Drone Fundamentals

Name: How a Quadcopter Works - Flight Mechanics, Components, & Sensors (2)
Uploaded: 2026-03-07T13:55:08.160170+00:00
Channel: EngineersEscape
Description: Drone Fundamentals A drone is also called a UAV (Unmanned Aerial Vehicle), an aircraft piloted by remote control or onboard computers.

EngineersEscape

Mar 07, 2026

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3 min read

YouTube video ID: u-LfLW9Kgis

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A drone is also called a UAV (Unmanned Aerial Vehicle), an aircraft piloted by remote control or onboard computers. When the drone is considered together with all of its supporting equipment—radio, goggles, and other accessories—it is referred to as a UAS (Unmanned Aerial System). The spinning components that generate thrust are called rotors; in a multirotor they are the propellers. A quadcopter is a specific type of multirotor that has exactly four propellers.

Aerodynamic Forces

The three primary forces acting on a quadcopter are thrust, lift, and weight. Thrust is a pushing force that can act in any direction, while lift opposes the weight, which is the pull of gravity on the aircraft. Torque is a twisting force that tends to cause rotation. Newton’s third law—“for every action there is an equal and opposite reaction”—applies to torque: when a propeller spins one way, the body tries to rotate in the opposite direction. Helicopters solve this with a tail rotor; quadcopters balance torque by using pairs of motors that spin in opposite directions.

Quadcopter Mechanics

In the common “X” configuration, motors 1 and 4 spin clockwise (CW) and motors 2 and 3 spin counter‑clockwise (CCW). This arrangement lets the torques from opposite‑spinning rotors cancel each other out, keeping the craft stable. Hovering occurs when all four motors run at about 50 % throttle, producing equal RPMs so that total lift equals weight and opposing torques neutralize each other. To ascend, the pilot increases throttle on all motors equally, creating lift greater than weight; to descend, throttle is reduced equally.

Pitch (forward or backward tilt) is achieved by increasing RPM on the rear motors while decreasing RPM on the front motors, turning some lift into forward thrust. Roll (left or right tilt) works by speeding up the right‑hand motors and slowing down the left‑hand motors, converting lift into sideways thrust. Yaw (rotation about the vertical axis) is controlled by making the CW motors spin faster than the CCW motors (or vice‑versa), generating an unbalanced torque that rotates the craft left or right. The right stick on the radio controls pitch (up/down) and roll (left/right), while the left stick controls yaw (left/right).

Unmanned Aerial System (UAS) Components

Flight Controller – the “brain” that maintains stable flight and communicates with every other component.
Radio Transmitter & Receiver (RX) – the transmitter sends pilot commands; the receiver passes them to the flight controller.
Electronic Speed Controller (ESC) – receives signals from the flight controller and regulates motor speed; typically one ESC per motor.
GPS/Compass Module – provides location and heading data to the flight controller.
First‑Person View (FPV) Camera & On‑Screen Display (OSD) – captures live video and overlays flight data.
Video Transmitter (VTX) & Video Receiver (VRX) / Goggles – wirelessly send the video feed to the pilot’s display.
Digital Video Recorder (DVR) – optional device for saving footage.
Battery – supplies power; an example voltage is 11.4 V.
Capacitor – smooths power signals to prevent interference.
Power Distribution Board (PDB) – routes battery power to all components and can step down voltage (e.g., from 11.4 V to 5 V or 3.3 V).
Battery Charger – charges the battery and can place it in a storage mode.
HD Camera & Gimbal – high‑definition video capture; the gimbal stabilizes the camera and can be controlled via the receiver.

Drone Sensors

Inertial Measurement Unit (IMU) – combines an accelerometer (measures linear force/acceleration) and a gyroscope (measures rotational motion).
Barometer – measures atmospheric pressure; because pressure decreases with altitude, it is used to estimate the quadcopter’s height.
Voltmeter – monitors battery voltage.
Current Sensor – measures current draw; together with voltage it yields power (Current × Voltage) and can be used to calculate energy consumption in Watt‑hours or charge used in milliamp‑hours.
Compass / Magnetometer – senses Earth’s magnetic field to determine heading (North, East, South, West).
GNSS (Global Navigation Satellite System) – includes GPS (United States), GLONASS (Russia), and Galileo (Europe); provides position, speed, and, to a lesser extent, altitude from satellite signals.

