Mechanical Rigidity/Video demo cube design
Cube design
Three different techniques are demonstrated to create a rigid frame: bracing, full panel and "picture-frame" open panel, when using extrusion (or other materials for edges) that are themselves of insufficient strength and diameter to provide full rigidity on their own. The use of straws is therefore really helpful to demonstrate the bending that can occur in long length struts (even 2020 extrusion), and the use of paper clearly helps illustrate how force on one corner of the frame transfers to a load on the panel material, through "crinkling" (and in some instances actual tearing of the paper). Of particular note, early in the video, is the importance of knowing how a single diagonal brace will act under compression, but also demonstrating that two low-cost braces (in a cross) can be extremely effective.