Hasso-Plattner-Institut
  
Hasso-Plattner-Institut
Prof. Dr. Patrick Baudisch
  
 

TrussFab: Fabricating Sturdy Large-Scale Structures on Desktop 3D Printers

Robert Kovacs, Anna Seufert, Ludwig Wall, Hsiang-Ting Chen, Florian Meinel, Willi Müller, Si-jing You, Maximilian Brehm, Jonathan Striebel, Yannis Kommana, Alexander Popiak, Thomas Bläsius, and Patrick Baudisch

TrussFab is an integrated end-to-end system that allows users to fabricate large scale structures that are sturdy enough to carry human weight. TrussFab achieves the large scale by complementing 3D print with plastic bottles.

Unlike previous systems that stacked bottles as if they were “bricks”, TrussFab considers them as beams and uses them to form structurally sound node link structures based on closed triangles, also known as trusses. TrussFab embodies the required engineering knowledge, allowing non-engineers to design such structures.

While freestanding bottles tend to break easily, truss structures essentially consist of triangles. In such an arrangement, it is the structure that prevents de-formation, not the individual bottle. The main strength of trusses is that they turn lateral forces (aka bending moments) into tension and compression forces along the length of the edges (aka members). Bottles make great members: while they buckle easily when pushed from the side, they are very strong when pushed or pulled along their main axis. TrussFab affords building trusses by combining tetrahedra and octahedra into so-called tetrahedral honeycomb structures.

Walkthrough of the TrussFab system

Step 1: Automatic conversion. One way to create TrussFab structures is to convert an existing 3D model using Truss-Fab’s converter. As shown in the figure below, this converts the volume of the model into a tetrahedral honeycomb structure, allowing it to bear substantial load.

Step 2: Editing. We implemented TrussFab’s editor as an extension to the 3D modeling software SketchUp. TrussFab’s editor offers all the functionalities of the original SketchUp system, plus custom functions that help users create sturdy structures. In particular, TrussFab’s editor offers primitives that are elementary trusses (tetrahedra and octahedra), tools that create large beams in the form of trusses, and tools for tweaking the shape of structures, while maintaining their truss structure. TrussFab’s integrated structural analysis calculates the internal forces in the structure and warns users if it would brake.

Step 3: Hub generation. After designing a structure, TrussFab’s hub generator generates the 3D models of all hubs. The system genarates 3D printable hubs for spacial structures and laser-cuttable 2D hubs for facades, as shown in the figure below.

Step 4: Fabrication. Users then send the 3D model files produced by the hub generator to one or more 3D printers in order to manufacture them.

Step 5: Assembly. Users finally manually assemble their structures by following the unique IDs embossed into each hub.

We have validated our system by designing and fabricating tables and chairs, a 2.5 m bridge strong enough to carry a human, a 5 m diameter dome consisting of 512 bottles and a functional boat that seats two.

Conclusion

TrussFab is an integrated end-to-end system that allows users to fabricate large structures that are sturdy enough to carry human weight on desktop 3D printers. Unlike previous systems that built on up-cycled plastic bottles combined with 3D print, TrussFab considers bottles not as “bricks”, but as beams that form structurally sound node link structures also known as trusses, allowing users to handle the forces resulting from scale and load. TrussFab embodies the required engineering knowledge, allowing non-engineers to design such structures and allows users to validate their designs using integrated structural analysis.

 

publication:

TrussFab: Fabricating Sturdy Large-Scale Structures on Desktop 3D Printers
In Proc. CHI'17. Full Paper.