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