Sliding struts

ABCABCABCABCABCABCABCABCABCABCABCABC

c c c c

| | | |

y y y y

XYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZXYZ

Joins the two struts, which have now

moved over one unit.

Cycling through a-x, c-y and b-z produces controlled relative motion of the two struts.