Animated diagram here http://www.blpcomp.com/productinfo/solenoids.php As shown, push force will increase with travel. If you want a strong restoring force you may push against a spring. In that case the force will be cdecreased as the spring is compressed. Depending on spring characteristics you could get a range of results. Russell -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist