how to choose the power motor system for Freewing RC plane Xie zhao Ting
Written by Mr Xie (general manager of Freewing Model)
the first Airliner Airplane in a scale model manufacturer
Product review
As seen in the Feb,20th 2022 In China
Dear Friend:
What is KV?
When it comes to knowing how to pick the right motor for your RC plane, you'll also need to understand what KV means. KV refers to the number of revolutions per minute (RPMs) that an electric motor can spin at per volt when there is no load. So, what's the difference between having a high KV and having a low KV? Think of these differences as being similar to the difference between a high-performance racing two-stroke motorcycle engine and a standard Harley Davidson's four-stroke motorcycle engine.
While both the two-stroke and four-stroke motorcycle motors will use the same amount of horsepower, a two-stroke motor can do this at 11,000 RPMs. On the other hand, the four-stroke can do this at 3,000 RPMs. This comparison resembles how high and low KV electric motors also function.
If both motors use the same type of voltage, then a high KV in-runner motor that utilizes a small diameter propeller would work well in a high-speed model like a racer. On the other hand, a low KV motor that features a larger diameter propeller would work better for power, like flying a sailplane to its altitude.
You can figure out the KV of a motor by determining the number of winds or turns made by the propeller. The number of winds or turns means the number of times the copper wire goes around the stator pole. The more winds, the lower the KV. The less the winds, the higher the KV.
Lower KV or Higher KV?
So, what are some of the differences between lower KV and higher KV? We did mention a bit about this above, but we'd like to talk about this in more detail below. When you have a high KV motor, it will spin at a faster rate compared to a lower KV motor that is operating at the same voltage. So, if you are using a smaller voltage battery back, you might want to consider using a high KV motor. This concept is especially true if you like to compete and race, in which case a higher KV motor might help you.
However, if you don't have to worry about the limitations of a specific voltage, then you might want to instead use a lower KV motor at a higher RPM by initiating a higher voltage. If you tend to fly large out-runners that have a KV of 200 to 300, then you've got an excellent example of a good performing low KV motor. You'll also need to take a close look at the voltage limit when you are thinking about buying a new engine.
Choosing an In-Runner and a Gearbox
If you are opting to go with an in-runner motor, then you'll need to know a bit about how you can select and in-runner and an engine. While the process can be a bit challenging, if you take the time to educate yourself about how to make a good purchase, then you won't run into any issues. Selecting an in-runner and a gearbox is similar to picking an out-runner, but with an out-runner, you don't have to worry about the gearbox.
If you know you'll need to purchase an in-runner motor; you'll usually have two different options from which to pick. We'll use Feigao as an example. On the Feigao website, Feigao.com, you'll see all of their motors in a list and a full set of numbers for every engine. You'll even notice that Feigao includes different suggestions for setting up the motors. Feigao's smaller diameter motors are called ��380s,�� and their larger ones are called ��540s.��
Both the Feigao 380 and the Feigao 540 come in three sizes, small, large, and extra-large. Most of the Feigos work like copies of Hacker in-runner motors, with 380 translating into the B40 format and 540 translating into the B50 size. So, you can find a successful set-up if you want to copy it and do some Internet research. You'll also discover that the ratios for both Hacker and Feigao gearboxes are similar at 4:1:1 for the 380 sizes and 6:7:1: for the scale 540.
Related Post What Happens If An RC Plane Goes Out Of Range?
However, what does the ratio 6:7:1 mean? To figure that out, you'll need to know the KV of the prop shaft with a gearbox. To figure that out, you'll need to divide the motor's KV by the gearbox's ratio. If you need some help figuring all of this out, you can try the Peak Efficiency website. On that site, you can play around to figure out how your potential motor set-up will work with your RC plane. This website is helpful because it will give you an idea of what might happen as you play around with different options.
RC Plane Motors and Electronic Speed Controls
Now that we've given you more background information on both in-runner and out-runner motors, we'll talk about electronic speed controls, also known as ESC. In the RC model plane world, you'll discover that there are two types of ESC in existence, brushed or brushless motors. When it comes to this, you'll need to be aware of the fact that you won't be able to use a brushed ESC with a brushless motor, nor will the rule apply the other way around.
Because of this, you'll want to start by considering the different features you'll need for your RC plane's motor, like a decent brake or a soft start. You'll want to factor in a brake on your RC plane if you use a folding prop and a soft start. It's also a good idea to have a brake on your RC plane if you are also using a gearbox and a switch for on and off with the throttle. The types of features we just described are commonly found on RC sailplanes.
Match Your ESC to Your Motor
You'll want to make sure that you match your ESC to the motor you wish to when you select your ESC. If you're able to use an ESC that has a higher amperage than what you think you'll be using your motor at, you'll get some protection against stressing your ESC and damaging your RC plane. When it comes to an ESC, you'll see a burst rating most of the time, and that tells you how you can run your ESC at its maximum amperage for a short amount of time.
If you exceed that limit, you'll be doing damage to your RC plane. Most practiced RC plane enthusiasts like having an ESC that has ten to twenty percent more amperage than what they ever planned on using. You'll have to get a meter to help you measure the amps and volts your power system can generate. That will help you to ensure you aren't over-stressing your ESC, the battery, or your motor.
To help you better understand this concept, we'll describe what a BEC is in the RC plane world. A BEC is an acronym that stands for "battery eliminating circuit." So, a BEC is a device you can use to get power for the servos you have in your RC plane. Often, an ESC will have a BEC that can only work well over a specific number of servos and a particular voltage. The more you increase the voltage, then the fewer servos you'll be able to use.
On the other hand, if you use too many servos on your BEC, your ESC will wind up overheating and eventually totally failing. That can be terrible if your BEC fails in flight while your plane is in motion. So, purchasing an external BEC for your flight battery pack is an excellent way to ensure you've got what your plane can handle.
RC Plane Propeller Selection
Remember, the propeller does put a load on your power system. So, if you purchase the wrong type of propeller, you can harm your battery while also damaging your motor and ESC. Remember, props work much like a car's gear system. With some props, you'll have a first gear that operates at a high RPM to make the motor go slowly. At that rate, you'll have quite a bit of power but not a lot of speed.
If you want to go fast instead of having a lot of power, then you'll wish to a propeller that works more like a car's top gear. That means once you speed up your plane, it can continue at that rate for some time. If this is what you want, you should get a prop that has a diameter of about ten inches, and a total pitch of four.
Final Thoughts
When considering the perfect motor for your RC plane, there will be a few things you'll need to think about overall. Since different RC plane models function better with different types of motors, you'll need to educate yourself about the kind of engine that is best for your RC plane. Once you know that, you can use some of the calculations we provided above to help you figure out the best motor for your RC plane.
Once you've figured out the perfect motor for your RC plane, you'll be able to get hours of enjoyment flying your aircraft with friends and family!
