The RC quadrocopter, also called the quadricopter, quad rotor RC helicopter, or multi-rotor is the latest development in radio controlled vertical lift platforms that are able to take off vertically, hover, and fly in all directions. As the name suggests, there are 4 propellers arranged in a cross type configuration.
There is no single large collective pitch rotor or tail rotor that we are all used to seeing on a conventional RC helicopter. These propellers are fixed pitch, two will spin clockwise and the other two will spin counter clockwise. By precisely and accurately spinning these four propellers at different speeds, all the common directional movements of a standard helicopter are attainable - Hover, forward/backward movement, left/right movement, and yaw (turn rate) movement.
There are certainly other incarnations of the quadrotor design using as little as 3 propellers arranged in a triangle configuration up to six arranged in a hexagonal configuration and even eight (Octocopters); but for ease of explanation, I will stick with the quad variety as it is the most common and if you do end up getting this type of RC helicopter, most likely what you will be starting out with.
How Do They Work?
The reason RC quadrocopters are fairly new on the scene is the complex and rather heavy computing/processing power required to accurately control these 4 propellers to not only move the heli about, but to keep it stable. Inherent stability as I mentioned is very good, but directional control stability was the single largest hurdle that had to be overcome and only because of today’s solid state gyro and accelerometer technology, efficient and fast responding brushless motors, coupled with small micro processors to deal with the hundreds of calculations and control commands every second, can these things fly at all. RC quadrocopters are not that performance minded and certainly are not capable of any fancy aerobatics mostly due to the very taxing computing power to just keep them airborne and the fact they use fixed pitch propellers making sustained inverted flight impossible. Times are changing however as lighter and more efficient processing power and electronic sensors become available making some fairly aggressive 3D flight possible and accurate – have a look at this video and you’ll see what I mean.