The Sarrus linkage consists of four links in two identical
groups that are perpendicular to each other. All links are
of equal length, and the linkage is driven by the rocking
motion of both lower or both upper links. The advantage of
the Sarrus linkage is that it can be used to lift the structure
connecting the upper links, providing an impressive range
of movement as seen in Figure 7-19). Note that the perpendicular
links work in different directions and thus exert
stress on each other, which is why they need to be very rigid
and preferably several studs wide for the linkage to work
properly.
The disadvantage of the Sarrus linkage is that it
requires one link from one group to be moved simultaneously
with a second link from a second group. In other