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.

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 = ( 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

Motor KV and thrust are NOT the only factors we need to consider when purchasing motors. Watt’s and efficiency are equally important.

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.

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.

Finally, there are some great quadcopter calculators on the internet that are designed specifically for multicopters. They might help you find the component combinations to maximize your quadcopter performance.

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

  1. I want to make a quad copter for HD video recording . so total weight is around 3.5 or 4 kg so i required parameter of motor , propeller size and battery required on it.

    • that’s heavy
      you are looking at motors that can produce more than 2KG of thrust each, that is going to be expensive.
      I have never built anything this big before so I can’t give you any useful advice.

    • Let’s have a look.
      What is the total weight of your quad when take off, and what is the spec of your motors? (thrust at battery voltage 3.7V per cell, and current draw at that thrust). Size of your battery? (C-rating, capacity and weight)

  2. i have read a book about quads and for blade aerodynamics and trust calculating i need some data about the propellers blade airfoil like drag and lift and some angles.
    how can i find these things?i need a datasheet.how can i find it?

    • you don’t need a university degree to build a quad, forget about “aerodynamics”. Follow what I mentioned in the post and you should be fine. usually thrust data are provided on the product page on the websites, given the size of the prop.

    • Total weight of your quad?
      Max Thrust of your motors for the battery you are using?
      Current draw of your motors?
      C rating of your battery?

  3. hi sir ,im planning to make a quad the estimated weight with components in 950g-1kg
    i planning to use 30A esc, 980 kv motor, 3300mAh battery 25c/50c(burst) which propellor to choose for this configuration sir ( weight of battery 247g)

    • HI!
      I would suggest to try 9 inch and 10 inch propellers, see which is better.
      9 inch should give you better stability, but 10 inch will give you longer flight time.

  4. Thanks for ur valuable comment sir, i would also like to know what will be the flying time with 10×4.5 prop and above said configuration sir.
    And Sir as soon the buzzer of the low voltage alarm starts we need to land the quad sir?

  5. Hi,

    Usually I order from hobbyking, but I can’t find at the thrust data in the data sheet of the motors.
    How can I calculate the thrust of the motors? If it possible of course.
    What would you recommend (motor and prop) for 2kg weights fpv flying?

    My quadcopter: SK450 with “landing gear”, KK2, turngy plush 30A, NTM Prop Drive Series 28-26A 1200kv / 286w, 1045 prop.

    First I tried to fly this config with 845 prop, but it could not take off, then I changed to 1045. It lfew for a while but I recognized the motors where to hot, and the battery also, so I stopped. I knew this config won’t enough strong for that flying but I had to try it.

    Thank you in advance!
    Regards,
    Imi

    • HI,
      there is no way you can calculate the thrust of a motor accurately, unless it’s provided by the manufacturer, or measured by yourself.
      have you checked the “file” tab in the product page on Hobbyking? sometimes there is a datasheet file in there, or data from some users.
      If no, try google it, I am sure someone has measured this and share on the internet.

      NTM Prop Drive Series 28-26A – This motor seems to run best with 1060 props, each motor can generate 967g thrust for 19A at 100% throttle, so this motor should be good enough for 2KG quad.

      However, also make sure your battery’s C rating is high enough.
      Good luck!

  6. Hi,
    I want to make a quad for lifting about 1 kg.and so i required parameter of motor , propeller size and battery required on it.(min flight time is 10 min).
    Thank you very much.

  7. Hello, I have a beginner’s question.
    Generally speaking which type of motor will draw more power,
    The Low Kv or the High Kv motor?

    I’m building a quad and I want to get a few more minutes of flying time and I don’t know if I should use a 1000 kv motor or something around 700kv, I know I’ll be using different size propr obviously but which motor requires more power to spin?

    • Hi, If it’s the same model motor, the higher KV motor will draw more current with the same voltage and prop. For example, the Cobra 2204 2300KV will draw more current (higher power) than the Cobra 2204 1960KV at 3S battery.

  8. Dear,
    I want to make an airplane of weighted about 1.5 kg including all access.
    An esc of 30 amp . A battery of max 2200 mah . 9g micro servo. So which motor you would refer me.
    In runner or out runner , of which rpm and efficency and thrust and propeller size.
    Tell me about that model which is easily available in pakistan and best for me.
    Thankful to you.

  9. Hi!

    I am a 12 year old and have built a small 330 size quad. I am slightly worried about my motors not being powerful enough for the quad. My quad specs are 1.1kg, D2822 Turigy Aerodrive 1100kv Motors (which have a thrust amount of 540g per motor) and a 2200mah, 3s 40c lipo battery. Am I straining my motors? Oddly, the battery, ESCs and motors are barely warm at all after flight. I also carry a gopro and the motors and other parts are fine. I look a the dji phantom which is much lighter and it has 935kv motors… Am I missing something? The quadcopter is also still quite maneuverable has normal flight characteristics as my others. Just want to make sure I don’t damage my quad!

    P.S. I am running 8*4.5in props for lifting more!

    Thanks!

    • Update: the weight is actually 1.2 kg and the motors are also quite warm now after flight and with a go pro, I take off at 1/2 throttle (a bit more in fact). Without a go pro, I take off at less than 1/2 throttle.

      • Hi Tristan,

        it’s great to see young minds like you picking up this hobby. But I am concerned about your safety since you are only 12! Are you being supervised by an adult when doing this project?
        Quadcopter is not a toy, it can be very dangerous!

        what you have is flyable. But I would use stronger motors, because 330 size quad should be very agile being able to do arobatics, you probably want to have 1:3 weight to thrust ratio, that means having 3KG of thrust in total, 750g thrust per motor would have been better.

        But I think 1.2KG for a 330 size quad, is a bit heavy. I think normally that size should be around 700 to 800 grams (including gopro).
        try to reduce the weight down, and use your current motor should be fine.

  10. Thank you very much!! I will look into better motors and/or reducing weight.

    P.S- I am also being supervised by a parent! Thanks for your concern though.

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