Read here about tensegrity structures composed of two struts, part of a series of pages organized by strut count.
A 2 strut tensegrity is not really a true tensegrity as it lies flat, the struts touch, and it does not enclose space.
Snelson calls 2 struts the "kite frame," after the traditional two-strut frame that stretches the skin of an air flying kite.
Transforming a 2 strut non-tensegrity into a 3 strut tensegrity
To transform a 2 strut into a true tensegrity, a third strut is added. This new strut is added perpendicular to one of the tension lines. It thus replaces the single filament with four filaments. Snelson has a good description here: http://www.kennethsnelson.net/new_structure/structure17.htm
As Snelson explains, this 3 strut is not yet stable. Two more filaments are are needed to anchor the new, perpendicular strut to the farthest ends of the original 2 struts.
Is x-module one central x unit, or two perpendicular, intersecting struts?
Connelly cites Snelson's X Tensegrity as the simplest tensegrity. The X in the center can be considered as two perpendicular, intersecting struts.
The X can also be considered as a flat form of a central, nucleated compression structure. In nature, such a nucleus would spread the top to radiating struts in the perpendicular plane, thus each of the four radiating struts outlining the vertices of a tetrahedron. This is the nucleated form that Levin and Flemons use to model the human spine.
Two half circles
[Pars, Marcelo|Pars]] suggests that this "2-strut" tensegrity is probably the most simple tensegrity ever. For the record one should add that the tendons between the two ends of the same half circle can be removed, implying that the tensegrity has only 2 struts and 5 tendons.
Made by http://www.tensegriteit.nl/e-tetrahedron.html, Marcelo Pars