[WayneHill]

Originally Posted by lerman Years (actually decades) ago, I saw zero backlash worm gears used in radio tuners. They consisted of two thin gears mounted on the same shaft with a spring causing them to be forced to rotate in opposite directions relative to each other (just a few degrees). They meshed with a single worm. One of the gears was screwed to the shaft. The other just applied pressure against the worm. Ken

http://www.antibacklashgear.com/