How to choose the right motor for your multicopter drone

motor

#1

This small guide is to help you choose the right motor for your quadcopter or other multirotor. To help you with this decision, it would be desirable to have several test statistics at your disposal which can be found in the thrust data tables. Luckily, reputable manufacturers will have carried out these necessary tests so you don’t have to and these will provide you with the needed information. An example of one such thrust data table for a MT1806 is given below:

If you are totally unfamiliar with brush-less motors, its a good idea to quickly read our beginners guide to brushless motors

Where to start?

Knowing the weight of your multiorotor is the first thing we need to know. When you are building, or planning your next drone build knowing the exact weight can be difficult. However you will need to start somewhere and as choose and change components you can slowly refine the weight estimation.

I like to start by first knowing what frame I am going to use, as that gives some restrictions on the maximum motor or propeller size. Most frames that you can buy will also give you some recommendations as to what motors you should use to give you an idea of what to look for. I will also then add the weight of the camera and gimbal I want to use.

Thrust to weight ratio

With multi rotors its important to make sure that your motors can produce around 50% more thrust than the total weight of your drone. Or in other words your drone should be able to hover at just over half throttle. This is an important rule to follow is it means that you motors will have enough extra thrust to control your multi-rotor in wind and during aggressive flight maneuvers. If you are always going to by flying gently and smoothly increase the weight so that you hover at around 70% throttle for a less responsive drone. So if your total weight of your quadcopter is 800g, your motors on a quadcopter will need to produce 1.6Kg of thrust in total, or 400g max thrust per motor.

For miniquad racing, you would want a very agile quadcopter, so having a much higher thrust to weight ratio is desirable, but for an aerial photography drone that we will be flying gently, you could get away with lower power to weight ratios, but in general I would say that you should plan your build at around a 2:1 power to weight ratio, as you can always use the extra remaining weight to add bigger batteries to fly for longer.


Worked Example - A rough weight estimation

Lets say we want to build the miniquad as described in this silver blade miniquad build guide. We will start by deciding what frame we want to use, and in this case its the silver blade 37. The product description suggests we use an 1806-2204 size motor so by looking around on the internet we can get an average weight of this class of motors which is around 100g (which is actually abit of an over estimation). Simiarly 3-4S Lipo batteries that are around 1300-1800mah are commonly used with miniquads so we will base our battery weight on that size. The summary of the weight estimation is shown below, remember this is just a very rough estimate that we start with.

  • Flight Controller - 15g
  • R/C Receiver - 15g
  • Silver Blade Frame - 150g
  • 4x Motors and ESC - 200g
  • 3S LiPo Battery (1300-1800mah) - 150g
  • FPV Camera and Transmitter - 50g

So the weight of our drone will be around 680g so we need to have motors that can produce at least two times the amount of thrust in total (1.2Kg of thrust in total), however if they can produce more we will probably be able to fly faster. Since we are building a quadcopter, each motor must product at least 300g of thrust each.

If you do find this process particularly hard the best place to start is to look around a dronetrest, or the internet for other drone pilots who have shared their information on a drone build similar to yours, you can then base your weights on the parts they used. Or you can always ask for some help and advice on our help section

Reading that data

Based on our weight estimation we know we need to find a motor capable of producing a maximum thrust of 300g each, By inspecting the thrust tables of each motor you will gradual find a few motors that have the required thrust performance. In this case we have come across the data for the MT2204 motor which looks promising.

If you find it hard to know where to start, the best thing is to find a build guide, or quadcopter similar to the one you are building so see what motors and other equipment was used that you can use as a starting point.

Checking the thrust
Now we can get on with investigating and extracting useful information from a table such as the one above to find our quadcopter motor. We can see that this manufacturer has tested this motor with two different voltages (2S (approx 8V) and 3S (approx 12V) battery), and a number of different propellers (called paddles in the above table :blush: ). We are then given the amperage that the motor pulls, the thrust that it produces and the efficiency (thrust in grams/power in watts), as well as some other information. We can see from the table that with a 3S battery, these motors will produce enough thrust with 5x3, or 6x3 propellers which produce more than the required 300g each.

