How to choose Motor and Propeller for Quadcopter and Multicopter

motor propeller

You won’t believe how much maths and aerodynamics are involved when the engineers are designing the propellers and motors. Therefore you know how difficult it is to choose the best motor and propeller combination for your quadcopter for best performance.

Fortunately this is not a new subject, and there are so many people shared their experience about this. Also there are some general rules you can follow to choose the optimal and effective motor and propeller combination.

As part of the quadcopter tutorial I will share some information for beginners about how to choose motor and propeller for quadcopter, which also applies to other types of multicopter.

Here is a guide about the types prop adapters for your motors, and the pros and cons you might be interested.

Some basic concepts when selecting Motors

brushless_motor_1

When selecting motors, there usually are specification that comes with the motor either provided by the seller or manufacturer. You should be able to find information about the power, thrust, rpm etc. This is an example of the 18-11 2000kv Micro Brushless Outrunner (10g) on Hobbyking.com. Google it if you are not sure what each name represents in the data sheet, they are really basic and I am not going to go over them here.

quadcopter motor data-sheet

quadcopter motor spec

To choose a motor we first need to how much weight you are planning to take, and then to work out the thrust required to lift the quadcopter. A general rule is that you should be able to provide twice as much thrust than the weight of the quad. If the thrust provided by the motors are too little, the quad will not respond well to your control, even has difficulties to take off. But if the thrust is too much, the quadcopter might become too agile and hard to control.

A rule of thumb is Required Thrust per motor = ( Weight x 2 ) / 4

For example if we have a quadcopter witch the flying weight might be around 1 KG. Using the equation above, we now know we’re looking for a total thrust of 2 KG and 500g per motor. Of course you will have to guess the final weight of your quadcopter, when estimating, don’t forget to add the weight of the motors and propellers which vary. If you are thinking about FPV or aerophotography, you will need to add the weight of the camera as well.

Although you can choose the motors for the weight you want to carry, it’s always a good idea to carry as little weight as possible. Lightness is very important to all aircraft because any excess weight could reduce your battery life and maneuverability.

More tips on Motor Efficiency

A multicopter is more efficient when it’s lighter, so you need to pick a good battery that has good capacity but light weight. This post shows you how to find the perfect balance when choosing LiPo batteries for your multicopter.

Battery and weight is not the only factor we need to consider when it comes to Efficiency, there is also motor efficiency. When choosing motors, apart from motor KV and thrust, we also need to look at Watt’s and efficiency.

It’s like cycling, cycle at lower gear enable you to cycle faster but it’s harder to peddle. If you are going uphill, and it’s getting steeper, you will eventually come to a point where peddling becomes too heavy and you are getting slower although you are peddling very hard. This is where you lose efficiency.

The same applies to brushless motor, the higher efficiency the better. A 70% efficient motor produces 70% power and 30% heat. A 90% efficient motor produces 90% power and 10% heat.

With less efficient motors not only are you wasting a lot of power (thus flight time), you also get smaller thrust on full throttle. Most important, because the motor runs so inefficient, the response time suffers. It will take the motors more time to change rpm and this will influence the stability of your quad, and the copter will be less stable.

After you received your motors, the first thing you should do is to balance it. Although it’s not always necessary, it’s good practice.

Some basic concepts when selecting Propellers

images

A quadcopter uses two clockwise(CW) and two counter-clockwise(CCW) propellers. Propellers are classified by length and pitch. For example 9×4.7 propellers are 9 inch long and has a pitch of 4.7.

Generally, increased propeller pitch and length will draw more current. Also the pitch can be defined as the travel distance of one single prop rotation. In a nutshell, higher pitch means slower rotation, but will increase your vehicle speed which also use more power.

 

propeller-pitch

When deciding on length and pitch, you need to find a good balance. Generally a prop with low pitch numbers can generate more torque. The motors don’t need to work as hard so it pulls less current with this type of prop. If you want to do acrobatics, you will need torque propellers which provide more acceleration and it puts less pressure on the power system. Lower pitch propellers will also improve stability.

