Six Sticks Tensegrity
An example of a perfectly rigid 3d framework containing no triangles ! Consisting of 6 sticks arrainged in 3 parallel, mutually orthogonal pairs. Each end of each stick has 2 strings attached.
The strings form 8 3-pointed stars, the centers of which form the corners of a cube.
If you want an interesting suprise, calculate the dimensions of the strings relative to that of the struts, and the distance between the struts; then for an even greater suprise, imagine that twice the amount of string is used, and instead of 3-pointed stars, triangles of string are used. ( you get a fully collapsible structure that lays itself out in a very interesting pattern.