ChopperAddict's Multi Rotor area




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Welcome to this new area of my helicopter web site. This area is totally aimed at Multi Rotor Aircraft (MRC's) such as Quads, and MRC's with 6 and 8 and more propellers.

If you are reading this you may already know about MRC's, or you may just be trying to find out about them, so if you are a bit of an expert in this arena, please feel free to jump straight through to the more advanced parts of this fascinating section!

The rest of you sit down comfortably and pay attention, I am going to try to tell you exactly what MRC's are all about, and clarify some of the more common terms you will probably have encountered already.

Firstly all MRC's come in a similar shape depending on the number of motors/propellers they have fitted. The most popular Quad layout is simply a central hub with 4 legs coming out of it at 90 degrees to each other.  The motors are mounted outboard as far out along the leg as possible, pointing upwards, and are fitted with aircraft type propellers that are of course, horizontal to the ground/horizon. Because each MRC has a notional front and rear, there are two separate configurations used, and that is the X configuration, where the front is directly between the two front arms, and the + configuration, where a single arm is the front and the other end of that same arm is the rear.


The orientation is important because the propellers used are different, two of them being pusher propellers, the other two being puller propellers.  The are arranged so that at the front, you have one of each, and the same at the rear. As you can see from the diagram below, they are arranged so that each of the legs have propellers going in the same direction on each end of the leg. This diagram shows a + configuration MRC 

The central hub is a very important area, as that is where all of the electronics to make the MRC fly will be mounted. All MRC's fly in a very similar way, and this way of flight is rather unnatural to us at first, and I will try to explain why.

Due to the design and layout of the components it is quite obvious that an MRC is more of a Helicopter than it is a Fixed Wing aircraft, and that is certainly very true, BUT The MRC is considerably easier to learn to fly than the Helicopter, which is famous for being very difficult to hover.  The trick is of course in the electronics.  Every quad has some form of "black box" that is the brain of it. They are often called the IIM (Intelligent Information Manager) and there are several manufacturers of them. I do not want to push commercial names any more than necessary so will only mention them when necessary.

The DJI NAZA IIM (brain) controller fitted to an MRC

The most basic IIM has the ability to sense and control altitude to a reasonable degree, and also contains three separate gyros that between them are able to keep the MRC level, and control each of the 4 propellers separately to make the MRC move in any horizontal or vertical (or both) direction, and to make it spin about it's own axis (YAW). The way it is controlled by the pilot is very similar to an RC helicopter.  The throttle stick still controls motor speed, and therefore lift, and also the ability to make the MRC rotate around it's own central axis (YAW). The right hand (CYCLIC) stick is the smarter one of the two, and is used to actually make the MRC go in whatever direction you want it to go. So to go forward, you simple increase throttle/lift to get the MRC to the height you want and then gently push the right (cyclic) stick forward until the MRC starts to move as you want it to.  The major difference between the MRC and a Helicopter is that a helicopter is inherently unstable, so when you bring a helicopter off the ground and up into a hover, it constantly tries to fall over, so you have to work at it all the time to keep it hovering level.  The MRC on the other hand is inherently stable, so when it lifts of the ground and the cyclic stick is centred, it will just sit there.

So much for the basics of the MRC, and you might be wondering what all the fuss is about as it sound as though anybody can fly an MRC, so what is so interesting about them ?


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