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  • This is a quadrotor

  • It's called a quadrotor because it has four propellars that spin & generate thrust

  • This is the pilot controlling a vehicle with a radio transmitter

  • That's pretty neat.But if we take a short trip across the street

  • Of course looking both ways before we cross

  • We come to this place for this quadrotor can fly by itself

  • without any human help at all

  • We don't even need a pilot

  • This flying robot can operate with extreme precision

  • in tight indoor spaces

  • It can do some other pretty neat stuff as well

  • So if you're wondering how to make robots fly

  • You've come to the right place

  • Indoor Flying Robots!

  • A crash course

  • Maybe crash course isn't the right term

  • Indoor Flying Robots!

  • An expedited learning experience

  • To figure how to make robots fly

  • we'll need to understand the basic physics of quadrotors

  • How humans pilot them

  • How we can use a computer to achieve the same task

  • And why the resulting flying robots can do more complex things

  • First let's take a quick look at the physics behind

  • how the quadrotors fly

  • When the propellers spin they push downward on the air around

  • Newton's third law tells us that the air applies in an equal & opposite

  • reaction force on the propeller.When this lifting force

  • equals that of gravity the quadrotor achieves hoverfly

  • In order to bank one propeller spins slightly faster

  • than the opposite one

  • This introduces a horizontal force in addition to the one opposing gravity

  • And the vehicle moves sideways

  • That's great, but it didn't tell us how the quadrotor

  • can rotate about it's vertical axis

  • It turns out that newton's third law also applies to rotational force

  • called 'Torque'

  • When this two propellers spin they apply a torque to the air

  • in the clockwise direction. The air applies in equal and opposite reaction torque

  • pushing the vehicle in a counterclock direction meanwhile the other two

  • motors spin in the other direction plus the reaction torque

  • pushes the vehicle clockwise

  • When all four motors are turned on the rotational force

  • remember they are called 'Torque' s -balance each other

  • In flight the vehicle turns by spinning two motors even so

  • slightly faster than the other two

  • That went on the basic physics of how quadrotor flies

  • But before we can fly it robotically we need to know

  • how to control it. First let's figure out how a human would do that

  • The task can be broken down into four keysteps

  • First, the pilot uses his eyes to observe the vehicle

  • and figure out where it is and in which direction it's pointing

  • In this example let's say the pilot see is the quadrotor is sinking

  • Next, the pilot has to decide what control commands to give the vehicle

  • In this case, the pilot has to stop the vehicle from sinking

  • And thus decides to increase the speed of all four propellars

  • To tell the quadrotor what is decided on the pilot uses a radio transmitter

  • which is basically a fancy remote control

  • Finally the quadrotor listens for the radio commands

  • and adjust the speed of each motor accordingly.

  • Now let's see how each of these forces have to change in order to

  • fly the quadrotor robotically

  • In the first step, we use specialized cameras for vision

  • and set up the pilot's eyes. The camera shine infrared light

  • which bounces off of more reflective markers on the vehicle

  • and go back to the camera

  • A camera from the side point of view can tell how far the marker is

  • in the vertical direction and one horizontal direction

  • And a camera from the top point of view can tell how far the marker is in both

  • horizontal directions. Using some slightly more complicated mathematcs

  • we can use the points of view from 12 different cameras

  • To determine the exact three dimensional position of the markers

  • This process is executed many times for second to track the position

  • of the markers and pass the quadrotor in real time

  • In step two, we use a computer to handle the control commands

  • in stead of the pilots brain. The computer program consists of a

  • couple hundred lines of C++ code written by grad students

  • who really don't get out much. It does essentially the same thing

  • as the pilot using the observed position of the quadrotor to evaluate

  • control commands. Only it does so in a much faster and less dramatic fshion

  • In step three, the system uses a similar radio transmitter except a smaller one

  • without any switches or control sticks.

  • Step four is exactly as the same as before. The quadrotor listens for

  • radio commands and adjust the speed of each motor accordingly.

  • So we've updated all four steps in order to make the quadrotor

  • fly entirely by itself. Now all we need is for our grad students

  • to press the go button and voila. One of the reasons the robot

  • fly more precisely than the human pilot is because this loop of information

  • called a 'Feedback Control Loop' can be executed much more quickly by computers

  • In this case 200 times per second. This allows the researchers

  • to do cool things with these indoor flying robots. For instance,

  • fly six of them at once but why not ten

  • They can teach the vehicles how to switch out their old batteries

  • for new ones automically or stop propeller for swing

  • They can even do flips like this one or this one or this one

  • And the fun doesn't stop with quadrotors. The same technology

  • can be applied to rig the shape into three wing aircraft. One more

  • conventional fixed wing vehicles like this one, this one and this one

  • that can even fly in loops. Well hopefully you've learn the basics of how to make

  • robots fly. This concludes the crash course--I, I mean the expedited learning experience

This is a quadrotor

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