Product Tips & Tutorials: Motors
Brushless Motor Rating
Posted by on 31 August 2012 12:21 PM

KV Rating

KV rating is referred to the RPM of the brushless motor per volt. This rating is determined without load. If you're wondering what "load" is referring to, its if there is weight, or a load, that the motor is pushing/pulling/moving. If it does have weight attached to it, obviously the RPM will be different.

Here is a very general KV Rating for Brushless Motors.

Micro size: 4000 low 160000 high
1/18th: 3000 low 7800 high
1/10th: 2000 low 6000 high
1/8th: 1050 low 2000 high
1/5th: 700 low 900 high

You take the KV rating of the motor, and you multiply it by the voltage of the battery to get the total RPM.

For Example: A Brushless Motor with a KV Rating of 3500 and you're using a LiPo battery that has 11.1 V, the equation will look something like this:

3500 (KV) x 11.1 (V) =  38,850 RPM.

Another thing you should understand about the KV is that the higher the KV rating, the faster the motor will be, but it will have less torque. The lower the KV rating, the higher the torque. So what does that mean? High KV = High Top Speed but Low Acceleration. Low KV = Low Top Speed but High Acceleration. 

Watts/Amps/Current

Watts are the power rating of your brushless motor. Every 100 Watts = 1lb of weight movement. In other words, 100 Watts can move 1 pound. You find the Watts by multiplying the AMps with the Battery Voltage. Usually you can find the Watt, Amp, and Current rating of the brushless motor on the Spec Sheet or User Manual that comes with the motors. Most of the times, they will show it on the box as well, since this is all important information when buying your motor.

This bit of information is extremely important for aircrafts. Planes, helicopters, quadcopters are all weight dependent. If a motor does not have produce enough Watts to move the weight, then there is no way that the aircraft can fly. So remember to keep this in mind when you buy your motor.


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