Following are the things that should be kept in mind while choosing a motor for your drones
Thrust to weight ratio:
It is the golden rule when choosing a motor for your drone. Ideally your drone should be able to hover in midair at half throttle, which means it should be able to produce 50 percent more thrust than the multirotor.
For example if the total weight of the drone frame is 800 grams than the motor should be able to exert to the force of 1.6 kilograms. But if you are focusing on photography then you could use lower thrust to weight ratio considering the fact that you will be flying gently. So it means you can add other components on your drone like extra batteries or a heavier camera.
Efficiency of the motor:
Efficiency is the ratio of thrust produced to the power used. The more efficient your motor is the longer it is likely to fly. Ideally motor which have an efficiency of 7 are considered good but if your main focus is on aerial photography then it is better to consider a motor with efficiency of 18. For more details you can visit howtodrones.com/
But if you are also considering aerobatic stunts then it’s better to consider one with a high RPM but it will reduce your efficiency. All that matters is how you want to use your drone.
Movement of motors:
The other main factor is the movement of motors. It is better to that two motors move in a clockwise direction while the other two move in an anti-clockwise direction. In this way it is easier for the user to fly the drones.
It is also possible that all the motors can be attached in the same direction clockwise or anti-clockwise but it would be rather hard to fly the object in that case.
Higher the pole count mean lower RPM and lower the pole count means higher RPM. Higher pole count requires more voltage during its flight but produces greater torque. It is better to use larger blades with these motor devices. Take a look for more information.
While on the other hand motor with lower pole count requires smaller blades and coming with smaller torque and lift-off the ground. The other advantage of higher pole count is that it eliminates the requirement of a gearbox.
KV value is also known as the RPM/volts. From the above point we can infer that the higher pole count the lower will be the Kv value. By Kv we means constant that gives us the RPM of the motor when the potential difference of 1 volt is applied to the motor.
When the Kv value decreases there is an increase in the torque produces by the motor. But for low Kv values you would need smaller propellers which guarantee greater speed but low efficiency.
Type of motor:
There are two type of motors that are used in a drone
- Disc type motor:
They are shaped in the form of a disc. They are very light and produce high torque. They have a higher pole count and lower Kv value. This leads to the necessity of large propellers, providing you with longer and stable flights with minimal turbulence and noise.
- Barrel type of motor:
They are the opposite of disc type. They come in the shape of barrel, heavier in structure and produces less torque. Having lower pole count and higher Kv value, but the flight is not as stable as the disc type.