);		turns motor 2 on in the backward direction at full power
      bk(3);		turns motor 3 on in the backward direction at full power

      To control motor speed:

      motor(0, 50);		turns motor 0 on in the forward direction with a power level of 50%
      motor(3, -10);		turns motor 3 on in the backward direction with a power level of 10%
      motor(m, s);		where m is the name of the motor and s is the power

      Note that:
      • "Power" is not the same as "Speed", especially in a well-geared motor
      • motor(m, s) can be used either to turn the motor on at a specific level of power or can be used to change the level of power once the motor is running
      To shut a motor off:

      off(0);		shuts off motor 0
      off(1);		shuts off motor 1
      off(2);		shuts off motor 2
      off(3);		shuts off motor 3
      alloff(); or ao();		shuts off all motors

      Note the use of semicolons above - each statement (i.e., command) in C must be terminated by a semicolon.
  • Sensors: the Handy Board has 16 sensor ports (0-15)
    • Ports 0-6 for analog (continuously varying) sensors, e.g., our light sensors
    • Ports 7-15 for digital (on/off) sensors, e.g., our touch sensors
    • digital(11) gives the value of the digital sensor connected to port 11. So if a touch sensor is connected to that port:
      • 1 = true = touch sensor pressed
      • 0 = false = touch sensor not pressed
    • analog(0) gives the value of sensor port 0. It returns a value between 0 and 255. For example, if a photocell is attached to port 0, might return
      • 0 = most bright
      • 255 = totally dark
      Note that the actual values will likely be different, but lower numbers will always mean "lighter" and higher numbers will always mean "darker"
      Note that there are no semicolons here.
      If these are used in isolated cases (i.e., not as part of a larger program), then we will use semicolons. When used in a program, however, these will typically not appear alone. They will appear in the context of other code. In those cases, they will not be immediately followed by semicolons.
    • A note about Cadmium Sulfide photocells: Photocells are resistors. The resistance varies in proportion to the amount of light striking the surface of the device. The greater the intensity of the light, the lower the resistance.
    • We can also sense the state of the start and stop buttons: start_button() gives the state of the start button on the Handyboard
      • 1 = true = the start button is pressed
      • 0 = false = the start button is not pressed
      stop_button() gives the state of the stop button on the Handyboard
      • 1 = true = the stop button is pressed
      • 0 = false = the stop button is not pressed
• A few simple Interactive C programs
• The Robot Base
  • For the first part of the course, you will be building a robot similar to the "HandyBug" described by Martin. There is a copy of the relevant chapter for each group to use for reference.
  • My robot is pretty much the HandyBug. You can take a look at it as you design yours.
  • You are free to build your robot with any design, so long as it uses two motors to drive wheels, can accomodate two front-side touch sensors and two light sensors, and (later) a sonar.
  • Make sure your robot is sturdy - it will bump into things.
  • Make sure you mount the Handy Board securely and in a way that makes it convenient to plug it in, wire up sensors and motors, and so you can reach the start and stop buttons easily!
  • Pictures of some previous designs:
    • Fall 1999 CS 108
    • (others not online)
  • You should also read Martin's article The Art of LEGO Design to get some ideas.
• Interactive C program to test the robot base

Examples

• beepthreetimes.c
• beep.c
• baseTest.c