Editorial Feature

Intermediate Robotics - Navigation: Compass

A compass is a navigational device capable of showing directions of reference which is relative to the earth’s surface. It can be a valuable sensor used in robots for navigating its surroundings.

The most common type of compass is a simple magnetic compass that utilizes the magnetic pull of the Earth's North Pole to determine which direction is north.

A fluxgate compass, on the other hand, is a more sophisticated, electronic version of the magnetic compass that requires electricity to operate.

Magnetic Compass

A magnetic compass is aligned with respect to the earth’s magnetic field. This compass consists of a magnetized pointer that is usually marked at the North end, and a magnetized bar or needle turning freely upon a pivot.

The magnetic field exerts a torque on the needle which moves the needle so that one end of this component is pulled toward the Earth’s North magnetic pole, and the other toward the South magnetic pole.

Modern-day technology still maintains the way this instruments works. Professional compasses usually have bar magnets glued to the underside of a disk pivoted in the center.

Digital Compass

A digital compass provides the measurements based on the Earth's magnetic field for the navigation of a robot.

This digitalised version of a standard compass consists of tiny MEMS nano-structures that tend to bend due to electromagnetic fields.

When these MEMS structures are subjected to any form of electromagnetic field, these structures bend by an amount that can be electrically detected.

The digital compass output data can be provided in the form of a digital or a pulse width modulated signal.

Applications

The major applications of a navigation compass in the robotic system include:

  • Motion control
  • Detection of the heading of mobile robots.

Autonomous navigation involving localization, obstacle avoidance and road following is demonstrated by the REKNODrive UGV autopilot system by Rekno, a technology company involved in the development of mobile robotics.

The localization module exploits data fusion of GPS and a compass. This module helps the autonomous system to detect a wide range of obstacles encountered in an outdoor environment. The compass integrated into this system is part of the fundamental principles of how this robot navigates.

Rekno autopilot system for outdoor navigation. Video courtesy of Rekno Robotics

Products on Market

Given below are some of the navigation compass products that are commercially available on the market.

Compass Module 3-Axis HMC5883L

The Compass Module 3-Axis HMC5883L designed by Parallax is a low-field magnetic sensing device with a digital interface. This module is ideal for small projects such as UAVs and robot navigation systems.

The main functional purpose of this compass involves converting any magnetic field to a differential voltage output on 3 axes. It can also be used with a wide range of microcontrollers with different voltage requirements.

The key features of the Compass Module 3-Axis HMC5883L includes:

  • Precision in-axis sensitivity and linearity
  • Wide magnetic field range
  • Fast 160 Hz maximum output rate.

Devantech CMPS03 Magnetic Compass Module

Designed by RobotShop, the Devantech Magnetic Compass Module CMPS03 allows a user to identify the orientation of robot in relation to the North direction according to the calibration.

The key features of Devantech Magnetic Compass Module CMPS03 include:

  • Outputs heading via PWM or I2C
  • Magnetic compass with 0.1 degree of resolution and 3 to 4 degrees of accuracy
  • Requires only 5 V.

Sources and Further Reading

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