I’ve historically found advertised KV’s to be a bit off from real world values and wanted to start a discussion of everyone’s personal experience. This can hopefully shed light to various motors from various manufacturers and help builders purchase correctly with eRPM in mind.
This was a topic I saw talked about for a bit last year. Although the comment I’m linking is purely anecdotal, I saw some users test the KV themselves as well which resulted in lower kv’s than advertised.
In regards to @chaka’s motors. He kindly shared his methodology of calculating kv from VESC real time data which you can find here. The gist is [Power / Motor Current = Motor Voltage], eRPM / 7 pole pairs / Motor Voltage = KV @ 95% duty cycle. Since the VESC only runs at 95% duty cycle max we finally divide by .95 to get the actual KV of the motor. As you can see from the link, chaka’s calculations were pretty on point lending a result of 197kv for his 200kv motor.
I’ve applied the same math to @JLabs Polar motors (and soon @Kaly’s motors when I get them) and found that his 190kv 6355 motors have a calculated kv of 179kv. A bit lower than advertised, but this makes it easier to apply to higher voltage setups without too much worry of hitting eRPM limits.
For the above example 42W / 1.21a = 34.71v. 41309erpm / 34.71 / 7 / .95 = 178.96kv
If you’re willing to test your motors out, please post your results here so we can gather data about motor KV’s! If I get enough responses, I’ll start a Google Sheet for it. If you’d like to contribute but aren’t sure how to get the values, post a screenshot of your real-time data tab while under full throttle and I’ll do it for you!
TL;DR: Some motor KVs are lower than advertised, let’s gather data here!
- chaka’s 200kv motor = 197kv calculated
- Jlabs’ Polar 190kv motor = 179kv calculated
- Kaly’s 230kv motor = 200-210kv calculated (20 samples)