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:
https://www.youtube.com/watch?v=E19ht39x7hY
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