Modern FPV drone on a black background. Four-engine aircraft on the radio control

Why Drones Have 4 Rotors?

Estimated reading time: 7 minutes

Unmanned Aerial vehicles (UAV) or drones have turned things upside down in diverse industries, including surveying and mapping, transportation, construction, and farming. The one question that stands out is why drones have 4 motors. 

Drones have four motors to enhance maneuverability and hovering ability. The four-rotor design makes the drone relatively simple yet highly maneuverable and reliable. 

A rotor provides thrust to raise the drone from the ground. It gives it attitude and directional control by moving forward, backward, and sideways.

However, quadcopters (four-motor drones) lack the aerodynamic efficiency you find in a single-rotor helicopter. 

What is a quadcopter? Why do some drones have four rotors? What is a rotor, and how does it work?

Here’s all you need to know about quadcopters.

What Is a Quadcopter?

A quadcopter is a drone type defined by its four-rotor design. The rotors are strategically positioned to allow the device to fly and benefit from altitude hold. 

Quadcopters are drones, but not all drones are quadcopters.

Among the small drones, quadcopters are more durable and cheaper due to their mechanical simplicity.

Infographic for quadcopter versus fixed wing aircraft

The Reason Drones Have 4 Rotors:

Four-rotor drones are a section of the multi-rotor drone family. They are the most popular drone type for hobbyists.

Quadcopters were invented because aircraft needed improved maneuverability and hovering ability, which is the primary reason for this drone type’s invention. 

When you adjust speed and direction, the drone’s maneuverability is more precise and remains more stable during flights.

Its four-rotor design keeps the device simple yet highly maneuverable and reliable.

Because of their simplicity, these drones are cheaper and more durable than conventional helicopters. Their small blades have less kinetic energy, minimizing their damage-causing ability. 

What Is a Drone Rotor?

A drone rotor is a component that facilitates a UAV’s propulsion and control. It’s the rotating part of a drone, transferring mechanical power or interacting with a magnetic field to generate electrical power or motion.

The drone component consists of a propeller connecting to a motor.

How Do Drone Rotors Work?

Drone rotors work similarly to fans. Their forces are in pairs, while the rotating blades (propellers) push the air downward. As a result, the air pushes the rotor up —the lift’s basic principle.

Two of the four drone rotors move clockwise, while the other two move anticlockwise for the drone to hover. That ensures the drone’s sideways momentum’s balance.

The first two rotors increase their spinning to avoid throwing the drone’s vertical motion off-kilter.

Similarly, the rotors apply thrust while ensuring the rotor’s spin maintains the drone’s balance.

Multi-Rotor Drones vs. Single-Rotor Drones:

The main difference between multi-rotor and single-rotor drones is the number of rotors. Multi-rotor means more than one rotor. 

In our case, quadcopters have four. Others include tri-copters (3 rotors), hexacopters (6 rotors), and octocopters (8 motors). Quadcopters remain the most popular among them.

Multi-rotor drones are the cheapest and easiest to operate. 

They’re perfect for the following tasks: 

  • Aerial photography and videography 
  • Surveillance in the air
  • Visual inspections
  • Thermal reporting
  • 3D scanning

On the other hand, single-rotor drones have only one rotor —resembling one big spinning wing and a tail rotor for stability and direction control.

Single-rotor drones’ structure and design are similar to actual helicopters. They’re strong and durable.

The technical uses for these drones include the following:

  • Transporting heavy payload
  • Aerial LIDAR laser scanning
  • Surveying 
Multi-Rotor Drones

Image Source

Are More Rotors Better?

Increasing the number of rotors in drones has benefits and drawbacks, including the following:

Benefits:

Higher Lifting Capacity:

Drones with more rotors generate much higher lift, which allows them to accommodate more payload types.

Heavy lifter drones have six rotors or more. This requirement is important when carrying the weight of a DSLR camera or crop-spraying fertilizer.

