Why Do Drones Have 4 Propellers? (Defined for Novices) – Droneblog


Drones are available many styles and sizes, however what we frequently see as multi-rotors are easy drones with 4 motors and propellers, also referred to as quadcopters.

Picture credit score: Gabriel Mihalcea

Why is that? Why don’t we frequently see drones with three, 5, six, or many extra motors and propellers?

For small drones, 4 propellers are the precise quantity to supply respectable thrust to raise it up and fly, create a stability with an appropriate heart of gravity, and assist maneuver the drone easily, in addition to hover constantly. 

However there’s rather more to it, so for those who’re seeking to actually grasp the dynamics of drone flight with 4 propellers, let’s dig in.

Quadcopters: what can we learn about them

Drones, also referred to as UAVs, are flying gadgets that may be managed by way of a radio transmitter or can fly autonomously.

As you would possibly infer from the identify, a quadcopter is made of 4 motors mounted on particular person arms linked to a central body containing the electronics. Every motor has a propeller to generate the thrust required for the drone to take off.

Propellers could be anyplace from 2 to five blades, however this will fluctuate. What we frequently discover on commonplace GPS drones are propellers with two blades.

Because of the distinctive type of every propeller mounted on the drone’s electrical motors, they generate a robust air present in a pusher or puller formation, which is powered by a Lithium (clever) battery.

A drone hosts many electronics, from the flight controller and ESC to sensors like IMU, gyroscopes, accelerometer, compass, and GPS module.

Each part is hosted in a body the place the drone arms are linked and well-balanced in accordance with the variety of propellers/motors a drone has. On this case, we’re speaking about 4 motors.

That is the candy spot to generate sufficient raise, preserve the drone well-balanced, and optimize energy effectivity.

A drone’s motor could be quickly accelerated and decelerated to tens of 1000’s of RPMs (rotations per minute) by the drone’s flight controller.

These quadcopters with 4 propellers work collectively to supply the identical quantity of thrust individually for the drone to take off vertically (VTOL).

Balancing and stability

Picture captured by Dan Bayne; modified in Canva by Gabriel Mihalcea

An excellent variety of motors and propellers on a drone, 4 on this occasion, is the candy spot for the digital flight controller and sensors to work all collectively to supply a well-balanced quantity of thrust for the drone to remain steady within the air.

Within the case of a drone hovering, every motor receives fluctuating currents from the drone’s flight controller for micro-adjusting whereas the drone is flying and hovering stably.

Drone sensors such because the inertial measurement items, GPS, and downward imaginative and prescient sensors play a vital position in offering knowledge in real-time to the flight controller.

If a drone needed to have greater than 4 motors to generate raise, this is able to be harder to amass. If lower than 4 propellers are used, we’re taking a look at unstable flights and motors over-forcing to generate raise.

Each drone is fastidiously constructed and manufactured in accordance with the inner parts to be balanced on the body on the proper level the place the middle of gravity falls. 

If one thing is out of stability, some drone motors and propellers should overforce themselves and generate additional raise to enhance stability, which isn’t best and will have an effect on a drone’s flight.

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Wonderful management of a drone

Controlling a drone comes from the four-axis radio transmitter joystick enter, which sends the sign to the drone by way of the radio transmission system. 

These axes are throttle, yaw, pitch, and roll. See the next picture for a mode 2 radio controller.

Illustration created by Gabriel Mihalcea

As a result of we even have 4 motors and propellers that reply in accordance with the pilot’s radio enter, every motor ought to act individually or as a pair, leading to higher stability when flying.

Now, let’s put this into apply.

The drone’s controller throttle is on the center axis, producing greater than sufficient energy to train liftoff.

You progress the “roll” axis to the left. What occurs right here?

The 2 proper motors train additional thrust for the drone to begin drifting to the left. Micro-adjustments are additionally made to the left motors to take care of the identical altitude.

What about when appearing on the “yaw” axis?

Two reverse motors train additional thrust whereas the 2 different reverse motors train much less thrust. This may create an imbalance the place the drone will flip in a single course or one other, relying on the place you wish to flip left or proper whereas sustaining the altitude. (So the completely different course spinning propellers will readjust their RPM accordingly).

Now, if we had kind of than 4 motors, there would not be good concord between the enter of the radio sticks, and the flight controller must do further calculations in relation to each motor for these actions to be carried out easily.

On this case, we most likely wouldn’t have the identical good stability and effective management of a drone as we have now with four-propeller quadcopters.

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Energy effectivity

With nice energy, we have now nice thrust.

And that’s by some means true.

However by way of energy effectivity, every drone’s motor pulls lots of energy from the battery, being the principle client of energy in a drone. 

The extra motors a drone has, the extra energy it is going to require for the drone to carry out liftoff and fly as supposed.

As an illustration, a 6-propeller drone, also referred to as a hexacopter, would require 50% extra energy than a quadcopter due to the additional motors.

On this case, a bigger battery is required on the hexacopter, which provides weight, whereas the motors will want extra energy to generate additional thrust for the drone to raise off. However it is going to have additional raise due to the 2 additional motors we have now now.

