Specifications

The Enhancement of a Multi-Terrain Mechatron for Autonomous Outdoor Applications

4.4 ELECTRONIC COMPASS

An electronic compass provides robot heading information for the navigation and

guidance system. Robot positioning by odometry alone rapidly accumulates errors

particularly in tracked vehicles due the slippage of the drive components. The

addition of a heading sensor to the control system can correct direction errors and

increase the accuracy of the robot positioning software.

Figure 4.8 Earth's magnetic field

The Earth's magnetic field is approximately 0.6 gauss in an open-air environment

with the field lines directed from the magnetic South Pole to the magnetic North Pole.

The magnetic field vector is horizontal near the equator but becomes increasingly

vertical near the poles (inclination or dip angle), as shown by Figure 4.8. The field

lines form the basis for magnetic compassing as units can be designed to measure the

field strength in the plane (2-axis sensors) thus providing a measure of heading.

4.4.1 Previous Module

The electronic compass originally selected for this project (Cordes, 2002) was chosen

for its significantly lower price than most other units available at the time and as a

result functionality was limited. The Vector V2X, manufactured by PNI Corporation

is a 2-axis magnetometer that measures magnetic field in a single plane. Accuracy

when level is ±2° RMS however, this decreases rapidly when the unit is tilted.

http://www.magneticsensors.com/landnav.html