Comparing the efficiency

So, the first port of call is arguably investigating the thrust produced by the motors. To further differentiate between motors, it is my belief that efficiency should next be considered. The efficiency is commonly expressed as the thrust divided by the power used in watts or g/W. The more efficient a motor is (or the bigger the g/W number is), the longer the copter will fly. A general rule of thumb would be anything over 7 for efficiency is good, and of course, the higher the value the better. Some of the larger motors (BE 8108) have an efficiency (g/W) of over 18!

Once you have found several motors that produce the required level of thrust an easy way to choose the best one would be to get the most efficient one, but this will also usually end up being the most expensive one.

However, as mentioned previously in this article, this may not be your priority. You may want small, agile copter for acrobatic moves in the air, in which case you want high rpm, and the efficiency will necessarily take a hit which is usually the case for high KV motors. In our example we are choosing a motor for a miniquad, so the type of motor you would use for these copters is one like the MT2204, the table of which is shown above. This is why the efficiency of this motor is relatively poor.

Matching an ESC to your motor
Now that we have confirmed that this motor is suitable for our application, we look at the Amp draw for our chosen motor/battery/propeller. In our case, this is maximum of 7.5A for a 5x3 prop, and 11.5A for a 6x3 prop. Since in our build we chose the 5x3 propellers, so we will need to use an ESC that is rated over 7.5A, so an 12A ESC would be a good choice for this motor/propeller running on a 3S battery.

Refine the weight estimate to choose a battery
Now that you have chosen some components you will be able to update the initial weight estimate as we have actual weights of components. Based on these motors producing a max thrust of 310g with 5x3 props, our quadcopter should weigh less than 620g. The actual weight of all the electronics and the quadcopter frame come to 368g so that means we can get a battery up to 250g in weight. If you find that you dont have enough weight left over for a decent size battery you might want to go back and choose larger motors, or use larger propellers.

Instead of using all the remaining weight for a battery, a slightly lighter battery at 160g (tattu 3S 1800mah) was used so that our quadcopter will have more agility for racing. The actual brand will depend on your preferences and budget, but for more information you might want to check our LiPo battery buying guide

Hope that helps you when it comes to choosing a motor for your drone. If you have any questions please let me know. If you want some advice before buying anything you can also ask on dronetrest and myself, or someone else will be more than happy to give you some suggestions :smile:

This article was co written by Alex (@unmannedtech) and Sam (@Sam)


Brushless motors - how they work and what the numbers mean
What to consider when buying a ESC for your multirotor
How to choose your multi rotor Motors/Props/ESC
Autopilot and Drone Choice
How to read motor thrust performance tables
Which motors for a 6Kg Drone Build
LiPo Batteries - How to choose the best battery for your drone
Tricopter motors
Building Drone from Scratch
Building Drone from Scratch
QAV210 Spare Parts Question
Making a drone for farming purpose
Want to buy motor for drone
#2

A post was split to a new topic: DIY quadcopter for $250


#3

hi i am looking at building a drone that flies for 1hr and can carry 5kg-15kg any tips would be very welcome


#4

Best to start small and work your way up. If this is your first drone build, best to start with an off the shelf kit to get familiar with the basics, as building a drone that can lift that much weight and fly for that long will be very expensive as motors that powerfull cost at least £200ea


#5

i have six drones on the way to me so by time i have built them i will have the skills needed to achieve my goal of building these but not the tec knowledge so any help is still welcome


#6

Cool, well if you are not sure about something specific just post your question here and one of us will help. And if you want any tips it would be best to create a build log over in our build log category and show us all how you are progressing in your build and what you do in each step and if something is not quite right I am sure one of us will point it out to you :slight_smile:


#7

<img src="/uploads/db5290/original/2X/e/e40ea0a66e47edb3c7a768194b80ffd54201a1c0.jpg" width="690"height=“460”>

If I use a 12rib umbrella, each motor needs to lift 6kg. Is there motors that big?


#8

:slight_smile: as a matter of fact some manufacturers such as T-Motor have heavy lift motors such as the U13 which can produce a maximum of 10Kg thrust, but they cost about $380 USD each.


#9

Hello, informative post thanks a lot.

I’m thinking about building a quadcopter, I’m estimating a frame + components of 1 KG, i’ll add 20% just in case I want to go with onboard camera.

