Basics of Operation
Why are the new vehicles so different from toy helicopters and planes? In a nutshell, it comes down to vast improvements in batteries, motors and in flight control hardware and software. The new breed of LiPo batteries (lithium polymer) have a higher power to weight ratio, meaning they can power heavier devices and keep them in the air longer. The same batteries also power the electronics and cameras your quadcopter will use.
The current crop of batteries are capable of keeping quadcopters aloft for periods from 5 to 25 minutes, quite an accomplishment when you consider some of these machines can travel miles in that time. More advances are assured in the future, so specifications will continue to improve.
A quadcopter uses four propellers, two of them rotating clockwise and two counterclockwise. This creates a balanced effect, so that the quadcopter can hover with reasonable stability. The following diagrams and descriptions will help the newbie understand how the brains and brawn of these machines work in tandem to provide the magic of unmanned flight.
Aerodynamics of Quadcopters
Truth is they have no real aerodynamics! These are basically motors and propellers that can only fly with the help of their computer brains. Unlike a plane or even a regular helicopter, failure of an engine or part will invoke gravity without any glide ratio at all. Hobbyists have therefore been able to build quadcopters out of tupperware boxes (for landing in water), foam boards ($5 in frame costs), plastic wheels and other such materials.
It does help for quadcopters to be streamlined as wind will not have as much of an effect on them.
Like a Human (or robot)
It may help to consider the quadcopter as a robot, with the basic internal functions attempting to mimic those of your own body. The first steps in movement are your eyes, ears and other senses gathering input or instructions from the environment around you. With a quadcopter, this would be the instructions being given to the drone by the pilot or by a set of pre-programmed steps “listening” to many sensors in the drones flight control system (onboard computers). In most cases the operator will be actively giving instructions to the flying quadcopter through the use of a radio control transmitter or a smartphone/tablet. You will notice that many discussions of quadcopters use the term “R/C” in them – which means “Radio Controlled”.
Item #1 below is the transmitter (TX – sometimes called a Remote), usually handheld, which is beaming the instructions to the drone. The part labeled #2 is the receiver – this is also a radio part and its function is to talk to your transmitter and hand over the instructions to item #3, the Flight Controller, which sends power to #4, the motors.
The flight controller (F/C) is the CPU (central processing unit) or brain of the quadcopter. Like a human brain, it has pathways for information both in and out. Here are the main inputs:
1. Power from the batteries
2. Instructions from your transmitter (usually in your hands).
3. Status reports from a number of tiny instruments (sensors) built into the quadcopter main circuit board. These may include gyroscopes for leveling, accelerometers to measure speed and direction, barometers and sonar for height control and GPS and compasses for determining your position on the earth. Simple quadcopters may only have gyroscopes, while very advanced models will have many or all of the above. Some recently released camera drones have added “Computer Vision” – the ability for the drone to see and recognize (and avoid or follow) objects!
Based on the combination of all these inputs, the Flight Controller (FC) makes decisions, most importantly exactly how much electrical power to apply to each of the four motors (#4 in the picture).
As an example, if you desire to fly forward, that requires the quadcopter to tilt in that direction – you should be familiar with this type of flight by having watched helicopters. By tiling forward, the propellers act to keep the vehicle in the air and to propel it forward simultaneously. In the case of a quadcopter, the command to move forward will put less power to the front two motors and more to the rear two, resulting in the machine leaning forward and being propelled in that direction. Side to side movement is accomplished in much the same way – the FC “brain” eases up on two propellers and powers the opposite two slightly stronger.
The comparison with your body is that the flight controller is the brain, the wires are the blood vessels and nerves, and the motors are your muscles, limbs and hands. Like your body, each system constantly gives feedback to the brain, resulting in amazing capabilities of movement.