Home Quadcopter Diy How to choose most efficient quadcopter motor

How to choose most efficient quadcopter motor

14 min read

No other part of the drone is as important as the quality of the chosen motor, how to choose most efficient quadcopter motor? This article will tell you how and why!

A Quadcopter as the name suggests is a multi-rotor helicopter which is propelled and lifted by four rotors. The quadcopter is classified as a rotorcraft which is opposed to a fixed wing aircraft since the lift is created by a set of propellers which are oriented vertically or rotors.

CCW and CW of motor

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The quadcopter consists of two pairs of propellers which are fixed – two of them work anti-clockwise or CCW while the other two work clockwise or CW. The control of the quadcopter is achieved with the speed variation of each rotor. The change in speed of each rotor helps in generating the required total thrust and in the creation of the desired turning force or torque.

Moter dynamics theory

The flight dynamics of the quadcopter is such that each rotor is producing a torque and a thrust around its rotation center and simultaneously creating a drag force which is exactly in the opposite direction of the flight of the aircraft.

Moter dynamics theory

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A quadcopter, like other multi-rotors, employs a configuration of a coaxial rotor for allowing more stability and power. Each of the arms has a couple of motors which move in opposite directions with one motor facing downwards while the other faces upwards.

The aerodynamics for all quadcopters is subject to the usual aerodynamics for rotorcrafts also include the vortex ring state. To allow for simple control mechanism and optimum performance, the propellers and motors need to be equidistantly placed.

Importance of most efficient quadcopter motor

Thus due to the work of maneuverability of the quadcopter depends upon the motors; you have to be very particular in choosing the motor for your quadcopter. Per chance you were to choose the wrong motor, your quadcopter will never leave the ground as without the perfect motor nothing will ever work as it should.

The most efficient quadcopter motor has a colossal impact on the performance of the drone. No other part of the drone is as important as the quality of the chosen motor. Another important criterion is the price which the motor commands since the motors are more costly if they are brushless.

How to choose most efficient quadcopter motor

How to choose motor for quadcopter? The best choice of the most efficient quadcopter motor would be one that can run anti-clockwise as well as clockwise. The drone works on four motors, a couple of which run anti-clockwise while the other two run clockwise to provide the most stable performance for the drone.

This may suggest that you should but motors that run either anti-clockwise or clockwise, but in reality, such an act would make the drone very hard to get in the air. There are systems which would help you to monitor the instability arising from this action, but then it would be very difficult to fly this drone in the manual mode if you were a novice at the game.

How to choose most efficient quadcopter motor

Moter poles

The poles which a motor possesses needs to be understood much hair splitting need not be done over this aspect as the electronics takes care of this. You need to know that more voltage is required for a motor which has a higher count of poles.

This motor produces more lift or torque; such a motor will have lower revolutions per minute or rpm. You might have to attach with these motors a larger size of blades. Conversely, a lower pole motor will require less voltage and will produce more rpm with a lower corresponding lifting power or torque. Such a motor will have to have small blades because the motor will not be able to control propeller blades of larger size.

The use of a motor with a high pole count or out-runners by the quadcopter is done so as to avoid the use of a gearbox. The motor with a high pole count has a high torque output which does mitigate the use of a gearbox for increasing the torque.

RPM and KV value of motor

The rpm/volt or the KV value is a critical aspect which you need to consider quite closely. This is so because when you consider a motor with more poles the rpm/volt or the Kv value decreases. The difference between kV and Kv is not the kilo volt as per Kv but the difference when 1V is employed when there is no load as is Kv. This Kv value therefore is a very important aspect while you calculate what a load the motor should be carrying.

RPM and KV value of motor

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For example, a 1000 Kv motor will rotate at a 1000 rpm speed at the time 1 volt is applied when there is no load. If there is a motor of 12V, then the rotating speed would be 12,000 rpm with a zero load.

In another case, a motor with 1000Kv has a rating of 120 watts and a maximum of 20,000 rpm. The maximum amount of voltage this motor will take will be (20000/1000) 20V. Similarly, the calculation for the amperes will be (120/20) 6amps.

Similarly, a motor with 4000 Kv has a rating of 120 watts and a 40,000 rpm. The voltage you will be able to apply will be to a maximum of (40000/4000) 10V and the current which the motor can maximum draw is (120/10)12 amps.

The importance of the Kv value is due to the fact that any decrease in the value of Kv there is an increase in the production of torque by the motor. This increase in the torque results in more power to lift and a higher acceleration. On the converse side, a higher Kv motor will have the capacity of production of less amount of lifting power or torque.

Propellers and Motors

You may have to choose propellers with the smaller size for a higher Kv motor. Though drones with a small size of propellers will be able to attain higher speed, the efficiency of the drone will be reduced. Conversely, lower Kv value motors will be able to have propellers with a large size thus enabling you to use a less amount of current or to lift more weight. These drones will command more stability but will possess less speed.

The bottom line is that a motor with a count of higher poles will possess a lower value of Kv but will have a less rpm at the same time will produce more power. More power will mean higher acceleration and more lift and also a larger set of propellers. While a motor with a lower count of poles will have more rpm and less output of power and a higher value of Kv. Hence, drones with smaller propellers will have less acceleration and less torque but will command a higher speed.

You may have to conduct a lot of tests regarding the best Kv rating you should have for your motor and then decide to buy it.

The lifting capacity of motors

The other criterion of choosing most efficient quadcopter motor you will have to consider is the weight to power ratio when you decide which motor to buy. A weight to power ratio of just one will be able to lift just its own weight and not be useful to lift anything else. But a weight to power ratio of say 3 will be able to lift three times its weight. The consensus will be to want a motor which is light in weight but its lifting power is very high.

Hence, it is advisable to first determine the capacity for the lifting of your quadcopter before you choose to buy a motor for it. It should be worthwhile if the payload and the drone should hover at half the capacity of the throttle when you opt to buy the motor.

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