brusless motor kv to rpm (using nimh battery)

[gkatz 58]

hi all
I have read that in order to convert from kv to rpm the math is 1000kv motor with a 2s (7.4v) battery will give 7400rpm.

it the math the same for nimh? so that a 7.2v nimh will provide 7200rpm (for 1000kv)?

thanks

[Twinfan 1834]

Yep!

[alvinlwh 7063]

Kv (not kV or kv) is also rpm/v. So just multiply it by your battery output to get the final rpm. In your example, it will also be 11100rpm with a 3S (11.1v) lipo or 8400rpm with a 7S (8.4v) nimh. 

[Tamiyastef 2547]

A fresh and fully charged 3S Lipo gives you 4,2V x 3 = 12,6V (and not the stated 3,7V x 3 = 11,1V) so per 1000Kv this is a difference of 1500rpm. I have no idea if a fresh and fully charged Nimh also has a higher voltage than the stated 1,2v per cell?

Probably not that important as the calculated rpm is only valid for a motor with no load...

[alvinlwh 7063]

On 8/5/2024 at 3:11 PM, Tamiyastef said:

A fresh and fully charged 3S Lipo gives you 4,2V x 3 = 12,6V (and not the stated 3,7V x 3 = 11,1V) so per 1000Kv this is a difference of 1500rpm. I have no idea if a fresh and fully charged Nimh also has a higher voltage than the stated 1,2v per cell?

I had seen a Nimh 6S hot off the charger at 9V.

[Howards 594]

Yeah, NIMH come off the charger somewhere around 8v - 9v but will approach their nominal charge v earlier than lipo.