A higher pitch propeller moves greater amount of air, which could create turbulence and cause the aircraft to wobble during hovering. If you notice this with your quadcopter, try to choosing a lower pitched propeller.

When it comes to the length, propeller efficiency is closely related to the contact area of a prop with air, so a small increase in prop length will increase the propeller efficiency. (pretty much like swimmers with larger hands and feet can swim faster, but also more tiring for them)

A smaller prop is easier to stop or speed up while a larger prop takes longer to change speeds (inertia of movement). Smaller prop also means it draws less current, that is why hexacoptors and octocopters tend to use smaller props than quadcopter of similar size.

For larger quadcopters that carry payloads, large propellers and low-kv motors tend to work better. These have more rotational momentum, and will more easily maintain your aircraft’s stability.

There are a few different types of propellers, such as plastic, carbon fibre etc, check out this post for more info.

Some tips on how to choose Motor and Propeller

There are two ways I usually do.

  • Observe and Research – go on to youtube and search people’s flying video, not only you can see the result of their quadcopters, you can also check out their setup, what motor and propeller they are using. It’s essential to learn from people’s experience because it’s free :-)
  • Understand the maths and Experiment – if you have a great mathematical mind and have spare budget, and could not find any information about the motor and propeller combination you want to use, you could experiment with different setups! Although it requires more money and more time.

Even the for props of the same size and pitch, when they are made of different material and by different manufacturers, the performance also tend to be very different. Here is an example where I compare the 5030 props of two different brands.

Conclusion

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 control experience. Hope this post has helped you select the best motor and propellers, and don’t hesitate to share your ideas or questions with us.:-)

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68 thoughts on “How to choose Motor and Propeller for Quadcopter and Multicopter

  1. Hi, i want to know the real price of Hexacopter Motors with different manufactres, i hope i would see my reply through my email. And i haved prepared everything such as frame, Camera, and Controller but Motors and ESC we don’t have it in our area. i hope you guys you can help me where to get six (6) Motors and six (6) ESC for my new project “Hexacopter”.

    Do you guys export it if i buy it from your company? am in Nigeria – Leaving in Borno State. how many days will take you to bring it back wen i purchase it.

  2. Hey nice article above.
    I am a first year college student.My friends and I are planning to make a very basic quadcopter. We are having problems regarding specifications of motor and battery. It would be very nice if you could help us out. Our quadcopter should be around 1100 grams(1.1kg). We are planning to use wood for frame. It would be very helpful if you could tell what kind of motor should we use and how powerful battery should be sufficient. We plan to use 4 motors and 1 battery only.

  3. Hello bro,
    I am making a quadcopter using the following parts
    1)hextronik nanowii V01 from HK site
    2)multistar motor type 2213 935KV
    3)10*45 propeller
    4)3 cell 3000mAh tunigy battery
    5)turnigy plush 30Amps*2 for two motors and 25Amps*2 for the other motors
    6)Flysky controller model FS-CT6B.

    So far I have fully assembled my quad all the motor direction and all connections are correct.I used multiwii to program my nanowii controller,so i have set as #define MINTHROTTLE 1150 and #define MAXTHROTTLE 2000 also i calibrated my ESC initially using the #define ESC_CALIB_CANNOT_FLY command in the config.h of the multiwii.ino,but I am facing a problem.
    After I arm the motors and star to raise my throttler one of my motors(rear-right) is staying constant at 1150 for a while while the other three motors raise up.After sometime the fourth motor(rear-right) also increase and at full throttle three motors are running at 1960rpm while the fourth motor(rear right motor) runs at 1660rpm(as seen from the multiwii GUI). Even during the flight it has terrible problems during take off in fact it is not taking off since three motors are at a higher throttle it tumbles over rapidly. Please Help..

    • Hi Bro, First of all, why are you running 2 different types of ESCs?
      you need four identical ESCs, Then calibrate your ESCs and try again.
      thanks
      Oscar

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