The basic principle of quadcopters relies in four propellers to create lift and give the operator control to change directions. Each propeller has its own motor allowing the propellers to operate at different speeds, this allows you to control the lift, pitch and yaw to change direction by instructing one or more of the propellers to move faster or slower.
To give the quadcopter stability two of the propellers rotate clockwise and the other two rotate counter-clockwise. A Motor Control Unit (MCU) communicates with the four propellers giving the device stability. The most important part of the quadcopter design is its frame. The frame needs to be light enough to allow lift and flight bot durable enough to withstand the occasional unintended crash landing. Quadcopters can vary in size from miniature ones that fit in the palm of your hand up to 25kg.
Most recreational drones will run on Lithium batteries which makes them relatively light allowing them to fly for around half an hour. Serious enthusiast will often carry multiple battery packs as back-ups for when the first ones run out. You are unlikely to be within close proximity to a power source to be able to recharge you battery when it runs out if you’re flying your drone in a nature reserve for instance. There has been research into commercially viable solar drones however they are mostly still in development stages.
In 2015, Atlantiksolar of Switzerland achieved a continuous 4 day flight, covering an amazing 2316 km, with a solar powered drone prototype.
The quadcopters are controlled by a remote control or some can be operated via a smart tablet device. The quadcopter and controller communicate by radio waves or Wi-Fi signal. For security the drones have encrypted computer chips to help prevent hacking from being signalled from another device. Using the control the operator instructs the vehicles separate engines to speed up or slow down to create the desired movement.