Multiple payload carriage capability increases the drone’s operational efficiency during flights and reduces inspection time.

drone carrying a parcel

Redundancy:

There are higher chances of recovering a six or eight-rotor drone than a quadcopter. The latter flies out of control and crashes shortly if one of the rotors fails. 

Drones with more than four rotors have at least one redundant rotor. Thus, they stay in the air after one rotor stops spinning.

However, you can’t continue flying your gadget normally. Otherwise, you’ll compromise flight performance, and immensely high power will be drawn from the remaining motor.

Redundancy in multi-rotor drones guarantees the likelihood of recovering your device if things go wrong. The feature is crucial in challenging locations like near electromagnetic interference.

Other benefits include the following:

  • Increases maneuverability: Up and down movement (on the same vertical line), side to side, back to front, and rotating on its axis.
  • Ability to fly closer to buildings and structures.
  • Better aircraft control during flights.

Drawbacks:

Increased Weight and Size:

A multi-rotor drone has more motors, sensors, and a larger frame to shelter the additional mechanical and electrical components. That increases the device’s overall weight.

As a result, propellers generate more lift, consuming more power. Such a drone needs a larger battery, or even two.

That’s what gives quadcopters a higher edge. Some are palm-sized, increasing their portability and reducing power consumption.

Also, the heavy drones have shorter flight times than the lightweight ones.

Higher Prices:

More rotors necessitate additional hardware and engineering, increasing the overall cost and prices. Most drones with more than four rotors are significantly pricier.

Other downsides include the following:

  • Inability to use gas engines due to the fast and high-precision throttle changes demands.
  • Limited endurance and speed render them unfit for large-scale aerial mapping, long-distance inspection, and long-endurance monitoring. 

Parting Shot:

Maneuverability enhancement and hovering capacity are the primary reasons why drones have 4 rotors. The drones’ design keeps them simple but very reliable and efficient.

That maintains the quadcopter family on top of the multi-rotor drone market. 

Commercial drone fliers recognize the four-rotor drone type as one with the ideal mainstream appeal. The drones are highly portable, inexpensive, and easy to fly.

Hobbyists have embraced them as their traveling photography companions for the same reasons. 

Other multi-rotor drones still have their share of the market, but they only suit high-level professional pilots. Although they’re powerful, they’re expensive and unportable.

FAQ

What Is the Purpose of a Multi-Rotor Drone?

A multi-rotor drone is used for widespread operations. Because of its VTOL (vertical take-off and landing) operations, no extra take-off and landing space is required. 

Also, the drone’s ability to hover at one point makes it ideal for specific imaging applications and surveillance missions.

What Is the Main Difference Between Fixed Wing Drones and Quadcopters?

The main difference between a fixed-wing drone and a quadcopter is the ability to hover. The latter can hover in one place while the former can’t. 

It must move continuously throughout the flight. A quadcopter can perform more precise maneuvers, while its fixed-wing counterpart can only make imprecise flyby runs.

How Long Can a Four-Rotor Drone Fly?

A four-rotor drone can fly between 20–30 minutes. Typically, multi-rotor drones fly for at least 20 minutes using a lithium-ion battery, with an exemption for some high-end drones and fixed-wing aircraft. 

You can increase the duration using another fuel source like gas or hydrogen.

Are Tricopters Viable?

Yes, tricopters are viable. The three-rotor drones have a small volume and a more extended battery life than the quadcopters. 

Also, they’re lightweight and have agility in turns and translation. They reduce the actuators that control flights using passively adjusting tilt wings.

Is a Hexacopter Better Than a Quadcopter?

Yes. A hexacopter is better than a quadcopter due to its increased payload capacity and stability. 

The drone suits professional aerial videography, photography, surveying, and mapping. It’s also perfect for crop spraying and monitoring. 

However, hexacopters aren’t pocket-friendly.

HAPPY FLYING!

Summary
Article Name
Why Drones Have 4 Rotors?
Description
What is a quadcopter? Why do some drones have four rotors? What is a rotor, and how does it work?
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Remoteflyer Private Limited
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