Types of Multirotor
As I write this, I am embarking on building my second multirotor. When I first started learning about multirotors, I, like many beginner multirotor pilots, focused on quadcopters, which is just one of many types of multirotor. I built my very own SK450 Dead Cat quadcopter, and I have been having tons of fun flying it. You can learn more about that particular project by reading through the tutorial I wrote on Instructables.
Anyway, now I am working on a Y6 copter, the details of which I will be writing about in the coming weeks, but before all that, I wanted to write a more general post discussing the different types of multirotors. There are a bunch of them, so let’s dive in.
Types of Multirotor
Tricopters have three motors. They are typically arranged in a Y or sometimes a T shape. The front two motors are mounted in fixed positions, like the motors on all other multirotors. The motor in the rear is what makes tricopters unique. The rear motor can be tilted laterally using a servo. This servo mechanism provides yaw control for the craft.
Tricopters are the least expensive type of multirotor because they have the fewest motors. They do also require a servo, but servos are generally much less expensive than brushless motors. Another benefit is that tricopters have the widest angle(120 degrees) between the front two motors, making it easy to do aerial videography while the propellers stay out of shot.
The servo assembly on tricopters can easily be damaged in a crash. Plus, because it has the fewest motors among multirotor aircraft, it also has the least lifting power.
Quadcopters have four motors. Quadcopters are the most popular multirotor design because they strike a balance among mechanical simplicity, lifting capacity, stability, and ease of control.
The four motors on quadcopters are arranged such that each motor spins in the opposite direction than its neighbors. Two of the motors spin clockwise, and two counterclockwise. This arrangement creates a balance of rotational forces, meaning that the quadcopter will not yaw. For more information about how quadcopters work, please read The Physics of Quadcopter Flight.
There are many different quadcopter designs:
The quadcopter X configuration is the most popular quadcopter design, making it the most popular multirotor design overall. The X configuration is commonly used for aerial photography/videography because the camera can point out between the front two motors.
The + configuration is commonly used in acrobatic flying because, compared to the X configuration, a + configuration quadcopter flies more like an airplane and is easier to control.
A Y4 quadcopter looks like a tricopter, but instead of a servo motor on the rear motor, Y4 copters have a second brushless motor mounted underneath the first. This way, yaw control is achieved by altering the relative speed of the two rear motors. While Y4 copters fly the same as tricopters, they have more lifting power and are more robust due to the lack of a servo mechanism.
The Vtail is a quadcopter with the front two motors on normal quadcopter arms, while the rear two motors located in close proximity, tilted at an vertical angle. A V-Tail is similar to a Y4. This is not a very popular design because it is quite a bit less efficient than the other quadcopter designs.
Pentacopters have five motors. You will not find much information about pentacopters out there because this is the least popular multirotor design. One advantage of pentacopters is the wide angle of the front arms, making it easy to shoot aerial photos and videos without the props making it into frame. Plus, pentacopters have more lifting power than tricopters or quadcopters. There are a few examples of pentacopters around the web, including one on Robot Kingdom.
Hexacopters have six motors. Like quadcopters, the motors on hexacopters are arranged in pairs with one turning counterclockwise and one turning clockwise. In other words, hexacopters have three counterclockwise-spinning rotors and three clockwise-spinning rotors. Hexacopters and quadcopters have similar flight mechanics but hexacopters have more lifting power because of the extra two motors. This is beneficial to pilots who wish to carry camera equipment more sophisticated than an average action camera, like high-end DSLRs.
One other interesting advantage of hexacopters over other multirotor designs is that unlike multirotors with fewer motors, with a sufficiently sophisticated flight controller, hexacopters can stay in the air despite one of their motors failing. The downside is that hexacopters are larger, heavier, and more expensive than other multirotors.
There are three different types of hexacopter:
X Configuration/+ Configuration
Like quadcopters, hexacopters can be configured as X or + mode. In both of these designs, the rotors are arranged with equal spacing around the body. In + mode one of the motors faces front, and in X mode, two of the motors face front. Like quadcopters, X mode is most commonly used for aerial photography/videography and + mode is most commonly used for acrobatic flying.
Y6 copters are similar to tricopters, but they have two motors per arm, mounted one on top of another. The pairs of motors spin in opposite directions creating a balance of forces and preventing unintended yaw.
Y6 copters are more compact than other hexacopters but they are also slightly less efficient.
Octocopters have eight motors. Although it is certainly possible to build a multirotor with more than eight rotors, there is a point of diminishing returns where, unless you are planning to transport concrete blocks with your multirotor, the extra lifting power is just not worth the added cost and complexity. Octocopters are very similar to hexacopters, like hexacopters are similar to quadcopters, but octocopters obviously have more lifting power than hexacopters. Also like hexacopters, octocopters can be build in three different configurations.
X Configuration/+ Configuration
Like hexacopters, octocopters can be configured as X or + mode. In both of these designs, the rotors are arranged with equal spacing around the body. In + mode one of the motors faces front, and in X mode, two of the motors face front. Like quadcopters, X mode is most commonly used for aerial photography/videography and + mode is most commonly used for acrobatic flying.
X8 copters are similar to quadcopters, but X8 copters have two motors per arm, mounted one on top of the other. In this way, X8 copters are also similar to Y6 copters. X8 copters have much more lifting power than quadcopters because they have twice as many motors. But, the overall efficiency of the system is less than the efficiency of a quadcopter.