KV Rating Accuracy
 

Hello,

I recently purchased a HH Puller Pro XL 3500kv motor for my 1/10 Yeti. I am waiting on a vanquish motor mount to install, so I took a few moments to use the motor test that is provided in castle link. When i tested the motor, the KV rating was shown as 4141, which is significantly higher than the 3500kv rating. This would mean I am less than 10% away from the 50K RPM limit of the motor when running 3S, when at the stated KV I would be under 39K RPM. The stated rating makes 3S a safe choice and 4S a possibility if I keep an eye on the temps.

I also tested a Castle 1512 2650KV motor and got a KV rating of 3113. So both motors tested 18-20% higher than their stated KV ratings. Google searched suggested that I need to divide Castle's KV rating in half since these are both 4 pole motors, but that would provide a KV rating that is even further from what they should be.

Is this normal or should I be concerned about the difference in KV ratings? Is the Castle motor test even reliable? The only results I can find on Google for this are from 5+ years ago, so I'm not sure what to think of this.

Any help or input is appreciated.

Re: KV Rating Accuracy
 

Some variation is to be expected, since the rotor magnets - the most significant cause of part-to-part variation - often have a specified field strength tolerance in the neighborhood of +/- 10%.

20% deviation from spec is much higher than I would expect for a motor of decent quality, however, and the fact that both motors varied so much and in the same direction makes me suspect that the Castle test is not accurate. There are a few ways in which this test may result in an inaccurate measurement, and ultimate the "gold standard" is still a direct measurement of back EMF peak-to-peak voltage (something that is difficult to do without an oscilloscope or specialized motor test equipment).

Personally, if it were me, I'd install the motor and enjoy it.