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


Drones are available many sizes and shapes, however what we frequently see as multi-rotors are easy drones with 4 motors and propellers, often known 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 correct quantity to supply first rate thrust to raise it up and fly, create a steadiness with an acceptable 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 will we find out about them

Drones, often known as UAVs, are flying gadgets that may be managed through a radio transmitter or can fly autonomously.

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

Propellers might be wherever from 2 to five blades, however this may range. What we frequently discover on customary 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 related 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, hold the drone well-balanced, and optimize energy effectivity.

A drone’s motor might 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

A fair 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 secure 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 models, GPS, and downward imaginative and prescient sensors play a vital function 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 accumulate. If lower than 4 propellers are used, we’re unstable flights and motors over-forcing to generate raise.

Each drone is rigorously 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 steadiness, some drone motors and propellers should overforce themselves and generate additional raise to enhance steadiness, which isn’t ideally suited and should have an effect on a drone’s flight.

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High-quality management of a drone

Controlling a drone comes from the four-axis radio transmitter joystick enter, which sends the sign to the drone through 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 steadiness when flying.

Now, let’s put this into observe.

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 start out 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 can create an imbalance the place the drone will flip in a single course or one other, relying on the place you need 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 roughly than 4 motors, there would now not be excellent concord between the enter of the radio sticks, and the flight controller must do extra 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 excellent stability and positive management of a drone as we now have with four-propeller quadcopters.

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Energy effectivity

With nice energy, we now have nice thrust.

And that’s one way or the other true.

However when it comes to energy effectivity, every drone’s motor pulls numerous energy from the battery, being the principle shopper 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 meant.

For example, a 6-propeller drone, often known 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 now have now.

It’s like an infinite cycle.

That’s why quadcopters – drones with 4 motors and 4 propellers – take advantage of sense when it comes to aerodynamics, positive management, steadiness and stability, and energy effectivity.

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

Due to this fact, you will need to do not forget that quadcopters have an optimum power-to-thrust ratio with 4 propellers that may be tough to acquire in another configuration.

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Following a standard design

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

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

After all, 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 circumstances the place know-how was invested into growing and researching hexacopters and drones with greater than six propellers that would serve distinctive circumstances.

These varieties of drones are very massive in dimension, typically weighing greater than 20 kilograms (the place customary quadcopters are often between 250 grams and 1kg).

4 motors and propellers are usually unable to generate sufficient thrust to raise most of these massive drones, and even when they may, they must be of outstanding 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 after 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 hold all the pieces in steadiness.

If we’re some people-lifting drone designs, we are able to see that a few of them have 6, 8, 12, or much more arms.

However right here’s the factor. In lots of eventualities, we now have two motors with two propellers on every arm. One has the function of a pusher whereas the opposite is a puller, so that they work collectively to train almost 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.

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Security measures

We’ve to lift 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’ll do main injury to things, damage folks, or worse. Drone propellers rotating at these speeds may even be deadly.

Moreover, as they’re constructed from inflexible plastic, these propellers should be sturdy sufficient to actually raise a drone, and the heavier the drone, the extra inflexible the propellers should 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 making certain the propellers should not bent or dented.

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

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

However this isn’t at all times the case.

For example, the DJI Avata is thought to have poor propeller resistance, and plenty of have complained that these propellers began to “explode” mid-air, inflicting the speedy crash of the Avata. Personally, with this particular drone, I at all times go together with dependable third occasion propeller choices.

How do drone propellers spin?

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

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

Picture 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.

Nevertheless, reverse propellers should 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 received’t fly.

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

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

It might 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 an excellent variety of propellers to generate raise and steadiness the drone correctly.

» MORE: How Lengthy Drone Propellers Final?


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