> you shake the windings apart as the mass is low enough to > physically oscillate at the drive frequency You might wonder what that does to the wire coating as it gets older and perhaps a little brittle, or any potting or sealing compound I think I'd be right in saying that vibration is wasted energy. Maybe include a trimmer to tune the PWM frequency out of resonance with the load Joe ----- No virus found in this message. Checked by AVG - www.avg.com Version: 2015.0.5577 / Virus Database: 4257/8857 - Release Date: 01/02/15 --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .