Always wondered if it would work and today found a cheapy at Supercheap new for $29.
Has a travel of about 19cms.
Don't think it would work great for macro as the head moves forward about 5 cms on the way down but for anything with a depth of field greater should be fine. Wouldn't mind trying a wide angle converter up close next.
Variable speed and will take a camera up to 1400kgs. :)
Edit: Uploaded new footage with improvements. vimeo.com/2405669