Choosing a quadcopter motor is tricky.
The real problem with choosing a quadcopter motor is that there are just too many variables:
- you can choose a motor, which will affect both the quadcopter’s weight and the maximum thrust, so you may have to repeat the selection process
- you can choose a frame plus battery, but then it’s hard to find a motor which can lift it
- the propeller you choose will affect the maximum thrust, and the power requirements too (which in turn affects the motor, battery and ESCselection)
For mini and nano quadcopters which measure less than 180 millimeters diagonally the usual choice is a brushed coreless motor.Quads larger than size 250 use brushless outrunners – these are the real deal, as these motors have more power and better longevity than the smaller brushed motors.
Manufacturers usually mark these motors with four numbers, for example”2210″. The 22 means the stator’s diameter, while the 10 means the stator’s height. These numbers are not that important, as they do not describe the motor’s performance, just help you get a ballpark figure.
Quadcopter motors have three important parameters.
The most important parameter is probably the KV value – the KV value helps you find the motor’s RPM for a given voltage. All you have to do is multiply the the KV value with the motor’s input voltage, the result will be the RPM. This is important because a lower KV motor will suit larger quadcopters better, while a higher KV motor is better for smaller quads.
The next value that’s important is the efficiency.
Just avoid motors with low efficiency numbers, as these will turn your precious battery charge into heat, instead of driving the props. So go for a motor with as high efficiency as possible to get most out of your quadcopter. Efficiency numbers over 90% are common nowadays. This means that for every watt pumped into the motor, 90% of it will go towards rotating the propeller, and 10%will be turned into heat.
The third most important parameter of the motor is the maximum Ampsit accepts.
The maximum Amps the motor can handle depends on it’s wiring, while the maximum Amps you need depends mainly on the thrust you need, and the propeller’s efficiency. You will have to choose your ESC depending on the Amps you need too, however this is easy – just go for anESC which can supply 2x the Amps you’d need at full thrust to make sure it won’t burn out.
A good motor is nothing without an appropriately sized prop.
For your quadcopter to fly well, you will need an appropriately sized prop.Propellers have two parameters, the diameter and the pitch. The diameter is the prop’s diameter, while the pitch describes the tilt of the blades. For example a prop with a pitch of 4 is tilted such that the blade would be 4inches high if it reached around the center hub.
There are two ways manufacturers mark their props. A prop with a 5 inch diameter and a 3 inch pitch could be marked either as an 5030 or an 5x3prop.
If you’d like to maximize flight time, go for the largest prop you can fit on the frame. If you’d prefer to have an agile quad, select a prop that’s just one size smaller. For example if you have aZMR250 frame, an 5030 prop could be the best choice, while a 6040 prop would probably still fit.
When sizing your motors and propellers, go for a combination which would provide you with 2 time the thrust
of your quadcopter’s weight. This ensures that your quad will be able to keep balance, fight the wind and fly the way you want it to.
At this point you have probably chosen what you want to build you just do not know what motor would fit the best, that’s why you are here 🙂 To start, you should find out the usual weight of the your model – for exampleZMR250 based quadcopters usually weigh around 500 to 600 grams. A quick google search will help with this one.
Next you should find out what is the largest propeller you can fit
on that model. Larger props are usually better from efficiency point of view. If you like DIY solutions, here you can get creative – reorganizing the frame can help you fit a larger prop. For example on a standard ZMR250 quad you can fit props up to 6 inches in size, while the 5030 prop is the one that’s usually used.
Once you have these details ready, head over to ecalc.ch.
The free version is a bit restricted, so you may consider signing up – if you build a quad you will spend an order of magnitude more on broken parts anyway.Open the xcoptercalc atecalc.ch, and fill in what you already have. You can get our annotated screenshot here. It’s a good idea to set the weight near the higher end of what you expect, never the lower end – it’s hard to build a light quadcopter, and it’s likely you will overshoot. Do not be afraid to choose an unrealistic setup at first – the idea here is to have something to start out, and improve gradually. After entering the weight, choose a 3Sbattery, let’s say an 3000mAh one, and an oversized ESC, let’s say a 90 Amps one.
Next, bluff your way through the selection process.
Select a motor manufacturer you know, next select a motor size you think could work. For this example I selected a DualSky ECO 2208C motor and an APCElectric 6040 propeller. Now this is not realistic, but we have a winner here – this thing would fly if we could reduce it’s weight. Ecalc is kind to us, and shows the errors in red right bellow the table.
If the bluff is viable, refine it.
In this example we got lucky, and all we need is to reduce the weight a bit.Replacing the 90A ESC with a 20A one does the trick in this case.
Do not stop here!
It’s important to collect multiple configurations that could work – it canv ery well happen that the 4th one will be the best. Try out bit smaller props, different motors and a 4S battery instead a 3S one and write down the details of each that’s likely to work.
Here are a few example setups
for different quad sizes. These are known to work, still it’s a great idea to double check the components.
Motor: Lumenier RX2206-11 2350Kv Motor
ESC: Lumenier F390 30A BLHeli ESC OPTO (2-4s)
Propellers: Lumenier 5x4x3 – 3 Blade Propeller
Battery: 1300mAh 4S
Size 220 #2
Size 250 #2
– this one is available as a set from Amazon.
Motor: XXD A2212 1000KV
ESC: generic 30A
Propellers: generic 1045
Size 450 #2
If you’d like to build your own quad, our How to build a quadcopter? article can be a good starting point. To make even more components at home, What is a DIYquadcopter?can give you great ideas. Oscar Liang has a great article on quadcopter motors too.