Part 1： Things to consider when choosing drone motors
1. Weight of your drone
The very first criterion for selection of right motor for your drone is to have clear idea about overall weight of drone itself.
You can have approximate weight idea for your drone by simply calculating weight of its individual parts or components. But note that the list must include all parts like payload (if you are connecting gimbals and camera), battery unit, motors, wires, PDB, flight controller and frame of the device.
Once you know the overall size of frame then it can help you to determine right propeller size. Whereas the idea about size and weight of propeller will help users to know about the overall thrust of motor that they will need for perfect lifting of drone during flights. Your decision will help to maintain speed of drone in air and this weight will also contribute in flight time adjustments.
2. Thrust to weight ratio
Do you know the golden rule for selection of drone motor? It must allow your drone to hover in the midair with half throttle. It clearly means that your selected motor must be capable enough to produce about 50 percent higher thrust as compared to multi rotor.
This is a very essential parameter as it means your motor is going to have additional thrust to keep your drone safe during windy weather or at the time of flight maneuvers.
Let us consider a situation: suppose your drone have overall weight of 650 grams then we need to pick a motor that can generate at least twice amount of thrust. Means thrust must range somewhere around 1360 Grams where each motor must be capable enough to produce 340 grams thrust.
And in case if they are able to produce higher thrust then this rated value, your drone will naturally become able to move with much faster speed.
The formula used for calculation of motor efficiency is “thrust/power used in W”; its overall unit becomes g/W. now, if you have higher value of g/W rating that means your motor is more efficient and it will assist drone in longer flights.
Professionals recommend choosing a motor that has efficiency value near about 7 or above this. There are chances that a motor could be efficient with its lower throttle range; in that case they will lose efficiency with increasing current range at higher limits.
When you connect motors having low efficiency to your drone unit then you have to make lots of compromise for flight time as well as energy. It will also cause voltage sags for your batteries. Never forget to check thrust/current ratio while buying new motor for your drone.
The torque range helps to define the ability of motor to shift between RPM values. This change ultimately decides responsiveness of drone in air. If your motor has high torque value then it will naturally lead to snappy response as RPM will accept faster changes. It will also lead to lesser propeller wash.
If you have high torque value for your motor then it means it is capable enough to run much heavier props but will also suck more current. In case if you try to fir a heavier propeller on low torque type motor, it will not be able to achieve the desired RPM value or will not be able to generate enough torque for spinning.
Ultimately, it will end up making lower thrust while drawing lower current from system. However, there is one disadvantage of connection high torque type motors; that is, it generates more oscillations and they cannot be tuned so easily.
Note that, high torque type motors are able to generate faster response rate so users can move between different RPM rating easily and efficiently. It may also amplify error and can cause oscillations even at yaw axis.
5. Pole Count
Next important consideration is motor pole count. You will generally find two options for this: first one if quadcopter motors that have higher pole count. These types of motors are able to produce greater torque value but at the same time it will demand more voltage for operation.
Note that these motors are able to produce lower RPM. Professionals suggest choosing larger blades for such motors.
If we talk about the second category, here you will find motors having lower pole count but they deliver higher RPM. Now, these motors will be accompanied by smaller blades and will serve with smaller lift from ground.
If you want to get rid of additional gear box then it is essential to start with higher pole count.
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Part 2: Types of motors:
Brushed DC motor
Brushed DC motors possess a rotating armature that works like a electromagnet having two poles. A rotary switch is connected that helps to reverse current direction for every half cycle so that poles can be pushed or pulled against permanent magnets connected outside motor.
It is commonly used as a power tool for drones.
It can serve users up to 1000 hours or less.
In case of Brushed motor designs, you need to invest upon continuous maintenance for carbon crushes to ensure proper energy consumption and satisfactory operation.
Brushless DC motor
Brushless DC Motors do not possess brushes, they just have a permanent magnet and it switched with electronic polarity changes. Its movements can be controlled via a dedicated electronic controller and speed feedback mechanism.
These motors are commonly used for drones that demand higher rotation speeds to manage flights.
Brushed DC motors are capable enough to work effectively up to more than 1000 hours
Brusheless motors are highly energy efficient as compared to brushed ones.
If you are working on a project where motor is expected to be used for very less time, it is recommended to connect brushed DC motor as it will provide sufficient output with cost effectiveness. But in case if you need motors continuously or when your device is going to work on higher power rating then brushless motor will be best idea for long hour flights.