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Written by: Josh Villbrandt
Written on: July 1st, 2010
Tags: aerospace engineering, security & defense
Thumbnail by: Draganfly Innovations, Inc.
About the Author
Josh was a junior studying Aerospace Engineering. In his free time, Josh enjoys programming for the Aerial Robotics Team, working in the shop for the AeroDesign Team, and tossing around Frisbee with friends. Upon graduation, Josh hopes to work in the Aerospace industry, possibly with a focus in robotics and UAVs.
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Volume XII Issue II > The Quadrotor’s Coming of Age
The quadrotor is an emerging Micro Air Vehicle (MAV) that may have limitless applications. Departing from a century old design, modern quadrotors are evolving into small and agile vehicles. After already proving their usefulness as aerial imaging tools, new research is allowing quadrotors to communicate intelligently with other autonomous vehicles, to explore unknown environments, and to maneuver in dense surroundings with speed and precision. Individually, these advances will allow quadrotors to complete missions such as long-term surveillance and search and rescue. However, if all of these developing technologies are combined, quadrotors will be capable of advanced autonomous missions that are currently not possible with any other vehicle.

Introduction

In the last few decades, fixed-wing Unmanned Aerial Vehicles (UAVs) have become more popular and more commonly used for a variety of applications. Militaries around the world use UAVs for routine surveillance and to carry out basic attack strategies. Civilian applications include tasks from border protection to search and rescue. However advanced fixed-wing UAV technology is becoming, there remains the need for craft with greater maneuverability and hovering ability.
Gabe Hoffmann/Stanford University
Figure 1: The STARMAC of Stanford University is a typical modern quadrotor design.
Helicopters have been able to fill the niche of full-sized, manned vehicles. Now, a new type of Micro Air Vehicle (MAV) is emerging as the small-scale equivalent of the full-sized helicopter. This new craft (see Fig. 1) is commonly referred to as a quadrotor. While the quadrotor is also rotor-based, it has a few key differences that set it apart from traditional helicopters and make it particularly attractive as an MAV. A four-rotor design allows quadrotors to be relatively simple in design yet highly reliable and maneuverable. Cutting-edge research is continuing to increase the viability of quadrotors by making advances in multi-craft communication, environment exploration, and maneuverability. If all of these developing qualities can be combined together, quadrotors would be capable of advanced autonomous missions that are currently not possible with any other vehicle.

What is a Quadrotor?

In general, a quadrotor is a type of rotorcraft that uses two pairs of counter-rotating, fix-pitched blades for lift. The use of fixed-pitched blades allows quadrotor propellers to often be connected directly to four individual motors without the need for complicated linkages that control pitch. These motors are then connected in an ‘X’ configuration. To power and control the rotors, a battery and microcontroller are placed near the center of the craft. Changes to the altitude and attitude (the height and orientation with respect to the ground) of the craft are achieved by varying the speed of individual rotors. Fig. 2 shows the typical layout of these components and identifies the different rotor changes needed to adjust the state of the craft. With such a straightforward design, it is easy to build vehicles that are much smaller than traditional rotorcrafts. Many of the quadrotors currently in development have a total system weight of about 1.5 kg and a rotor tip to rotor tip length of 0.5 m. Because of these small dimensions, quadrotors are better suited for indoor and outdoor urban environments than most other air vehicles.
Bouabdallah, Murrieri, Siegwart/IEEE Conference on Robotics and Automation, 2004
Figure 2: Typical layout of quadrotor components and rotor speed variations for craft attitude and altitude adjustment.
Such a machine has a few additional benefits over traditional helicopters. With a traditional helicopter design, a large primary rotor is used to generate lift, and changes in thrust are generally achieved by varying the pitch of the rotor blades because changing the speed of one large rotor requires too much time. Furthermore, the mechanical parts needed to adjust the pitch of the fast-spinning blade are complex and difficult to maintain. Quadrotors, however, can achieve thrust changes by varying the speed of each of the smaller and lighter rotors, allowing the complicated variable pitch components to be avoided. In addition, because of the single primary rotor, a traditional helicopter must have a tail rotor to counteract the torque created by the primary rotor. Quadrotors, on the other hand, do not need a tail rotor, since the counter-rotating rotors cancel out each other’s torques. These differences reduce quadrotors to a vastly simpler design that is cheaper to build and easier to maintain.