Quadrotor: An eye in the sky [November 2012]

Developed by Mumbai-based Robosoft Systems, micro air vehicle Quadrotor is gradually evolving as an eye in the sky
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 manoeuvrability and hovering ability.
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 (Figure 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. According to Fahad Azad, Managing Partner of Robosoft Systems, “A four-rotor design allows quadrotors to be relatively simple in design yet highly reliable and manoeuvrable. Cutting-edge research is continuing to increase the viability of quadrotors by making advances in multi-craft communication, environment exploration, and manoeuvrability. 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.”
Mumbai-based Robosoft Systems is primarily a research and development based company in the field of embedded system design, VLSI and robotics since 2008. Robosoft designs and manufactures microcontroller development tools and small single-board computers that are used by electronic engineers, educational institutions, and hobbyists.
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. To power and control the rotors, a battery and microcontroller are placed near the centre 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,” expressed Mr. Fahad.
Figure 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. Because of these small dimensions, quadrotors are better suited for indoor and outdoor urban environments than most other air vehicles,” he adds. 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.
When the quadrotor begins to tip to one side, a microcontroller receives a signal from the IMU and calculates new motor commands that will compensate for the tipping motion. These motor commands are then sent to the motor controllers, which adjust the speed of their respective rotor to the proper degree. At this point, a corrective force returns the quadrotor to a level position. In practice, this whole process needs to happen at least 100 times per second to keep the quadrotor in the air. Motors and electronics that could update at this rate were not readily available until a few years ago.
Application“One of the best applications for the Quadcopter is to obtaining high quality aerial pictures for making movies or an instrument for being eye in the sky during day or night time. Due to its small size and micro takeoff space the applications will evolve as time comes,” Mr. Fahad explained.

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