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This page will cover flying toys as well as larger and more serious drones.

Summary

In recent years the availability of lithium batteries with a high power to weight ratio and of cheap control electronics and sensors has made possible both flying toys of various sorts and drones for professional and serious amateur use. Particularly with toys, damaging crashes are common, but other faults may also arise.

Safety

Be sure you know how to fly your device safely. Rotating propeller blades can be very dangerous.

There are strict laws in many territories governing the use of drones and quadcopters, as well as radio controlled model aircraft of all types. See Legal below.

Basic Principles

The idea of a machine which screws itself into the air dates back to Leonardo da Vinci in 1493, but it was another 450 years before the first practical helicopter took to the air.

Unfortunately for Leonardo, Newton had yet to formulate his Laws of Motion (published only in 1687). According to his 3rd law (action and reaction are equal and opposite), in forcing its rotor blades to turn, the engine of a helicopter necessarily applies and equal and opposite turning force on its body. So nearly all helicopters have a tail rotor to counteract that turning force. If a helicopter looses its tail rotor it spins out of control - the chances of surviving such an accident are virtually zero.

Just a few helicopters and nearly all drones and flying toys counteract the turning force in a different way. They have two or more rotors spinning in opposite directions. The Boeing Chinook is an example. Some helicopters and many toy ones have two counter-rotating rotors on the same spindle. Quadcopters have 4 rotors but you can have any number, provided its an even number, and you make half of them spin one way and the others the other way in order to balance out the twisting force.

A great advantage of having multiple rotors is that you can manoeuvre your drone simply by deliberately unbalancing them slightly. Applying slightly more power to the two rear rotors of a quadcopter causes it to tip forward and start moving forward. You can do the same with the rear two to make it move backwards, or two side rotors to make it move sideways. Equally, you can apply slightly more power to the two clockwise rotors to unbalance the twisting forces and make it turn anticlockwise, or vice versa.

Legal

Legal restrictions on the use of airborne devices such as drones will vary from one country to another.

• In the UK you need a licence if your device is over 250g. See Drones: how to fly them safely and legally.