For many professional pilots, they tend to build their own racing weapons, however how to choose the best combo between motors and propellers for your lovely quadcopter is surely the most important.
From where to start?
Motor size comes to be the first!
To begin with, you need to answer the following 2 questions:
- What’s your quadcopter’s planned total weight ?
Since you have’t start to build, when you consider the total weight, you need to involve the whole components: the frame, Flight Controller, PDB, wires, motors, battery, HD camera and gimbals, or something others. So you need to make an estimation about the total weight and also need to update the number when you have new idea about adding different components.
- What’s the size of your frame?
By knowing the size of the frame, you should know the maximum propeller size that can be used.
Motor size and KV
Brushless motors in RC is normally indicated by a 4-digit number – AABB. “AA” being the stator width, and “BB” being the stator height. Basically, the wider and taller the motor is, the more torque it can generate.
FPVMODEL MC 4014 340 KV brushless motor
KV is another important parameter, it’s the theoretical increase of motor RPM (rotation per minute) when voltage go up by 1 volt without load. For example, when powering a 2300KV motors with a 3S LiPo battery (12.6V), the motor would spin at about 28980 RPM. This is just an estimation by the way.
But once you mounted a propeller on the motor, the RPM won’t be that high due to resistance. Higher KV motors would attempt to spin the propeller faster, but lower KV motors normally generate higher torque. That’s why we tend to see larger props are paired with low KV motors, and smaller props with high KV motors.
So when choosing motor and propeller it is important to find a balance between RPM and torque.
N and P
You might sometimes see something like “12N14P”. The number before the letter N means the number of electromagnets in stator, and the number before P means the number of permanent magnets in the motor.
Most motors have the same 12N14P configuration, some lower KV motors would have more electromagnets and permanent magnets to help increase torque more efficiently (and thus more expensive). While it’s good to know what this is, it’s not an essential piece of information when picking motors.
Frame Size => Prop Size => Motor Size and KV
Most of the times by knowing frame size, we can estimate what sort of motor we should use. This is because frame size limits props size, and prop size limits motor size and KV. But anyway, always check motor thrust test data to verify the current draw does not exceed safety rating of the motor, when pairing the propellers you want to run.
Comparing between motors
Once you have decided on the size and KV of the motors, you may already have many motors to choose. To pick the best motor for your application, you should consider the following factors:
- Current Draw
- Weight – Moment of Inertia
Specification about FPVMODEL MC4014 340KV bruthless motor
Higher thrust gives you top speed, but you also need to consider efficiency.
Higher thrust gives you top speed, but you also need to look at efficiency, making sure it’s not using a ridiculous amount of power that is exceed what your hardware can support.
Your choice of motor and propeller may affect your choice of batteries too. If your quad could draw a large amount of current at full throttle, youre battery’s max discharge rate has to be able to keep up in order to provide the power, as well as they don’t overheat and go buff.
One thing that oftern get overlooked is motor weight, it is more important in racing drones. It does’t only affect the total weight of your quad and thrust to weight ratio, it also affects the moment of inertia of your quad.
When your quad is doing flips and rolls for example, it takes time to pikde up the angular acceleration and eventually move to the desired position. If your motors are heavy, it will take the quad longer to do this, and therefore feels less responsive.
Propellers generate thrust by spinning and moving air. The more air it can move, the more thrust it will generate.
Many pilots have different choice as to the material, shape, size and the number of blades requirements of propellers.
With a well balanced motor and propeller combination, your quadcopter should achieve great efficiency, not only improve battery life time, but also allows great user con,trol experience.