On Wed, Dec 19, 2012 at 2:41 AM, wrote: > Would it be enough to have an un-energised electromagnet, and short the > ends of the winding together, so the induced current causes a back > electromagnetic field? Probably work better with pole pieces on both item= s > designed to form a more complete magnetic circuit than a disc magnet. What you are about to invent here is a damper that works on eddy currents. A strong magnet moving in close proximity across a metal plate induces a field in the plate that opposes the motion. No power supply required, and fully automatic--the faster the magnet moves, the more opposing force. You can demonstrate this yourself with a supermagnet and an aluminum plate. For a thoroughly outrageous example, locate "The Strongest Magnet In The World" on YouTube, skip to 6:30, and watch the show. Or use this link: bit.ly/XjCPlr --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .