#1 Brushed Vs. Brushless
The older brushed technology is inferior to brushless in many ways, but it still has a place. Brushed motors are simple in design with their two-wire control. They’re also quite reliable and cost much less than the brushless alternatives. Another advantage is that they’re highly configurable. These things combined make them an attractive choice for novice RC pilots and those who like to tinker.
Brushless motors may cost more, but they last longer because there are no brushes to wear out. They have better power efficiency as well. These motors are quieter as they don’t suffer the same electromagnetic and electrical noise. So, the advantages of brushless motors are less maintenance, fewer problems, and cost savings in the long term.
#2 Inrunner Vs. Outrunner (Brushless)
Inrunner and outrunner motors are not the same, so which is best? Let’s compare:
- Inrunners: The shaft rotates on the inside of the motor’s hub
- Outrunners: The entire outer hub spins around the center
The best option depends on flying styles and expectations. Here’s a side-by-side comparison:
| INRUNNERS | OUTRUNNERS |
|---|---|
| High Revolutions per minute (RPM), low torque More energy-efficient Need a gearbox to function Wider propeller selection Noisier than outrunners | Low RPM and higher torque Less energy-efficient than inrunners Don’t need a gearbox to function Narrower propeller selection Quieter than inrunners |
Inrunner motors turn the fastest out of the two, which makes them more efficient. However, the extra internal parts also mean there’s more to go wrong. The gearbox shafts bend easily, and the gears eventually get stripped. Inrunners are often—though not always—the preferred option for RC helis.
#3 How to Determine Motor Size
A simple height/width number tells us the size of RC motors and is usually printed on the casing. The number may look something like this, 2204 or 22-04, but it’s the same reading. The first number “22” is the motor’s diameter, and the second “04” is its height. Wider motors produce the most torque.
#4 How to Determine Motor Speed
The quicker the motor, the faster the potential is for your RC heli or other aircraft. The way to identify the speed that an RC motor turns is to look at the KV number. It tells us the relationship that links volts to revolutions per minute (RPM). Let’s use KV1000 as an example. This number means the motor spins at 1000 RPM per 1 volt. There are 2 things to consider with the KV numbers:
- Lower KV: Spins slower but provides more torque
- Higher KV: Spins faster but has less strength
Point to note: RC engine manufacturers tend to be overly optimistic with KV numbers.
#5 How to Determine Motor Power
AMPS (current) x VOLTS = WATTS (the motor’s equivalent to horsepower)
The “watt” is a unit of power named after the inventor of steam engines, James Watt. The watts of an RC motor determine its power. Watt ratings are found on the motor’s spec sheet. Higher numbers mean more power. Check the motor’s amps to find the correct Electronic Speed Controller or ESC. Opt for an ESC current value that’s 20% or more than the motor’s current value.
Keep the following points in mind:
- GOOD: ESC AMP capacity 20+ percent or higher than the motor’s draw
- BAD: Motor AMP draw is equal to or larger than the ESC capacity
- The flight battery must supply the burst AMPS the motor’s rated for
That’s the basics covered. The second half of this page looks at some real motors for RC helicopters of various types and sizes. The maker’s specs should now make a lot more sense.
