Anatomy of a Quadrotor

March 18, 2012

A quadrotor has a relatively simple mechanism and components, compared to other flying machines, but the can still be quite baffling to the beginner. The aim of this article is to give an overview of the key parts of the machine

Quadrotor Components

The key components of a quadrotor

Propeller

The propeller is used to provide the thrust for the quadrotor and is directly attached to the motor. The size of the propeller is important as it directly affects power consumption and lift. If it is too small the propeller wont supply enough lift. If it is too big, it will drain the battery and put stress on the motors.

Propellers for a Quadrotor

Quadrotor propellers

The propeller/motor unit is arranged so that there are two that turn clockwise and two that turn counter-clockwise. This arrangement neutralises rotation (yaw) so that the quadrotor is stable in the air. Yaw, height, speed and direction are controlled by varying the speed to the four propellers.

Motor

There are essentially two types of motor that can be used on a quadrotor, these are brushed and brushless. A brush is the component used to conduct a current (power) from the stationary wires to the rotating shaft (armature). The electricity is used to create a magnetic field, which causes the shaft to turn, which the propeller is fixed to.

Brushed Motors are cheap and easy to use, but the contact between the brush and the rotating shaft creates friction. This friction reduces the efficiency of the motor by slowing it down and  introduces mechanical wear which reduces the lifetime of the motor.

Brushless Motors generate rotation in a different way, and brushes are not needed. This means that they generate more power, have a greater efficiency, are more reliaable. less noise and a longer lifetime than brushed motors. The main disadvantage with brushless motors is that they are expensive.

Flight Control Board

Quadrotor Flight Control Board

A typical flight control board from www.abusemark.com

The flight control board is a critical element of the quadrotor. Without recent advances in computing, it would not be possible to fly the the quadrotor at all. The flight control board is essentially the brains of the machine . It contains accelerometers, gyroscopes and barometers to monitor how the quadrotor is flying in relation to the instructions given to it. If it is going off course then this unit will change the power being given to the motors to automatically correct for any minor instabilites and keep the qaudrotor flying evenly.

Frame

The frame is what all the other important bits and pieces are attachesd to. There are pre-fabricated frames that you can buy off the shelf, or you can make one yourself. DIY frames require tools, time and some ability to be able to make them, so most beginners should stick to custom frames.

The frame has to be lightweight, strong and rigid. The arms of the frame should be cheap and easy to replace in the event of a crash.9of which there may be a few!)

Carbon composite frames are  used the more expensice quadrotors, but aluminuium ones are common, especially for home build ones as they are cheap and easy to make and replace.

Depending on the use of the quadrotor, you might need to considere a frame where a “payload” can be added, such as a camera.

Batteries

The battery used in the quadrotor is an important element of the aircraft. The weight and power generated are the most critical characteristics.  Bigger batteries are capable of generating more power and lasting longer, but if they are too large the quadrotor may not be able to fly very well, if at all. Lithium polymer batteries are the most powerful batteries available.

Receiver

This is the part of the quadrotor that recieves the ignals from the controller (transmitter). There is a wide range of receiver and transmitter combination and the AR Parrot uses wi-fi technology to controll the quadrotor from smartphones and iPads. However, most use traditional remote controls and radio frequency technology.

Landing Gear

Each type of quad will have a different landing gear, however there is only a real choice to be made when you are building your own. Many people use bits and pieces that are lying around the house. One thing that has to be considered though is the contribution that the landing gear will make to the overall weight. It should be as light as possible.

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