Multirotor Drones

What is a multirotor drone?

A multirotor drone is an aircraft that lifts itself with several fixed rotors, each spun by its own electric motor. It has no wings, no tail rotor and no moving blade pitch like a helicopter. It steers by changing the speed of each motor a few hundred times per second.

That last part is what makes it work. A flight controller with a gyroscope and an accelerometer measures tilt constantly and adjusts every motor on its own. Speed up the rotors on one side and the drone leans and moves the other way. Speed up the clockwise rotors against the counter-clockwise ones and it turns on the spot. The pilot only says where to go; the controller does the balancing.

Rotors come in pairs that spin in opposite directions so their torque cancels out, which is why the useful layouts have an even count: four, six or eight. A multirotor is the family name. The members are named by the count: quadcopter, hexacopter, octocopter.

4 rotors6 rotors8 rotors

Quadcopter, hexacopter, octocopter: how they differ

The three share the same idea and the same parts. What changes with every pair of rotors added is lift, safety margin, size and price, in that order.

Four rotors is the efficient answer: the fewest motors that can control an aircraft in every direction, so the lightest, cheapest and longest-flying for its size. That is why every camera drone, toy and racing drone is a quadcopter.

Six and eight rotors are the answer to a different question. They make sense once the thing hanging under the drone is worth more than the drone, or heavy enough that four motors would have to be huge. You pay for that in weight, batteries and price, and you get redundancy in return.

One market fact that surprises buyers: on Amazon.com there are thousands of ready-to-fly quadcopters and almost no ready-to-fly hexacopters or octocopters. Those are sold as frames to build on, or through professional dealers. The table marks every listing as ready to fly or kit so you know before you click.

Quadcopters — 4 rotors

The quadcopter is the drone most people mean when they say drone. Four arms, four motors, two spinning each way. It covers everything from a 30-gram indoor toy to a professional camera platform, and it is where nearly all the choice and all the price competition live.

What separates one quadcopter from another is not the layout but three specs: weight (under or over 250 g, which decides FAA registration), camera (resolution, sensor and gimbal) and flight time per battery. A quadcopter cannot survive a motor failure, but motors on modern brushless drones rarely fail; batteries and pilots are the usual culprits.

All of them, compared by those specs, are on the Quadcopters page.

Under 250 g4K cameraFor kids

Hexacopters — 6 rotors

A hexacopter adds two arms and two motors. The extra thrust lets it carry a real camera, a mirrorless body with a lens on a three-axis gimbal, and the extra motors give it a chance to land safely if one of them stops.

The classic hexacopter is a DIY build on a frame between 550 and 900 mm, running open flight software such as ArduPilot or PX4. That is exactly what Amazon.com sells: frames from Tarot, JeeFly and similar makers, some with motors included, to which you add electronics, a radio and batteries.

Frames, prices and what each one includes are on the Hexacopters page.

Octocopters — 8 rotors

Eight rotors is the heavy end of the family. Octocopters lift cinema cameras, crop sprayers, LiDAR scanners and delivery payloads, and they are built to keep flying after losing a motor, sometimes two.

They come in two layouts. The flat octocopter has eight arms in a star, is large and efficient. The coaxial X8 puts two motors on each of four arms, one above the other, which makes it compact and easy to transport at the cost of some efficiency.

On Amazon.com an octocopter is almost always a carbon frame of 1,000 mm or more, sold for builders and professionals. They are on the Octocopters page.

Payload and flight time by rotor count

More rotors do not mean longer flights. They mean more lift, and the lift gets spent on carrying things. The rough numbers for complete, ready-to-fly aircraft look like this:

The rule behind the table is simple: flight time depends on how much of the available thrust you are using. A heavy-lift octocopter flying empty can hover for a long time; the same aircraft with a cinema camera under it may land after twelve minutes. Makers usually quote the empty figure, so read it as a ceiling.

For a build, aim for a total takeoff weight of no more than half the maximum thrust of all motors combined. That leaves room to climb, fight wind and, on six or eight rotors, survive a motor failure.

Over 25 minutesHeavy lift

Redundancy: why more rotors means safer flight

This is the whole argument for more rotors, and no product listing explains it.

A quadcopter has no spare motor. Each one is needed to balance the other three: lose one and the drone can no longer hold its attitude and heading at the same time, and it falls. Some research firmware can bring a quad down spinning in a controlled way, but no consumer drone relies on that.

A hexacopter usually survives losing one motor. The flight controller notices the missing thrust and redistributes the load among the other five, and the aircraft can hold its position and land. Usually, not always: it depends on which motor fails and on how much spare thrust the build has. A hexacopter flying near its maximum takeoff weight has nothing left to compensate with.

An octocopter survives one failure with margin and often a second one, which is why it is the layout chosen to fly a camera worth tens of thousands of dollars over people, water or a film set.

The practical reading: redundancy protects what the drone carries. For a camera drone that is its own camera, a quadcopter is the right trade. Once the payload costs more than the aircraft, or the drone flies where a fall would hurt someone, six or eight rotors stop being a luxury.

How many rotors do you actually need

For almost everybody reading this, four. The honest guide:

• Photos and video of trips, family or property: a quadcopter with a gimbal. Under 250 g if you want to skip FAA registration.
• Learning to fly, or a gift for a kid: a small quadcopter with prop guards, flown indoors or in an open field.
• Racing or freestyle: an FPV quadcopter with goggles.
• A mirrorless camera, agricultural or survey work, or a build project: a hexacopter.
• Cinema cameras or heavy industrial payloads: an octocopter, usually bought through a dealer and flown under Part 107.

The assistant at the top of this page turns those three questions into a filtered table.

QuadcoptersHexacoptersOctocopters