It’s like an infinite cycle.

That’s why quadcopters – drones with 4 motors and 4 propellers – take advantage of sense by way of aerodynamics, effective management, stability and stability, and energy effectivity.

Nonetheless, hexacopters and drones with greater than 6 propellers even have distinctive utilization, which we’ll cowl later.

Due to this fact, it is very important keep in mind that quadcopters have an optimum power-to-thrust ratio with 4 propellers that may be tough to acquire in every other configuration.

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Following a standard design

Since drones have change into broadly obtainable in the marketplace and enormous corporations are investing multi-millions of {dollars} to develop and enhance drone know-how, they’ve all adopted a fundamental drone design – a quadcopter with 4 propellers.

As we have now talked about earlier than, because it makes essentially the most sense to easily develop drones with 4 propellers, this was the trail most drone corporations have adopted as a standard design.

In fact, some have experimented with two-motor drones, three-motor, and much more, however none of them have been as environment friendly as the present quadcopters.

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When are greater than 4 propellers used?

There have been many instances the place know-how was invested into growing and researching hexacopters and drones with greater than six propellers that would serve distinctive instances.

These forms of drones are very giant in dimension, typically weighing greater than 20 kilograms (the place commonplace quadcopters are normally between 250 grams and 1kg).

4 motors and propellers are usually unable to generate sufficient thrust to raise these kind of giant drones, and even when they might, they must be of remarkable dimension, disproportionate to the design and the drone’s aerodynamics.

That’s why, even with the larger energy necessities, drones with greater than 4 propellers are used to carry bigger payloads and, in cinematography, to hold professional-level cinema cameras. 

Furthermore, with extra propellers, it’s simpler for them to alter velocity and maneuver easily once we’re coping with very heavy drones.

Regular drones would most likely by no means be capable of exert this quantity of thrust to generate raise and even preserve the whole lot in stability.

If we’re taking a look at some people-lifting drone designs, we will see that a few of them have 6, 8, 12, or much more arms.

However right here’s the factor. In lots of situations, we have now two motors with two propellers on every arm. One has the position of a pusher whereas the opposite is a puller, in order that they work collectively to train practically double the quantity of thrust per arm with a single motor and propeller.

So, it’s not at all times true that hexacopters have six propellers mounted on six motors. For the additional thrust required, they will have six arms with 12 motors and propellers.

» MORE: What’s a Cinelifter? (Defined by a Skilled FPV Pilot)

Security measures

We’ve got to boost a little bit of consciousness. Drones are harmful if not dealt with effectively, and on this case, it doesn’t matter if a drone has 4, six, or extra propellers.

Every drone propeller can spin at speeds of tens of 1000’s of rotations per minute to generate sufficient thrust to raise the drone.

These drones’ propellers are like blades. They will do main injury to things, harm folks, or worse. Drone propellers rotating at these speeds may even be deadly.

Moreover, as they’re constructed from inflexible plastic, these propellers need to be sturdy sufficient to actually raise a drone, and the heavier the drone, the extra inflexible the propellers need to be.

However at instances, drone propellers can fail even mid-flight, and the drone will face an imminent crash. That’s one thing we can’t management apart from doing a pre-flight guidelines and guaranteeing the propellers are usually not bent or dented.

The extra propellers a drone has, the upper the possibilities of a drone propeller failing mid-air simply because of the larger whole quantity.

That’s why we will say that, usually, light-weight drones with 4 propellers are much less more likely to fail mid-air than heavier drones with greater than 4 propellers.

However this isn’t at all times the case.

As an illustration, the DJI Avata is thought to have poor propeller resistance, and lots of have complained that these propellers began to “explode” mid-air, inflicting the quick crash of the Avata. Personally, with this particular drone, I at all times go along with dependable third celebration propeller choices.

How do drone propellers spin?

In a quadcopter with 4 propellers, you might suppose that every one of them spin in the identical course. However that’s not appropriate.

Let’s take a look on the following picture, lets?

Photograph captured by Dan Bayne and edited in Canva by Gabriel Mihalcea

This picture is solely illustrative, however I hope you get the purpose.

The entrance left and entrance proper propellers can spin inwards, and the identical has to occur with the again left and again proper propellers. This methodology known as “props in.”

However they will additionally spin outwards, additionally termed props out, however that’s not a rule.

Nonetheless, reverse propellers need to spin in the identical course, the other means from the opposite two propellers. In any other case, the drone will flip over when making an attempt to take off, and it gained’t fly.

With six and a number of propellers, that’s one other story. 

And see what can be the difficulty if a drone had three or 5 propellers?

It could be completely unbalanced when flying, inflicting the drone to rotate until, as an illustration, one propeller spins at double the velocity of the opposite two propellers in a tri-copter. It’s simply less complicated to create a quadcopter, although.

That’s why it’s particularly essential that drone designs have a fair variety of propellers to generate raise and stability the drone correctly.

» MORE: How Lengthy Drone Propellers Final?

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