So, I’m trying to find out how much thrust each motor needs to provide as I want to hover about 50% of throttle.

1000 grams X 2 X 1.2 (the 20%) = 2200 grams total
2200 grams / 4 motors = 550 grams

I just wanted to know if I’m right or there’s anything I’m missing.
Would you please suggest me a good motor for this kinda weight.
PS: the quadcopter I’m building is not a racing one, rather a photography quad if I can say, no need for agressive manoeuvres. Thanks


#10

Hey, your sums are totally reasonable and correct. The 50% hover rule is for general/aerial photography drones to get maximum flight time. Many racing drones can hover at about 10%throttle as many motors are crazy powerful.

But for motors for your application I would probably suggest you go for something like our mt3510 motors with 15inch props if your frame can accommodate that?


#11

Hello, I want to build a drone with a motor KV rating of 2k-3k and an efficiency level that will let me fly for about 30-40mins on one battery without overheating the motors, I want this to be a very good racing drone so I would like to ask for help on which motor to buy can you recommend one to me please. The thrust has to be 1600<grams and I can pay up to £30 for 1 motor.


#12

Hello

Amazing details.

I was wondering how to measure the RPM of each motor accurately. I came across Hall Effect Sensors but have no idea on how to install or use them. Do you possibly have a link to that where you might have explained

Also is there a complete guide and explanation for parts where i could start from , from ground zero??

Thank you. A complete noob here… :slight_smile:


#13

You could look at getting a tachometer as they are abit easier to use than a hall effect sensor, but u have to have props attached. Eyare relatively cheap from your rc shot or ebay/amazon

And thanks for your kind words trying to add info all the time but writing a good guide takes lots of time. But this is a good place to star to know the parts for a drone


#14

hmm… im no expert but one hour flight time would require a massive battery, and getting 15kg of lift would require some massive motors. if you haven’t built one before this seems pretty ambitious, and very expensive. To start I’d look at the power draw of a hexa/octocopter and see if it is feasible to make something like this without breaking the bank at over $1k. Good luck :slight_smile:


#15

@unmannedtech

Dear Alex,

I’m quite confuse with the thrust number
Some websites shows the thrust of the motor as related to the % of throttle, show for the same propeller, the same voltage, there are still 2-3 number indicating the motor’s thrust value: http://www.miniquadtestbench.com/assets/components/motordata/motorinfo.php?uid=144

So which one should I use? the one with the 100% throttle?

Thank you!


#16

Ideally you want to hover at 50%ish throttle so.use those values to choose a motor rather than the maximum throttle


#17

@unmannedtech

Thank you Alex!

I’ planning on a build as followed:

As you can see, I haven’t decided my motors yet, thus, no ESCs & Batteries is added yet to the list

I’m considering the Racerstar BR2205 2300KV sold on banggood.com at the moment.
Their thrust rating is way over what I needed, but they’re the one with the best price I can find. Emax MT2204 or MT1806 motors are even more expensive!

I’ve asked some other people and they advised me to go for the Racerstar or the Emax RS 2205 S, which can have a lot of excess power for my quad. They said I can always tame it down in the flight controller setting (I haven’t looked at that yet, but I saw there’s a way to tame it down using “motor gain” in BLHelisuite), but if I’m lack of power, then I must upgrade my hardware which is very inconvenient.

Is that true? That I should go for powerful motors?

Note: I’m aiming for the 3:1 or 4:1 thrust to weight ratio, not because I really want the super fast responsive throttle performance, but because I’m going to upgrade and add more weight onto it.

Thank you!


#18

Hello
Quite informative post , thanks
I want to build a quad for racing ,the weight of copter is below 700 grams and i am confused with the size of propellers. I chose 2300 kv motors. please help me by suggesting the propellers below-

  • 6 X 3 , 2 blades
  • 6 X 3 , 3 blades / 4 blades
  • 5 X 3 , 3 blades
  • or any other size of your suggestion.
Also i wanted to ask that in determining the speed and swiftness of my copter would depend on the thrust or the rpm provided by motors?

#19

Helpful. Thanks a lot for the information about motors.


#20

i want to made a racing drone .
which size will better ??
what kind of motor i should use to make it faster