You need to read a book about stepper control. When you drive the stepper
at certain speeds it will resonate mechanically and this will cause it to
lose steps. The makers of floppy drivers know this and make sure that
their drivers never go at that speed. With your sinus you are almost
certain to run the gauntlet. The solution is a special mechanical brake
(dynamic and/or friction and/or viscous damper) or staying out of the
dangerous speed range, which requires some knowledge of it in the first
place. You can make some tests and find out (with slowly variable speed,
using the existing optocoupler to see if steps were lost). This will not
replace a motor data sheet but it will get you going imho.

hope this helps,

Peter

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads