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Saturday, October 12, 2013

Chapter 2: The Quadcopter

Operation of a quadcopter/multicopter is similar to that of a helicopter.  It has a control similar to a helicopter's cyclic control that enables pitching the quadcopter anywhere within its 360o radius.  But the quadcopter differs from the helicopter in that it has no tail boom.  Because of this, the quadcopter can easily fly in any direction regardless of which way its "front" may be pointing.  Thus a quadcopter can change its direction of flight more rapidly than any other flying machine.

The multirotor concept has been around for a long time.  But until recently it wasn't practical as the design is inherently unstable.   Controlling multiple rotors to maintain steady flight is extremely difficult if not impossible for the average person.  But advances in gyroscope attitude sensing technology (thanks to the Wii, tablets, and phones) have developed very small, low-power attitude sensors that can be incorporated with computer logic to automatically balance the quadcopter in flight.  Thus the pilot can now focus entirely on his flying skills, and no longer be distracted to also manually balancing the quadcopter from flipping over.

Currently there are two versions of attitude gyros that you should be familiar with.  They are titled as "3 axis", and the somewhat incorrectly titled "6 axis".  The 3 axis automatically balance the forward & aft tilt (pitch), and right & left tilt (roll) of the aircraft.  The right and left turning axis (yaw) is also steadied by the sensors.  A balanced and properly trimmed (more on trimming later) quadcopter should takeoff and hover relatively motionless in the air.  It should not tilt or turn in any direction until you apply control to the aircraft. Additionally, if you apply and remove control, it should slowly but automatically return to a horizontal non-turning position. 


The 6 axis gyro stabilization provides much faster correction of attitude displacement than a 3 axis system.  In addition to the three pitch, roll, and yaw sensors, three additional accelerometers sense acceleration in the three dimensions.  Now our quadcopter can automatically sense and compensate for sudden wind gusts.  When we provide command to hover our quadcopter (center our pitch controls, called cyclic), the accelerometers can sense if the quadcopter is still in motion and automatically compensate to rapidly achieve hover.  Finally, the six sensors in combination can detect both unusual attitude (if we're flipped upside down) and can also tell if we're falling to the ground.  By centering the pitch controls, and applying throttle, a 6 axis copter will quickly right itself and come to hover.  This last one is really cool and must be seen to be appreciated.

It's obvious that for most beginners a 6 axis quadcopter is the best option as it's most forgiving.  It's even appreciated by more advanced flyers as a 6 axis quadcopter is also very nimble, able to "turn on a dime".  

6 comments:

  1. You claim that a 6 axis quadcopter will quickly right itself and hover but I don't think that's true. If it was, then anyone could easily fly one. I tried some in the hobby store and couldn't get them to hover or fly in the direction I wanted, The store clerk tried and couldn't get them to fly very well either!

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    Replies
    1. They will right themselves when you apply throttle. But steady flight in hover depends on some practice. You mention that you tried one in a hobby store. Would not recommend a hobby store as the first place to start in this hobby. Store clerks are unlikely to have much experience or knowledge as the hobby is still relatively new. Also, you may have been flying an older three-axis quad in the store (not saying that your store may have been unscrupulous, but I have seen this happen in the past). Would instead recommend an inexpensive (under $50) quadcopter to begin with. The only place to find those prices is on the internet.

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    2. the drone will right when applied throttle (as Camera Repair said). in my opinion, I would not start the hobby at a hobby shop(I know, sounds weird to say). The drone you had flied may have not been a new one but a fairly old drone. some hobby shops use old ones and put them in their shops. Myself, I have used amazon to find a quadcopter

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  2. There's a problem with terminology here. You say, "It has a control similar to a helicopter's collective control that enables pitching the quadcopter anywhere within its 360° radius." But a helicopter's pitch and roll are controlled by its cyclic control, which effectively tilts the rotor disk. The overall lift of the rotor disk is controlled by the collective control. Thus everywhere you refer to "collective" in this article, you should be saying "cyclic."

    This Wikipedia article explains helicopter controls:
    http://en.wikipedia.org/wiki/Helicopter_flight_controls

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  3. Just got a Phantom for X-Mas, and a UD839 as a trainer so I don't wreck the Phantom. Old Dawg, new tricks!!! So many questions, and couldn't be happier I found this site. Let the Flight training begin!

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