The most important part of your quadcopter is your motors.
You can have the best flight controller and ESCs in the world, but when it comes to flying, your motors will actually be spinning your props. And if you pair a 4S lipo with motors that can’t handle the voltage, you’ll be seeing some magic smoke very soon.
So while good motors may seem expensive(at $20 per motor, times 4 motors, you’re looking to spend around $80), they’re absolutely worth it.
Before I dive into(har har) how to choose your motors, I’d like to share a little story about choosing underpowered motors. When I ordered my ZMR180, I ordered the ARF kit that came with 1806 motors.
Very soon, though, even 1806 on 4S seemed underpowered – plus my motors were coming down really hot. It seemed like I should have spent the extra few dollars and bought 2204/6 motors instead.
Now, since my frame can only fit 18xx motors, I need to upgrade both my frame and my motors. Sucks for me!
Motors for different size quadcopters
Ok, so the heading should actually read “motors for different size propellers”. But since the size of propeller you can spin is directly related to the size of your quadcopter frame, it’s close enough.
Generally speaking, you want to choose motors that balance 2 things:
- The ability to spin any given propeller as efficiently as possible
- Weighing just the right amount for your build size
Spinning propellers efficiently
You already know that motors come in different kV ratings. The kV rating is based on how many windings of copper wire there are in the motor.
Grossly simplified, kV is how many revolutions per minute for each volt of power you provide.
So a 2300 kV motor on 4S(16.6 volts fully charged) will spin at 2300 x 16.6, or 38180 RPM.
Well, not exactly 38180, but that will get you a close enough estimate.
For a more mathematical explanation, check out this excellent post.
Of course, when you load a propeller on to a motor, everything changes. Not every prop will spin at exactly 38180 RPM – you’ll have to factor in air resistance, the length of the prop, and the pitch of the prop.
The other factor to spin propellers more efficiently is the width and height of the motor.
To simplify things, the more the width of the motor, the more torque it has to spin a propeller – so it will increase its efficiency.
So will the height of a motor. However, after a certain height, the motors will get too heavy, and RPM will start to decrease again – at one point, the returns will start diminishing.
For example, a stator height of 6 mm will be more efficient than 5mm, which will be more efficient than 4mm, when all the motors have a kV rating of 2300. However, the most manufacturers have pushed 2300 kV is on a 7mm and recently 8mm stator – you won’t find a 10mm motor with such a high kV rating, because the weight will be far too much.
What do the numbers on a motor mean?
Of the four digit number you see associated with motors, the first two numbers are the width of the motor.
A 22xx motor has a stator width of 22 mm.
An 18xx motor has a stator width of 18 mm.
The second two digits are the height of the stator.
A 2205 motor has a stator height of 5 mm.
An 1806 motor has a stator height of 6 mm.
The next 4 digit number, as you already know, is the kV rating.
General rules for motors and props
Micro quadcopters are suited to use 11xx and 13xx motors.
11xx and 13xx motors most efficiently spin 2.5 and 3 inch props, though you could get away with spinning 4 inch props on a 13xx motor.
11xx and 13xx motors are usually rated 3100 or 4000 kV. If you are planning on using a 4S battery, stick to lower kV.
There are also 6500 kV 11xx motors, which can only be used on 2-3S and give solid punch to ultra-micro builds.
Recently there have been 7000, 8000, and even 10000 kV motors which are used on ultra-micro builds.
There is a wide variety of mini quadcopters, starting from a 170-180 wheelbase that can fit 4 inch props, going up to 190-230 that is suited for 5 inch props, and finally 250-260 that can fit up to 6 inch props.
Best motor for 4 inch props:
The best motors for 4 inch props are a simply finding a sweet spot of light weight and lots of power. Older 4 inch kits used to have 22xx motors or 18xx motors, but the trend nowadays is using 14xx motors, which actually have more power than the older 18xx motors.
