This article is the first of three in a series discussing GPS navigation for ground-based robots. The concepts are relatively complex but are simplified to make things easier to understand.
In the 80s when I first starting building robots I found there were roughly three ways I could program my robot for autonomous navigation depending on the sensors equipped. The first option was basic roaming where the robot would simply move in a given direction until a sensor detected something in the path at which point the robot would choose a new path based on where the object was detected. The second option was to use beacons or a line to guide the robot from one point to another.
Finally a third method known as dead reckoning was demonstrated to me via a plastic toy tank created by Milton Bradley in 1979 (See Figure 1). This six-wheeled toy tank, known as “Big Trak” was probably the most advanced toy I had seen in awhile. It used an internal optical wheel encoder to determine how far it moved and could execute commands telling it how far to go in a direction, how much to turn and even to stop for periods of time.
Wide Open Spaces
In a living room or kitchen environment the Big Trak could be placed in a fixed spot at a fixed angle and expect to navigate using dead reckoning with fairly good repeatability. However the playing field opens up for vehicles that can move faster and farther such as radio controlled boats, planes and even larger robots. In these situations dead reckoning really isn’t that useful. To complicate things even more, most typical sensors don’t have the range to handle avoidance at the distance and speeds these vehicles move at. Lines become useless and beacons become impractical. In a larger arena you really need something that works on a much larger scale.
What wasn’t available to the general public 20+ years ago has now become widely available and extremely accessible to the robotics hobbyist. GPS, or Global Positioning System can provide larger vehicles and robots a new method of navigation. GPS receivers are integrated into cell-phones, vehicles and even camcorders now. For the hobbyist GPS has become widely available from sources such as Parallax for well under $100.00 (See Figure 2). Using GPS, a robot, boat or plane could easily travel great distances autonomously with very little extra hardware.