Wednesday, 9 September 2015

Multi Rotors Part 1 - Introduction

  • RC- Multi rotor aircrafts are the fastest developed and still developing vertical lift aircrafts that are able to  hover and fly in all directions.
  • These aircrafts are not like a conventional RC helicopter. The propellers are fixed pitch and spins clockwise and counter clockwise.
  • By precisely and accurately controlling the spinning speed of propellers , all the directional movements are achieved ( hover, forward/backward movement, left/right movement, yaw (turn rate) and up-down movement).
  • The multi rotor RC aircrafts are mechanically very simple with hardly any moving parts compared to mechanically complex collective pitch or  fixed pitch RC helicopters and airplanes.
  • This also makes multi rotor RC aircrafts an  easy machine for RC hobbyists to custom build their own aircrafts. All that needed are  frame, motor, ESC, propeller, Tx-RX and flight control/ stabilization board, along with LiPo battery.
How the Multi Rotor Aircraft works?
  • The reason RC multi rotors are fairly new in the field of RC Flying is the complex computing/processing power required to accurately control all the propellers to keep it stable. 
  • Multi rotors are most unstable aircraft.
  • Only when all propellers are spinning at the same rate, producing equal amounts of thrust and torque, and experiencing equal amounts of drag is how hovering is achieved.
  • Controlling this manually is almost impossible.
  • By using latest solid state gyros and accelerometers, BLDC motors, coupled with tiny microprocessor based control boards to deal with thousands of calculations and control commands every millisecond, then only we can make these machines fly at all.
  • When RC multirotors were first introduced a few years ago, the emphasis was on an easy going and stable flight.
  • But now things have changed , many models are capable of performing aggressive aerobatic flight . In fact, most of the recent hobby grade multirotors are aerobatic these days capable of performing fast flips and rolls and also able to fly easy stable flying mode/s for beginners.
  • In stable modes, the electronics onboard simply won't let the aircraft pitch or roll beyond a certain degree so that beginners can fly it smoothly.
  • The latest generation of mid priced to high end quad rotors are fitted with GPS positioning and many other additional sensors. This gives them fully autonomous flight control, way point navigation, auto take off/landing, position hold, obstacle avoidance and "return to home" capabilities.
  • The level of electronic support available to achieve this is remarkable. The pilot/operator basically just telling them what to do and the electronics and programming capability is fully responsible for the actual flying.
Can we select a Multirotor as a First RC Project?
  • The answer is Yes!
  • This make a wonderful first RC project if you want an easiest flying experience available to start with, at the same time get an exposure to the electronics and programming involved, get some experience with radio control and stick operation, and  later on as your skills improve learn how to do aerobatic performance.
  • Multi rotors, in this especially Quadcopters are for the larger group of people who just want to fly something by radio control and don’t care for a "real" airplane feel or look or sometimes just want one of the coolest and funniest flying machines  around.
  • That is why multi rotors are showing the strongest growth and popularity over all other types of RC aircraft right now.
  • RC-mulit rotors requires complex electronics, so they were very costly in the beginning,  but again as mass produced electronics and miniaturization becomes more and more common place, prices are dropping sharply.
How Multirotors are categorised as per Size?
  • If you look at any multi rotor on the market, most have a size number such as 180,350,450,550,800, and so on... What does this size number indicates?
  • For the majority of multirotors this size means the diagonal distance in millimeters from each opposite motor's center (motor hub to motor hub).
  • But for, Hexa and octa copters they are measured motor hub to motor hub on adjacent motor arms. 
Use of Multirotors
  • Aerial Photography , Aerial Videography and FPV Flying.
  • The real reason behind the multirotor development is their application for the jobs mentioned above.
  • Since these machines can almost fly themselves, hover, have superior lift efficiency, and requires not much skill to pilot.
  • They have become one of the most popular vertical lift and flying platforms for different aerial photo, video, and FPV applications from armature, policing, research to sporting events, public function, military application to wildlife and nature.
  • With the advancement of electronic sophistication and on-board autopilot systems providing a very stable and GPS assisted pinpoint fixed position control, hands off hover,  they give the freedom and ability to the operator/pilot the concentrate fully on camera monitoring or data analysis .
  • We need not to spend big money these days to get a quad rotor with basic aerial photographic capabilities.
Types of Multirotors.
  1. Tricopter: This is the basic one of multi-rotor family. This is one of the easiest and cheapest to build. But when we comes down to performance its motors undergo most strain because they are running on a higher throttle all the time when comparing with other multirotors leaving it with low flight time and low lift capabilities.
  2. Quadcopter: This is the most popular in multi-rotor family. This is little more challenging and more expensive to build. The quadcopter is little heavier than tricopter with the extra motor but that extra motor gives the quad an extra boost in lift capacity and flight time. For these two types, if a motor fails the whole aircraft will crash.
  3. Hexacopter: This design is in-between a quad and an octacopter. This is little more  difficult to build and more expensive also. But it can carry a much heavier load than the quad, may require more than one battery to achieve the desired flight time as of a quadcopter. The advantage in this design is that, if one of the motors fails we will just lose the yaw control of the aircraft but will be able to stay flying.
  4. Octacopter: The big brother of multirotor family. This one is the most difficult and the  expensive to build. But, it can take the heaviest payload we want on it and can have extended flight time by using two or more number of LiPo batteries (High payload capacity).
  5. There are some more variants in this family as per the positioning of motors and propeller combination. See the picture below.

Coming up next : Scratch building a quad copter. Step by step approach based on my experience of building quad copters.

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