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
words, the motion of the links needs to be mechanically synchronized.
Figure 7-20 shows one of the simplest synchronization
methods. Note that the Sarrus linkage can consist of
three or four groups as well, but two properly synchronized
groups are enough to provide stable movement of the upper
structure.
Figure 7-20: This Sarrus linkage uses mated bevel gears to synchronize links
between the two groups.