Frame

Frame

The Chassis is the basic structure of a multirotor where all other parts are connected to. Think of it as two parts: a "core" and the "arms" where the rotors are attached. The core houses most of the electronics and protects it from crashes. Also you usually find the center of gravity there.

What materials are used to build a Chassis?

A chassis can be build from a lot of different basic materials and is often constructed with a mix of wood, plastics, metal (Aluminum), fiberglass, carbon fiber and others. Then there are screws and zip-ties to hold everything together and often some kind of flexible foam or similar to dampen vibrations.

To a beginner wood seems to be a great choice. It's easy to work with and cheap. Many kits come with plastic parts. If you own a 3D-printer you can probably print those yourself. Glass fiber and carbon fiber are quite strong and light, but more difficult to work with.

What multirotor models are there?

The form of the multirotor is defined by the number of the rotors and the orientation of the arms.

• 2 rotors
  Twincopters, Dualcopters or Bicopters have two rotors. They can be arranged on top of each other or side by side. Those are the simplest ones, but they are difficult to tune and fly and can not carry a lot of weight. If a motor stops the copter accelerates with about 9,81 m/s^2 in the general ground direction. Some people call that "landing". These types of multirotors are basically never used as they are too unstable.


• 3 rotors
  Tricopters usually have two arms to the front and one to the back. So they look like a T or a Y. The rotor in the back is pivoted using a servo to make the copter rotate on its yaw axis. They can lift more than a twincopter, but not much. If a motor stops the copter crashes. But then these models are very agile.


• 4 rotors
  Quadcopters once again can carry more than a tricopter and are easier to build because they don't need a pivoting servo. They are more stable and can have longer flight times because you can carry bigger batteries. Quadcopters yaw by reducing the speed of two motors so the torque of the other two makes the copter rotate on its yaw axis.
  
  
  
  • QuadX or Quad+ have arms that looks like an X or a +. They differ mainly in where the "front" is.
  
  
  • H-Quads look like a - well - H
  
  
  • Quad V-Tails are a mix between Tricopter and Quad. The back two rotors are closer together and are mounted in a 30-55° angle to the inside or outside. This allows for a much bigger yaw-authority.
  
  
  • There are other rarely used configurations with 4 rotors like a Y4 which looks like a Tricopter but instead of a pivoted motor in the back it has two motors above each other (coaxial), rotating in different directions.
  
  
  
  


• 6 rotors and more
  Hexa-, Octo-, Hexadeca- or Hecatommyriacopters all are based on the same basic design pattern. The rotors are mounted around a central point - usually in a circle. Some models have motors that are mounted on top of each other. A Y6 is an example that looks like a Tricopter, but doesn’t have a tilting mechanism in the rotor. Instead the yaw is done by changing motor speeds just like in Quadcopter. In comparison the yaw feels “sluggish” compared to a mechanical yaw design.
  More rotors result in a bigger lifting capacity and more stability in flight. Those copters can - depending on the controller - survive one or more motor blackouts without losing the ability to fly. But of course the total weight adds up just as the complexity of the build and its price tag. A lot of motors also require a lot of power that needs to be carried in the form of batteries.

Deciding what kind of model to build depends mostly on what you want to do with it. You will probably not mount a camera that costs $ 3000 or more on a tricopter (if it lifts it at all). And you probably will not do acrobatics with an octocopter.

For a beginner quadcopters seem to be a great solution. They are easy to build and can be very stable. But when you are just starting, make sure you follow this tip: Keep it simple, keep it light.

Don't start with a fully equipped system. First of all it will hurt a lot more if you crash with expensive equipment. Second: A light system is easier to control and keep in the air. Third: you will not learn how to fly a multirotor if the controller (see next post) does all the work for you by self-leveling and staying at a programmed position. Learn how to handle a simple multirotor first, then proceed to the next level.