Parametric strandbeest in OpenSCAD

This is a customizable strandbeest designed completely from scratch in OpenSCAD, using only the strandbeest linkage lengths as a guide.

There are a number of strandbeesten available on Thingiverse, but I perceived problems in all of them, such as: requiring support structure to print, asymmetrical joints, designs that haven't proven to be printable, too flimsy, too blocky-looking, or providing just STL files without CAD files for customization. So I set out to design my own strandbeest without these deficiencies. My requirements were:

• Designed completely in OpenSCAD
• No asymmetrical joints
• All extrusion profiles use graceful curves, no straight lines
• The widest leg segment (which I call a "bone", specifically bone "c" in the diagram) connects the central frame to the foot, for better stability
• All parts are printable without support
• All parts snap together, no glue or fasteners needed

That last requirement turned out to be problematic but surmountable; read my article linked next to understand why.

Printing and assembly

For information about printing, parts preparation, and step-by-step assembly, see my detailed article about this project.

Note that there is one STL file that should be printed in PETG: strandbeest_PETGparts.stl. Everything else can be PLA. I printed my strandbeest with 100% PLA, but if I do it again I would use PETG for all parts that have snap fittings. PLA is just too brittle; that's why I split out all the parts with snap fittings into one file to be printed with PETG.

Print Settings

Printer Brand: Prusa

Printer:  I3 MK3S

Supports: No

Resolution: 0.4mm nozzle, 0.2mm layers

Infill: 15% gyroid

Filament: Prusament PLA, Generic PLA, Prusament PETG for any snap-lock parts

Notes:

I managed to print the pictured strandbeest using 100% PLA but I don't recommend PLA for the parts that have locking shafts. Use PETG. For the locking shafts, I used Prusament silver PLA, which has good adhesion, but other PLA I tried (particularly the purple and gold "silk" colors shown) have terrible adhesion for snap clips, causing them to break. To be safe, print these parts in PETG. For the rest, PLA is fine. See https://www.nablu.com/2020/05/building-strandbeest.html for more explanation about why PLA is a problem for some parts.

Post-Printing

See https://www.nablu.com/2020/05/building-strandbeest.html for step-by-step assembly instructions.

How I Designed This

I designed this entirely in OpenSCAD. The curved profiles of all the bones use cubic Bezier curves. The OpenSCAD file can render the full model at any crankshaft rotation, and it can be animated also. Unfortunately I developed that only after a lot of trial-and-error printing to find places were parts interfered so I could figure out the clearances needed.

Category: Mechanical Toys