- 1407/3xxxkv motors with a super light frame will be a BEAST on 4S, great for staying under weight limits
- 18xx/2300kv motors for a decently zippy build on 4S, but will have trouble lifting a GoPro or Yi
- 22xx/2300kv motors for a really fast build on 4S, can easily lift a GoPro or Yi
- 22xx/2700kv+ motors for a beast
Best motor for 5 inch props:
- 18xx/2300 kv motors for a first build that you can run on 3S or 4S
- 22xx/2300 kv motors for a nice racer that will be the perfect balance of speed and agility
- 22xx/2700 kv motors for a beast that will kill your lipo if you are not careful!
Best motor for 6 inch props:
- 22xx/1900-2000 kv motors for a 4S build that’ll be super fast
If you are using a low pitch propeller, you can get away with a higher kV and still not lose that much efficiency.
As a rule, remember that higher pitch propellers will generally generate more thrust and pull more amps than lower pitch propellers.
So if you use a high pitch propeller on a high kv motor, you’ll draw more power.
Here are some good motor/prop combinations:
For 1104 motors, the standard prop is a 3020.
For 1306 motors, you can use anything from a 3030 to a 3545 triblade. If you are using greater pitch, make sure you’re using the low kv motors, especially on 4S.
For 1806 motors, you can use anything from a 4040 to a 4045BN on 4S(4045BNx3 will superheat your motors). You can also use 5 inch props from 5030 to 5040 – I wouldn’t use 5045BN or triblades on 1806 motors.
For 2204/5 motors, you can use anything from a 5040 to a 5045BNx3 – but if you’re going to use a 5045BNx3, make sure you are no higher than 2300 kV. You may be able to push it with 2700 kV, but you’ll drain your battery super fast and your motors may get hot.
There are also the RaceKraft 5051 props which people have been really happy with, but I have personally not tried them.
The thing about props is that once you’re comfortable, don’t change them on a particular build – if you’ve got the budget, use another build for different props – once you’ve tuned and gotten a quad to fly the way you want, it’s not fun to tune it all over again to new props.
A note on weight
Hypothetically speaking, the larger motors can easily spin smaller props, but at the added cost of weight. 1104 motors weigh about 6 grams each – ideal for a tiny micro build. 1306 weigh about 12 grams, still not bad for a micro as long as you’ve got good enough props.
However, the 2205 motors from DYS and Emax that are so popular right now weigh 30 grams each – so you’re looking at 120 grams for four motors, which will be way too heavy for a micro.
This was an exaggerated example just to demonstrate a point.
Getting all of the information
Different brand motors will similar stats will all produce different amounts of thrust. Even the same motor, using the same pitch and length propeller(of different brands) will give you different thrust results.
When you are researching a motor, I suggest you search YouTube and RCGroups for thrust data. Miniquad Test Bench also has really in-depth tests for most of the popular motors.
Look at the amount of thrust the motor produces on a given prop, at a given voltage, and how many amps it draws. You have to make sure your battery will be able to provide enough amps – and your ESCs will be able to handle that many amps!
Realistically, you won’t be flying at 100% throttle ever(maybe you’ll push it to 80-90% for a few seconds every now and then), so you’ll actually be drawing far fewer amps, but you need to be prepared for extremes.
You may find that one motor draws fewer amps on a specific prop but gives more thrust than another motor. Check out the resources above before you buy, and you should be fine.
My picks for motors:
- RacerStar 1104s(choose the kV yourself) for super-ultra-light micros on 2S
- DYS 1104 for ultra-light micros on 3S
- Emax RS1306 kv for micros on 4S
- Emax RS2205/2600 kv for minis running 4 inch props
- DYS SE2205/2300 kv for minis running 5 inch props
- Lumenier RX2206/2350 kV for super smooth and efficient 5/6 inch builds
- RacerStar 2205/2300kV for tight budgets(4 of these cost the same as one Lumenier)
Note: There’s no shortage of good motors – there are the Cobra championship motors, ZMX fusion motors, TBS Mr Steele motors, and so many more. The ones listed above are my opinion, and other pilots will most certainly have other preferences.
For information on motor tests and thrust data, check out Mini Quad Test Bench.