Basics of RC Electric Motors

Picking RC electric motors is not as easy as just buying the recommended Motor size. There are lots of different brands, specifications, and sizes, which make it very confusing to know what motors are going to work. Understanding the basics is important, so you can make better decisions about the motors that you buy. This guide will help you understand the basics of RC Electric Motors.

Brushed Motors Vs Brushless Motors

Brushless Motors are the more commonly seen type of motors since they create more power, and do not wear out as fast as brushed motors. There are still brushed motors on the market, but most are brushless because they work longer and better.

The Specifications of Motors

When you are shopping for RC motors, you need to know what all the specs and numbers are on the motor, and if it the recommendations. The wrong spec could lead to you to damaging the rest of the build or the item not having enough power.

VOLTAGE CONSTANT

Voltage Constant is listed as Kv. Kv is the RPM that the motor creates per volt which is applied. In reality, the number is a tiny bit less since motors are not 100% efficient outside of labs. An example is applying 12 volts to a motor that is 200Kv, would turn into around 2400 RPM’s.

TORQUE CONSTANT

Torque Constant is Kt. Kt=1355/KV is what all motors have. There is a lot of science behind the 1355, so its better not question why that is. The simple explanation is that the faster a motor spins for a voltage (Kv), the lower amount of output torque is (Kt).  This means that outrunner motors will normally have lower Kv, so they have more torque, which makes them great for larger RC props. The opposite is true for most inrunner motors.

NO LOAD CURRENT

No Load Current is Io. This number is the amount of current that the motor needs to spin without a prop. Io should be subtracted from the total amount of Amps that the motor uses to find the amount of Amps that you have to move the prop.

TERMINAL RESISTANCE

Terminal Resistance is Rm. Terminal Resistance is the resistance inside of the RC motor and is measured in Ohms. The higher the number attached to Rm, the overall less efficient that RC motor is.

Power and Current

The power and maximum current is what will determine how big of prop, and size of the RC unit that can be used with that RC motor. To get the power, multiply the maximum current with the battery voltage. This important to get the right amount of power outputs, as if the motor needs to draw more current than its limit, you will destroy the motor. This can lead to smoke or fire depending on the motor. It is better to go with a little extra maximum current rating, just to be sure that you will not damage the motor with your prop.

How Much Power Does Your Motor Need?

Thankfully, most manuals for RC kits will come with recommendations for specific RC electric motors. Most times, the recommended motor will be from their brands or from a brand that they are affiliated with. If you want to use a different motor, all you really need to do is compare motors with similar Kv ratings and power outputs. This information will be on the box or the web store page. Comparing online is easy since there are tools and guides for similar RC motors.
If you are not using a kit that comes with information or building a RC unit from scratch, you are going to have estimate the amount of power your unit needs.

Many people in the RC world accept 100 Watt/lb is a good estimate of the power needed for the average RC unit. The amount of power that you are going to need is affected by what you plan to use the unit for. If you are looking for a faster RC unit, you may want to bump the power estimate up to 150 or 200 Watts/Lb. However, if you are not really sure, then 100 Watts/Lb will get your unit running.

The Other Components

Having the right motor is just one piece of your RC unit. You also have to pick the right size battery and electronic speed control. These items are affected by the motor and the RC unit as a whole. Luckily, if you are building a kit, there will be recommendations about what you should buy.

The more experience that you have with RC electric motors, the more knowledgeable that you will become. Understanding the basics can help you buy motors, but it will not help you know what the best motor for your project is. Trying different motors and set-ups is the best way to learn what the best motors are.