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Motors help in providing the power for our multirotor to transcend the sky. It is basically the impetus, power, or energy behind those drones having maximum influence on the flight characteristics of every multicoptor. Here a minute change in the design configuration corresponds to very notable impact on the responsiveness of a multicoptor.
Most of the motors for multirotor are labelled as brushless motors, and work by using three phase power to drive electromagnets that spin the motor. Now what is electromagnetism?? It plays a pivotal role in functioning of both brushed and brushless DC motors as it helps in converting electrical energy to kinetic energy. The combination of attraction and repulsion of the electromagnet or permanent magnets translates into rotational motion of the motor shaft.
Image credits : GalcoTV
The major principle behind brushless and brushed motors bear a close resemblance. When an electric current is passed through the windings of the motor, magnets distributed within the motor are either attracted or they are repelled. This iterative fashion of repetitive repulsion and attraction of the magnets eventually translates into a revolution of the shaft. This allows the motor to spin an attached propeller at high speeds which helps in producing shaft.
Image credits : GalcoTV
While discussing the functioning of brushed motor, one must understand that the permanent magnetic field that surrounds the rotor is provided by the stator.
Image credits : Drone Omega
The rotor of this brushed motor is an electromagnet which is greatly influenced by the surrounding stator. There are two brushes attached to DC power and they contact the commutator ring at the base of the rotor. The commutator ring is divided, therefore its rotation will periodically reverse the direction of the current flowing through the rotor, as its rotation causes the commutator to reverse its polarity. The alternation of the commutator ring polarity translates into continuous revolution of the rotor. This entire process occurs inside a motor can, which provides extends excellent protection for all the intricate components. Although, efficiency of the system is compromised because of the greater thermal insulation of the internal mechanics. It is possible to reverse the rotation direction of the motor by inverting the polarity of the DC power input. Due to the contact of the brushes with the commutator, longevity of the brushed motor is greatly reduced in comparison to the brushless motor. A micro class multicpoters prefer a brushed motor because of their small size, lighter weight and simple driving technique which eventually helps in improving their compatibility.
Image credits : Insight Solutions Global
As clearly evident from the name, brushless FPV drones don’t have brushes. They have two primary components, the rotor and the stator.
Image credits : Nidec Corporation
The rotor is mounted on the central unit, stator. The stator comprises a network of radial electromagnets that alternatively switch from power on and off states to produce a temporary magnetic field when a current is passed through the windings. Whereas the rotor is a collection of permanent magnets which is carefully positioned in close proximity to the semi-permanent electromagnets of the stator. Attractive and repulsive interaction of the stator and rotor magnets is converted into rotational movement. During assembly, the shaft of the rotor is inserted into a pair of ball bearings located in the stator that maintain linear, smooth revolution of the rotor.
The brushless motor can’t be driven directly. It is powered by DC current. The brushless motor is wired to the control electronics, that helps in eliminating the need for brushes or a commutator, effectively. Longevity of the brushless motor is excellent as there is an absence of any physical contact between the rotor and the stator. The efficiency of brushless motor is much more than brushed motor. The brushless motor finds extensive application in mini and some micro multicopter, where high power outputs and efficiency are highly prioritized.
One can figure out the dimension of a brushless motor by a four digit code that highlights which gives in the dimensions of the stator in millimeters where the first two numbers in the series determine the diameter of the stator and the final two mentions the height of the stator. On the other hand, the size of a brushed motor can be identified through a simpler two number convention that evidently describe the diameter and height of the exterior can in millimeters.
Mounting patterns and thread sizing is determined by the variant of motor and what it’s primary application is. The mounting pattern usually describes the positioning of the threaded bolt holes on the base of the motor. Each number describes the diameter of a circle. Usually, four holes are placed along the circumference of the circle, if two numbers are given, two holes are placed on each circle.
Image credits : GetFPV
220X – 240X: A 16x19mm mounting pattern is often seen in use, however, 16×16 is becoming increasingly common these days. The threaded holes are M3. The threaded shaft diameter is M5.
180X: A 16×12 mounting pattern, threaded holes are M2 and M5 threaded shaft diameter is typical.
130X – 140X: 12×12, the threaded holes are M2 and a M5 threaded shaft is typical.
110X: Often 9×9, threaded holes are typically measured as M2. The shaft is not threaded and it usually measures 1.5mm in diameter.
Image credits : GetFPV
The velocity constant (kV) is usually determined by the number of rotations of a motor within a time period of one minute without a load (no propeller) and at a constant current of 1 Volt. kV is a representation of how fast the motor can spin, potentially.
While choosing a motor, one clearly goes by the thrust as it has a primary role to play. The output in form of thrust of any motor is usually measured in grams and varies extensively depending on how fast the motor can spin and the propeller that it is rotates.
|Frame Size||Prop Size||Motor Size||KV|
|150mm or smaller||3″ or smaller||1105 -1306 or smaller||3000KV and higher|
|180mm||4″||1806, 2204||2600KV – 3000KV|
|450mm||8″, 9″, 10″ or larger||26XX and larger||1200KV and lower|
When it comes to the response time of a motor, one uses the yardstick of torque in order to measure it, as it determines how quickly a motor can reach a certain specified RPM. The amount of torque a motor can produce as its output favors the selection of a specific propeller. A greater torque is usually achieved from a larger stator, but again, it will eventually add to the extra weight of the motor and hinder flight experience. Hence, one must strike for an appropriate balance.
Well, in order to achieve the required efficiency, one must maintain a proper equilibrium between the entering electrical power supply and the mechanical power harnessed by the rotating/spinning motor. If one goes on to prioritize a certain attribute over the other, one has to compromise on the other. A combination of high speed and short flight times are usually seen in a combination.
That was our take on the powerhouse of FPV drones. Don’t let your thirst for digging deeper and flying higher reach a dead-end here. Keep exploring because the sky shall be your limit.
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If a motor takes longer time to reach certain RPM will it be effective for slow motion elevation recording? Same goes for descent.