Takeaways

A UAV (drone) and a UAS differ in that the UAS includes the aircraft plus all supporting equipment such as radio and goggles.
Thrust, lift, weight, and torque are the core forces on a quadcopter, and Newton's third law explains how opposite‑spinning rotors cancel torque.
Hovering is achieved at roughly 50% throttle with equal RPMs, while pitch, roll, and yaw are controlled by adjusting motor speeds in specific pairs.
The flight controller acts as the brain of the drone, coordinating inputs from the radio, GPS, ESCs, and sensors to maintain stable flight.
Sensors like the IMU, barometer, and GNSS provide essential data on orientation, altitude, and position, enabling precise autonomous operation.

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Full Transcript YouTube

hi welcome back to engineers escape my
name is Jake and today or on part 2 of
our build a camera drone series how it
flies flight mechanics and components of
a quadcopter unmanned aerial system
let's go
[Music]
if you haven't already make sure you
check out part 1 the introduction and
overview and also be on the lookout for
part 3 where we're going to be ordering
the components before we start building
our quadcopter it's a good idea to have
some basic understanding of how I work
so let's go over to the white board and
get started so what is a drone a drone
could also be called a UAV which stands
for unmanned aerial vehicle an aircraft
piloted by remote control or on-board
computers so we know what a UAV is what
is a UAS UAS stands for unmanned aerial
system so basically includes the drone
and everything else like the radio and
the goggles
what's a rotor a rotor is a generic term
for something that spins or rotates in
our case they will be the propellers
that will create thrust and lift so
what's a quadcopter a quad quadcopter
quadrotor is a specific case of a multi
rotor that has four propellers thrust
lift and torque
thrust thrust is a pushing force and can
be acting in any direction lift is a
force that directly opposes the weight
of the aircraft so gravity will try and
bring it down the force of weight and
lift will keep it up in the air torque
is a twisting force that tends to cause
rotation and I think people might not
have as good of an understanding of
torque as they do these other two so
let's talk about that a little bit more
Newton's third law says that for every
action there is an equal and opposite
reaction an example of this would be
holding an eraser for every action the
weight of the eraser pushing down on my
hand there is an equal and opposite
reaction by hand pushing up on the
eraser and this keeps it still Newton's
third law also works for torques in this
example we have a top-down view of a
helicopter have you ever thought about
why a helicopter has a tail rotor in
this example the propellers are spinning
this way
that is the body is applying a
rotational force on the propellers this
way so according to Newton's third law
the propellers will also be rotating the
body the opposite direction so the body
is going to want to try to rotate this
way this is why we have the tail rotor
the tail rotor will apply a force to the
body of the helicopter to prevent it
from spinning this concept of torques
and balancing is going to be important
in understanding how the quadcopter
works the rusts lift and torque are all
generated by spinning rotors more rpms
create more thrust and torque for each
rotor for simplicity we are going to be
ignoring drag we're going to assume that
the center of gravity CG is centered on
the craft and we're going to assume that
the quad is not moving at the start of
all maneuvers or the velocity equals
zero this is our quad X setup so here
are our four motors you'll notice
they're numbered 1 2 3 & 4 also notice
that the red arrow in the middle is
facing towards the front of the quad
you'll also see the directions that the
propellers are spinning so Motors number
4 and number 1 spin clockwise and motors
number 2 and number 3 spin
counterclockwise also note that the
radio we're using is going to be a mode
2 radio the first move we'll talk about
is hovering hovering means it's staying
in the same place in the air and we're
going to assume at a 50% throttle that
our craft will be hovering the amount of
RPMs each of the propellers is getting
is going to be denoted by the fraction
of the circle that's filled in with
green each of the four motors are at 50%
rpm the important thing about hovering
is that a total lift generated by all
four propellers is equal to the amount
of weight of the copter the quadcopter
will also not be rotating in any direct
because the two clockwise motors are
going the same speed as the two
counterclockwise motors cancelling out
the torques to ascend you'll increase
the throttle to all four motors equally
this will make the lift greater than the
weight and the craft will rise into the
air to descend you'll do the opposite
pitch means when the copter tilts
forward or backwards in this example
we're going to have the copter pitching
forwards so if we look over here at our
diagram the front two motors have spun
down and the back two motors have spun
up since the two back motors have a
greater lift than the front
this will cause the craft to tilt
forwards again the torques in this
example also equal out so we will have
no yawning
since the quad is now tipped forward
some of the lifts will be changed into
forward thrust and propel the quad
forward in order to pitch the craft
forward use the right stick and push it
upwards to pitch back use the right
stick and push backwards roll means to
tilt the copter left or right in this
example we're going to be showing left
