Choosing a brushless motor for an RC plane or quad is quite a tricky process for new pilots. Here's what the differences are.
If you’re wanting to upgrade your brushless motor(s) on your favorite model or quadcopter, or need one for your latest scratch build, you may want to know what the differences between various options are. Here's what the numbers mean so you can choose wisely.
Power Packs
If you're a newbie to the RC hobby, you might not be aware that we stock complete hassle-free 'power packs' designed to a range of models and quads. These include all of your airplane electronics, excluding a receiver and battery. You can view our full range on the FT Store. There are also specific articles covering the details of four of our most popular packs that you can read here:
Power Pack A - For Mighty Mini Airplanes
Power Pack B - For Lightweight Airplanes
Power Pack C - For Powerful Airplanes
Power Pack F - For Powerful Mini Airplanes
Inrunners and Outrunners
It might be worth mentioning that there are two distinctively different types of motor you can get your hands on. One is an inrunner and one is an outrunner.
Inrunners = motors where the shaft rotates inside the outer casing of the motor. Usually used in RC helicopters.
Outrunners = motors where the whole outer casing (attached to a shaft, propeller or both) rotates around the center.
Speed
As you might expect, motor speed is connected to how fast you want/need your plane to go. To compare speeds, you're going to want to look for a KV number. KV = revolutions per volt. For every volt that's fed to the motor, in a no-load condition, the number is how many times the motor would turn. This also means that increasing the voltage will make the motor spin quicker. The motor pictured below is 1200KV.
Size
The physical size of a particular brushless motor is usually indicated by a number that looks like this - '22-05'. The first number, 22, indicates how wide the motor is whilst the second number, 05, indicates the hight. Usually, these are written on the motor casing themselves to show you how wide and high they are. Generally speaking, wider motors produce more torque as they have more leverage.
Power
The overall power of a motor tends to be indicated by Watts. This is Voltage x Amps. The higher the number, the more powerful it will be. You'll also need to make sure to specifically check how many Amps that a motor pulls in order to find the right Electronic Speed Controller (ESC). Use an ESC that is at least 20% larger than this number. If you have a motor that pulls 20A, a 30A speed controller would work fine.
Thrust
Much of the time, you can how much thrust a certain motor produces with various propeller and battery combinations. This information can be used to find the perfect sized motor for your model. If you want to go vertical with a model that weighs 2lbs, make sure to get a motor that produces over 2lbs of thrust.
Choosing motors can be a little challenging and confusing at first, but knowing what these numbers and statistics actually mean can help a lot.
If you learned something from this article, remember to give it a 'thumbs up' so others find it too!
Article by James Whomsley
Editor of FliteTest.com
Contact: james@flitetest.com
YouTube Channel: www.youtube.com/projectairaviation
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Be sure to use the recommended voltage, meaning 2S, 3S, or 4S etc. where each S is the number of Lithium polymer cells in series. Each cell is nominally 3.7v.
If you use a higher voltage then you will need to use a smaller diameter and/or pitch propeller, otherwise you will overload the motor and it will get hot and run inefficiently.
Be sure to monitor the temperature of your motors. If they are too hot to touch after 30 seconds at full throttle then you need to use a smaller propeller. Ideally they should not get much more than warm. Likewise your ESC should not get much more than warm. Heat is power not making the plane fly faster.
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