Brushed motors are usually rated just in terms of the number of Turns. This relates to the number of turns of wire on the motor armature as we discussed in our earlier article, an in-depth look at motor turns. But when it comes to brushless motors, there’s another rating that needs to be taken in account, and it’s known as the KV rating.
When buying Brushless Motors for RC Cars you will often see a KV Rating being quoted alongside the number of turns. The KV rating is quite simply the number of revs per minute the motor will produce per Volt of electricity that’s applied. So a 3000kV brushless motor will output 30,000 rpm when you apply 10 volts to its terminals.
Racing specification motors are typically rated anywhere from 3000kV right up to 9600kV or higher!
As with brushed motors, there is a trade-off… There’s always a trade off. Just as the higher the turns in a brushed motor, the higher the torque, similarly the lower the kV rating in a brushless motor, the higher the torque. The higher the kV, the higher the rpm but this is at the expense of torque. So a larger RC Car with a high kV motor may have a high top speed, but it will slower of the mark than one with a lower kV rating.
For lightweight 2wd buggies, a motor with a high kV rating (6000+) will give you the best of both worlds, high speed and good acceleration. Similarly, a larger, heavier RC Car or truck such as a Short Course truck would be better off running a mid-range kV rated motor such as a 3500kv to give you good torque, excellent acceleration and a more than adequate top speed.
So, quite simply:
- Kv Rating is the number of revs per 1v applies
- High KV = High Top Speed / Low Torque
- Low KV = Low Top Speed / High Torque
Don’t forget, as always, if you have any questions or comments regarding the topics covered in this article, please feel free to post them in the comments below