What is a RC Quadcopter?

A RC quadcopter is an aircraft that falls into the category of multi-rotor (or rotor-craft that has more than two blades) and is very similar to a RC helicopter. The main difference (and its most noticeable feature) is that the quadcopter has, as the name suggests, four rotors. The helicopter traditionally has a single main rotor, with an anti-torque tail rotor (the quadcopter does not have a tail rotor).

RC Quadcopter

Quadcopter + Bear (Photo credit: John Biehler)

It seems that the RC quadcopter is now becoming more popular than its helicopter counterpart and there are several reasons for this. Firstly, the quadcopter usually has fewer moving parts and has a much less complex operation than the helicopter. Another thing is that the quadcopter is generally easier to fly than a helicopter: The helicopter often struggles in high wind and is tricky to land where, in contrast, the quadcopter is somewhat insensitive to wind and lands with relative ease. The quadcopter is also very stable due to the four rotors and a sensitive, modern electronics system which gives greater control of the quadcopter. Another important factor is that quadcopters are simpler to build and they are easier (and cheaper) to repair.


RC quadcopter ESC

quadcopter 2013 (Photo credit: eok.gnah)

The RC Quadcopter consists of three main mechanical components which are the frame (the integral core which joins the other parts of the quadcopter together), four motors and propellers (one on each motor). As well as mechanical there are also electrical components and these are the Electronic Speed Control (ESC), controller board, battery and of course, the remote control. An interesting twist in some of the newer quadcopters is that they are controlled via a smart-phone or a tablet.

RC Quadcopter Features and Uses

RC Quadcopter Camera

keycam with gopro compatible mount on quadcopter (Photo credit: eok.gnah)

Modern technology ensures that additional features and functions are constantly being added to quadcopters, such as a mount for a GoPro camera and integrated GPS systems.

The RC quadcopter is able to fly in all directions, can hover and take off vertically. Two of the quadcopter’s rotors move in an anti-clockwise position, while the other two move clockwise. All four rotors are set to spin at different speeds and this allows the aircraft to complete all kinds of movements (rolling, tilting, turning and hovering). Control over the quadcopter’s motion is attained by changing and altering the pitch and rotation or one (or more) of the rotors.

As we have already ascertained, these are exciting times for RC quadcopters, so it stands to reason that they are becoming increasingly popular with the hobbyist community. However, the increased interest and use of quadcopters is not limited to enthusiasts: Unmanned Aerial Vehicles (also known as UAVs) are aircraft that do not have a human pilot on board, such as the quadcopter. These are regulaly used for research, surveillance and military work. They are presently conducting extensive research into possibly being able to use quadcopters (that are capable of autonomous flight) to  substitute humans in dangerous scenarios. For example, being used in the emergency services such as the police or fire-brigade, perhaps even preventing the loss of human life.

How a Quadracopter Works

A quadracopter is a flying machine that operates using four propellers (or rotors). Although designs can vary, there are certain fundamental mechanical and electrical components required. Firstly, the main mechanical components are:

Quadracopter Components

Frame: this is the integral part of the quadracopter as it joins the other components. The frame can come in many designs and sizes yet its main purpose is to ensure that the vibrations coming from the motors are kept at a minimum. Therefore, it is imperative that the frame is made with a strong and rigid material, such as carbon fibre.

Motors: every quadracopterhas four electric motors and these drive the propellers. The motors on a quadracopterare usually out-runners (meaning that the motor is on the outside as opposed to being on the inside).

Propellers: there are four in total, one on each motor. Having four propellers increases the quadracopter’s stability.

Along with the mechanical components a quadracopter also needs various electrical components:

Electronic Speed Control (ESC): this interprets the control information from the controller board and varies the speed and direction in which the quadracopteris moving.

Battery: this powers the quadracopter.

Remote Control: this gives control over the quadracopterfrom the ground, when in flight. quadracopter can now also be controlled via smart-phones or tablets.

Controller board: this is the flight control board. It’s purpose is to ensure stability in flight and does this by passing the information on to the Electronic Speed Control. Controller boards can also be customised to add different functions.

Quadracopter Mechanics

As mentioned, quadracopter use four rotors, with two propellers moving in a different direction to the other two: rotors one and three rotate clockwise while rotors two and four rotate anti-clockwise (the quadracopter would continually spin around if all the propellers moved in the same direction). All four of the propellers work together, at the same time, to create an upward thrust. Varying the thrusts on each one of the propellers controls movement, and this particular design (using four rotors) offers overall increased stability. The weight of the quadracopter is split between the four rotors and therefore, altering the lift and torque of each rotor will control the flight.

Quadracopter Mechanism

A quadracopter has four controllable degrees of freedom and these are: yaw (turns left or right), roll (rolls left or right), pitch (tilts left or right) and altitude. The motion along any of the degrees of freedom is controlled by varying or adjusting the thrusts on each rotor. For example, if you want the quadracopter to roll or pitch, you increase one rotor’s thrust while at the same time decreasing the opposite rotor’s thrust. This must be done simultaneously and at an identical level. This will result in the quadracopter tilting. As a quadracopter tilts, the force vector splits into two components, horizontal and vertical, which will cause two things to occur. The first is that the quadracopter will start to travel opposite the horizontal component and secondly, because the force vector has been split, the vertical component will be smaller. This would cause the quadracopter to fall. To prevent this from happening, increasing the thrust on all four rotors is necessary.

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