Servo - April 2010

By Chris Savage

GPS

Navigation Part 2

38 SERVO 04.2010

In this article, I have built a small robot to test and prove the theories discussed in Part 1 from last month. Something we couldn’t account for previously were the specifics of the robot since it hadn’t been built yet. We also wanted to be able to use this concept and even the code elements on just about any platform.

The first thing to do in this case is to define several key elements of the design before we begin. How large is the robot going to be? How fast will it move? What type of terrain will it traverse? How will it steer?

For our purposes here, my answers were: about the size of a shoe box; no faster than three feet per second; asphalt and/or concrete; and skid steering. An old Lexan chassis I had lying around was perfect for this task (see Figure 1). My robot has four spur gear motors and a two-level platform for mounting the microcontroller and sensors.

Additional Components

I opted to use a Parallax BASIC Stamp 2p module for this system because it is more than capable of reading the raw NMEA data from the GPS receiver, parsing the data, reading the compass, and calculating headings from that data. It can then control the drive system to steer the robot where it needs to go, plus it simplifies the code design for those using a different platform for their robot and controller. The BS2p will mount on a Super Carrier Board which will provide connections to the remaining hardware. The chosen compass module for this application is the HM55B due to its easy integration and existing compatible source code. A serial LCD display, some PING))) sensors, and a heat array sensor (Devantech TPA81) have been installed on this robot. However, for this example, they will not be used and are optional for this part of the project. (These items will be used in Part 3. Be sure to check the Parallax website for the various components listed in this article.)