Input: one of the bars pivoted on the base.
Length of the grey base bar and end bar: a
Length of blue bar: a
Length of green bars: 0.4a + 0.6a
Length of orange bars: 0.4a
Output: the grey end bar that translates along an approximately straight line (is kept always parallel to the base).
The gravity tends to keep the mechanism at stretching position.
See a real mechanism:
   • The first experiment with the M5T lin...  
Inventor files of this video:
http://www.mediafire.com/file/satil4j...