When you want to buy a new brushless motor for your RC truck, it’s only natural and pretty prudent to want to compare offerings from different brands. The only problem is the manufacturers don’t make it easy. Some market their motors by Kv rating and others use the term turns.
Kv is a measurement of performance. Think of how full-size manufacturers try to impress us with big horsepower numbers. While Kv isn’t horsepower, it does allow us to compare a performance attribute of motors. Specifically, Kv is how fast (rpm) a motor spins when one volt is applied to it. So, in theory, the higher the Kv rating, the faster the motor. For example, a 9000Kv motor would be considerably faster than a 2200Kv motor.
If Kv made us think of horsepower, turns reminds us of displacement. That is to say, like displacement, turns is a physical attribute of a motor. The number of turns indicates how much wire is wrapped inside the motor. A higher turn number means more wire which means more resistance which means a slower motor. So, turns is just the opposite of Kv in the sense that with turns a lower number means faster. For example, 4.5-turn motor would be considerably faster than a 15.5-turn motor.
What it all means
The bottom line is that Kv and turns are two very different things. One, Kv, is a measurement of performance output. The other, turns, is a physical attribute. Again, it’s like comparing horsepower and displacement. Generally, fewer turns means more Kv (speed). It’s just like more displacement generally means more horsepower. You probably know that all engines of the same displacement don’t put out the same horsepower. It’s no different in RC; just because two motors have the same number of turns doesn’t mean they have the same Kv ratings.
It’s unlikely you’ll find an RC company using horsepower to measure performance of its motors. This is because most RC brushless motors produce less than a single horsepower. A better measure to use is watts. You can even convert watts to horsepower.
Brushed and brushless motors are both measured in turns, but the numbers are not directly comparable. That is to say a 10-turn brushed motor does not deliver similar performance as a 10.5-turn brushless motor. For years, a 27-turn brushed motor was the standard of “stock” racing. The new standard is 17.5-turn brushless.
You can find more information on sensorless vs. sensored brushless motors here.