Page 31 - The Definitive Guide to Building Java Robots

Preston_5564C01.fm Page 12 Friday, September 16, 2005 6:36 AM

12 CHAPTER 1 ■ A PRIMER

Organizing Your Components

The first thing I did was model the physical connections between my PC and my robot. I found
that having three layers simplified the grouping. You can choose another arrangement for your
robot, but this is what worked for me. An outline of the layering is shown in Table 1-4.

Table 1-4. Layers in Robotics Programming
PC Layer Control Layer Device Layer
This is the layer you are most This layer represents the third-party This is the layer that represents
familiar with. It will contain your controllers. These controllers allow the hardware devices you’ve
interfaces to your peripherals like you to communicate in both the connected.
your serial port, parallel port, language of a robot and the language
webcam, sound output or input of a computer.
devices, etc.
Serial Port Parallax Stamp Robot Arm
Webcam MiniSSC-II Servo Controller Sonar
Sound Card Microcontroller Compass
Database Differential Drive
Logic Robot Leg

Modeling Your Hardware and Behavior

Once you organize the components you have to work with, it’s time to create some “soft”
models of those hardware components.

• Pick a name (for example, PanTiltCamera).
• Model what you want it to do (move up/down, move left/right, take a picture, and so on).
• Stub out your class.

• Plan what can go wrong and how you want to deal with it.
After you’ve modeled your hardware and behavior, you should be ready to calculate the
synchronization between the two.

Timing
Timing in life is important; timing in robotics is mandatory. If you have a larger microcontroller,
I would suggest using flow control (for example, having your PC and microcontroller negotiate
when each are ready to talk). But since I only have 16 I/O ports with my BASIC Stamp 2, I’ll
manually synchronize the serial communication. You should be aware of how long things take
though.
For example, a 9600-baud communication rate with your microcontroller takes about 3 feet
per character. If you have three characters to transmit, like the bearing of your compass, it
could take less time to execute the command than it would to get the data back from your serial
connection.