L6470 BEMF calculations

rob23 · ‎2014-02-11

Posted on February 12, 2014 at 00:59

Hi,

Is there an online version of the BEMF compensation tool? I have a couple of boards from Sprakfun that are based on the L6470 but I'm having issues getting the performance out of the stepper motors that I thought I would be able to get. Maybe I'm a bit dense but looking at the BEMF formulas I'm getting numbers that are ridiculously high so I must be messing something up somewhere.

If there isn't an online version of the tool could someone possibly walk through an example of the calculations? That way I could see where I'm going wrong and be able to apply the same calculations to other motors that I have as well.

Thanks

#l6470

rob23 · ‎2014-02-12

Posted on February 12, 2014 at 14:11

As an example this is what I am currently getting as a value based on the BEMF formula:

INT_SPEED = 4 * Rm/2�?€Lm * 2^26 * ttick where ttick == 250ns

Motor specs

Rm = 1.65

Lm = 2.8

Im = 1.68

INT_SPEED = (4*1.65/(2*pi*2.8))*(2^26)*250 =

6293988307.48

Does this seem correct? Any of the other posts I've seen about INT_SPEED they seem to be using much lower numbers.

Thanks

Enrico Poli · ‎2014-02-17

Posted on February 17, 2014 at 16:34

Hi,

I think you forgot the order of magnitude of some of the parameters.

Inductance is expressed in mH and the tick time is in ns:

INT_SPEED = (4*1.65/(2*pi*2.8*10^-3))*(2^26)*250*10^-9 =

698830748

In any case you can use the attached document for the calculation of the parameters.

Best Regards

Enrico

________________

Attachments :

BEMF_compensation.xlsx : https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006HzI1&d=%2Fa%2F0X0000000bJM%2FXBYEO0lVfnTTdcR_klKHkTpFRhcgDFrEslLENaIewO4&asPdf=false