Tensegrity Structure for Gravity-Defying Moss Garden

prusaprinters

<p>A tensegrity is a stable configuration of bars and cables. The bars don't touch each other and are only connected via the cables. If the cables are very thin compared to the bars, the bars seem to float in mid-air. The position and length of the bars and cables is carefully calculated to obtain a stable configuration that is surprisingly ridgid.&nbsp;</p><p>I designed a tensegrity and used it as the base structure for growing a moss garden. It is mind-boggling to look at in real life. 2D pictures just don't do it justice. Therefore, I invite you to play with the assembled model in the 3D viewer above to get a better feeling of its shape from all sides. Here is a video of the structure before planting moss on it:</p><figure class="media"><oembed url="https://youtu.be/yZb1oIoDDwQ"></oembed></figure><p>And here is a video of the finished moss garden. The moss partly obscures the tensegrity structure due to the added thickness and its lush organic nature.&nbsp;So, I'm not sure which version I like the most. The one with the moss only at the bottom is also looking pretty cool and doesn't require spraying it with rain water every day ;-).</p><figure class="media"><oembed url="https://youtu.be/u3hphxRAS9U"></oembed></figure><p>Much of the work went into computing the position and lengths of the bars and cables, and figuring out a way to 3D print and assemble it. Because I wanted to print it on a Prusa MINI, I split each bar into 2 (or even 3) parts that can be inserted into each other to obtain the full length. I added hooks to the places where the cables must be attached. As the position of these hooks is different for each bar, each bar is unique. Hence, I added removable id tags to each bar to distinguish them. These id tags also help orientate the bars during assembly, identify the hooks for connecting the cables, and determines the downward facing side during slicing. The hooks are designed and placed such that they can be printed without supports. The bottom part of the first bar is created stronger as it connects the tensegrity structure to the base and is therefore not reinforced by the cables. Hence it has to carry the whole weight of the tensegrity and the moss growing on it. This can be quite heavy, especially when the moss is soaking wet. The bottom part of this bar also contains a mechanism to adjust the length of the bottom 3 cables and tensioning them before tying them fully down.</p><h3>Print instructions</h3><p>Everything is printed in PETG for strength and flexibility reasons. The dimensions are designed to maximally use the print bed of the Prusa MINI. I printed everything with 0.2 mm layer height. The number of vertical shells (perimeter) is increased to 7 to avoid infill on most parts.</p><ol><li><strong>HexBars</strong><br>It is important that the bars are laid flat on their ID tags. The printability of certain features (e.g., hooks, wire stoppers) depends on it.<br>Support is only needed at two places because of the overhang. Hence select "For support enforcers only":&nbsp;<br>&nbsp; a) the inserts float above the print bed and have to be supported at the bottom,&nbsp;<br>&nbsp; b) right behind the inserts, the diameter of the bar increases to the full diameter of the bar. On one side of the bar this results in an overhang that has to be supported.</li><li><strong>HexBase </strong>(optional)<br>The hexbase is useful during assembly of the tensegrity. It does not require any supports.</li><li><strong>MossBase</strong><br>The moss base resembles a rectangular box of which two corners are sunk into the ground. This strange shape requires supports for the part that will touch the ground. Just enable “Support on build plate only”. Unfortunately, the support here is very difficult to remove. Be careful: don't hurt yourself while removing it!</li><li><strong>MoseBasePadding</strong><br>The moss base padding is inserted in the moss base to keep the point of gravity above the part that touches the ground. It does not require any supports.</li></ol><h3>Assembly and Planting Instructions</h3><p>The “Other files” section contains a <a href="https://media.prusaprinters.org/media/prints/64974/other_files/724128_1842ab92-e843-4380-8a5f-8ff476443aec/assembly_and_planting_manual_v1.pdf">manual</a> with detailed assembly and planting instructions.</p><h3>Maintenance</h3><p>Put your indoor moss garden in a place where it gets a lot of day light and spray it daily with rain water.</p><figure class="image image_resized" style="width:54.69%;"><img src="https://media.prusaprinters.org/media/prints/64974/rich_content/73a615c5-5f2b-4f43-b242-06b8991be652/dsc07009-1.jpg#%7B%22uuid%22%3A%2265189817-d4a2-4919-a949-9505bfae4bdd%22%2C%22w%22%3A1280%2C%22h%22%3A960%7D"></figure><h5>Updates</h5><p>2021.05.03 Added more clearance to the Reinforcement Rings.</p>