motor inductance -> max rps

Hi,

I am new in the forum, did a small search and couldn´t find anything to my problem:

I just cannot get any further regarding your guide about choosing the right stepper-motor (https://duet3d.dozuki.com/Wiki/Choosing_and_connecting_stepper_motors#Section_Inductance) in the section "Inductance":

I am currently trying to recalc your "max rev speed"-example and getting strange results: The given example INDUCTANCE: (2 * 12) / ((360 / 1,8) * pi * 4 * 1,5) = 0,006366197724 (?) and more confusing (2 * 20 * 2 * 12) / ((360 / 1,8) * pi * 4 * 1,5) = 0,2546479089 (?)

Also posted this question on the web-site as comment. What am I doing wrong?

Hope somebody will help!

dc42

There is a calculator to woroi this out at http://reprapfirmware.org/.

Wow, that was fast, thanks so much!

But to further educate myself, can you tell me why I am getting those strange results even when I pick the numbers provided on the website (double-checked)?
(I am trying to setup a calculation-sheet where those values are taken into another calculation...and that is taken into another calculation...)

dc42

Your motor inductance is 4mH not 4H.

@dc42 THANKS! ah - of course...
so I just divide that value by 1000 and should be fine (https://en.wikipedia.org/wiki/Henry_(unit))