Multicopter is an aircraft built according to a helicopter scheme, with three or more rotors.
A Brief History of Quadrocopters and
Multicopters
Multi-rotor helicopters were developed in the
early years of helicopter construction. One of the first quadrocopters that
actually got off the ground and could stay in the air was created by Georgy
Botezat and tested in 1922. The disadvantage of these devices was a complex
transmission, which transmitted the rotation of one motor to several screws.
The invention of the tail rotor and swashplate put an end to these efforts. New
developments began in the 1950s, but things did not progress beyond prototypes.
Multicopters received a new birth in the XXI
century, already as unmanned aerial vehicles. Due to their simplicity of
construction, quadcopters are often used in amateur simulation. Multicopters
are convenient for inexpensive aerial photography and filming - a bulky camera
is removed from the range of propellers.
Operating principle
According to the principle of control,
multicopters are:
* Autonomous
* Remote controlled (unmanned)
Multicopters have 3 or more constant pitch
propellers (there is no swashplate, unlike single and twin propellers). Each
propeller is driven by its own motor. Half of the propellers rotate clockwise,
half counterclockwise, so the multicopter does not need a tail rotor.
Multicopters are maneuvered by changing the rotational speed of the propellers.
For example:
accelerate all screws - lifting;
speed up the screws on one side and slow down
on the other - movement to the side;
accelerate the clockwise rotating screws and
slow the counter-rotating in the plane.
The microprocessor system translates radio
control commands into engine commands. To ensure stable hovering, multicopters
are obligatory equipped with three gyroscopes that fix the aircraft's roll. As
an auxiliary tool, sometimes, an accelerometer is also used, the data from
which allows the processor to establish an absolutely horizontal position, and
a pressure sensor, which allows the device to be fixed at the desired height.
Also, sonar is used for automatic landing and keeping a low altitude, as well
as for flying around obstacles. The use of a GPS receiver will make it possible
to record the flight route in advance from a computer, as well as return the
aircraft to the take-off point, in case of loss of the control radio signal, or
take the flight parameters promptly or later.
There are also three- and five-rotor
helicopters (tri- and pentacopters). One of the motors there is located on a
movable platform strung on an axis, the angle of rotation of which is changed
by a servo drive - this is how the apparatus rotates around its axis.
Separately, it is worth noting the experimental devices: bicopters, quadcopters
with variable pitch propellers, quadcopters with impeller motors, but they did
not receive any distribution.
According to the options for placing the screws
in relation to the axis of motion and depending on their direction of rotation,
several types of multicopters are distinguished:
Modern use of multicopters
The modern application of multicopters is very
diverse: from toys, delivery of goods, amateur means for photography and video
filming to passenger and cargo vehicles and combat robots.
Amateur and professional multicopters use
brushed and brushless electric motors and lithium polymer batteries as a power
source. The screws can be installed directly on the motor shaft or through a
gearbox.
This imposes certain restrictions on their
flight characteristics: the typical mass of a multicopter is from 1 to 4 kg,
with a flight time of 10 to 30 minutes (30-50 minutes for unique single
copies). The lifted payload by models of medium-sized multicopters and carrying
capacity is from 500 g to 2-3 kg, which allows lifting a small photo or video
camera into the air (usually an action camera in cheaper models, or SLR cameras
in professional ones). There are also quite large models of multicopters, with
the number of rotors on the order of 6-8 (hexa and octocopters), capable of
lifting a load weighing up to 20-30 kg into the air. To increase the carrying
capacity, the coaxial arrangement of the bearing rotors is used, which in the
case of a hexacopter, for example, gives 12 motors and 12 propellers, arranged
in pairs on 6 bearing beams. The flight speed of a multicopter can be from zero
(stationary hovering at a point) to 100-110 km / h. The battery power reserve
allows individual multicopter models to fly up to 7-12 km, in practice, the
range (the maximum distance they are able to fly away and then return to the
take-off point) is usually limited by line of sight (100-200 m with manual
control) or range of radio control equipment and video link. At the same time,
the best examples of such equipment, using radio signal power amplifiers and a
system of directional antennas, are capable of providing stable radio control
and video links at distances of up to 100 km. Thus, it is the flight time that
imposes the greatest limitation on the range of multicopters.
These limitations lead to the fact that multicopters are usually used as "short-range" devices: for amateur flights close to oneself, for photo-video filming of close objects, and so on. For comparison, unmanned aircraft with a battery of the same capacity can fly 10-15 km at a flight altitude of 1-2 km.