roll you can see here that the left two
motors have spun down and the right two
motors have spun up the right two motors
will be creating more lift than the left
two motors this will cause the quad to
roll left
and again the torques cancel out now
that the quad has rolled left some of
the lift will be changed into thrust and
cause the quad to travel to the left in
order to roll we're going to be using
the right stick you push that left to
roll left or right to roll right yaw
means to change the direction at the
front of the craft is facing so you
could lot yaw left or y'all right
in this example we're going to be on to
the left the two counterclockwise motors
are spinning slower than the clockwise
motors this creates an imbalance in
torque and if you remember from Newton's
third law if these ones have more torque
and they're spinning this way then that
means the body is going to want to try
to rotate the opposite way and this will
cause the body to yaw to the left to yaw
to the left push the left stick to the
left to y'alright push the left stick to
the right now let's look at the drone
components in the unmanned aerial system
the flight controller is the brain of
the drone it keeps it in the air and
also talks to other components the radio
transmitter or the remote control will
send our commands from here over to our
receiver abbreviated as our X and that
will tell the receiver will tell the
flight controller what we want to do the
electronic speed controller or ESC takes
the signal from the flight controller
and tells the motor how fast to spin
there are four esc s and motors on a
quadcopter but for simplicity I'm only
drawing one the GPS usually also has a
compass module this sends location data
to the flight controller and also
heading data the first-person view
camera will take video from the
quadcopter in real time and send it to
the flight controller which has a
built-in on-screen display what the
on-screen display does is it takes
flight data and overlays it on the video
so we can read it in real time it takes
this video with the overlaid information
and sends it to the video transmitter
which transmits it through the air which
is received by a power VR X or video
receiver also known as goggles so that
we can monitor it you can also have a
DVR or digital video recorder if you
want to save that real-time footage the
battery supplies the flight controller
and other components
of power this little guy right here is
the capacitor the capacitor cleans up
dirty power signals to prevent
interference this flight controller
doubles as a power distribution board or
PDB and what that means is that instead
of having to solder all the components
power to one pad
there's spats throughout the flight
controller to make it easier to solder
what it also does is it takes the
battery voltage say eleven point four
volts and will reduce it down to
different voltages for these smaller
components such as five volts and maybe
3.3 volts when the battery needs
recharge
we'll put it on the charger the charger
also has another task which is putting
batteries in storage mode and we'll talk
about that more later on our drone we're
also going to have an HD camera and a
gimbal the gimbal stabilizes the HD
camera footage an HD camera of course is
the video we're going to be showing
everyone that looks nice we can also
control the gimbal by hooking it up to
the receiver we now have a basic
understanding of some of the components
so let's talk about some of the sensors
that help the quad fly the first sensor
is the IMU or inertial measurement unit
this actually has two different sensors
one is the accelerometer which measures
the force exerted on the quad the linear
force the next is the gyroscope which
measures the rotational motion of the
quad these two sensors only measure the
linear and rotational forces on the quad
in other words it doesn't currently know
where it's at and it also doesn't know
where it's currently rotated it doesn't
know if it's straight up and down or
upside down with those sensors barometer
is the next sensor a bar is a unit of
atmospheric pressure so this measures
that miss feared pressure since
atmospheric pressure decreases with an
increase in altitude the barometer is
actually used to tell us the altitude of
our quadcopter the volt meter is used to
measure the battery voltage the current
sensor measures
the current power equals current times
voltage or if you want to think of it in
terms of units watts equal one amp
times one volt if you keep track of the
power used over time you can also
display watt hours which will tell you
how much energy has been used from the
battery or milliamp hours which will
tell you how much charge has been used
for the battery the compass or the
magnetometer works by sensing Earth's
weak magnetic field and that will tell
us the heading of the drone in other
words if it's facing north east south or
west GNSS stands for global navigation
satellite system this includes GPS from
the United States and also GLONASS from
Russia and there's also some other
smaller ones like Galileo people usually
call the GNSS just GPS because that's
the one that's typically included and
ours will have receivers for both GPS
and GLONASS based upon its position of
multiple satellites in the sky we can
determine our position speed and to a
lesser extent our altitude all right
guys I hope you found that video helpful
if you did I'd appreciate it if you left
a like and if you'd like to see more
videos like this be sure to subscribe
also if you haven't already be sure to
check out part 1 the intro a no review
and be on the lookout for part 3 where
we're going to be ordering the
components thanks for watching
[Music]