Afinia/Up-Printable Strandbeest

pinshape

After tweaking GolanHertz's original model, I landed on an assemble-able version that's reasonably robust. My goal was to pay homage to Theo Jansen's genius and disprove cyclone's assertion that the model is unprintable. It won't walk well due to the floppiness of crankpins, but the mechanism works, and it was a great printing challenge. The end result is an excellent sculpture. See the "Instructions" tab for details. All parts have been scaled down to 90% to fit the build volume of the Up/Afinia printer. Any part not included here must be scaled from the original to be compatible with new parts. I printed all parts in ABS except wheels, which had severe warpage and splitting problems. For these, I used Colorfabb PLA from printedsolid.com, which has PHA added for flexibility and ease of printing. The biggest assembly issue with GolanHertz's original is the fit of snap-in shafts. They don't fit bushings as designed. Rather than scale shafts down or enlarge holes in STLs, I drilled out bushings with a 4.3mm bit. This has the side benefit of ensuring that holes are smooth and round. Even after enlarging bushings, snap-in shafts still don't work because when compressed, head diameter in one direction doesn't change. To fix this, snip off sides of one snap-in head on each shaft, perpendicular to slot. Snip just enough so that you can push (it takes a bit of force) the head through bushing. If you snip too much, the snap-head won't hold well. The splined crankshafts of the original are problematic; I replaced them with hex shafts, which are stronger and use an easier-to-print hex hole in cranks. I enlarged the diameter of these hex shafts to fit main crankshaft bushings more snugly. Also, the original had only one length of crankshaft; shorter ones are needed for two ends, which I've provided. The biggest design flaw is in crankpins (snap-in "connector d" in the original design). There's no way these can be strong enough to transmit required torque without popping out if a snap-in connector is used. I changed these to a retaining-ring style and increased their diameter to 5mm for added strength. It now holds together, but they still flex too much for real walking action unless you carefully drive both ends of the crankshaft. To accommodate the larger crankpin, I enlarged holes in wheels, but I didn't bother to revise STLs of linkages that they pass through. You need to drill out each bushing through which crankpins pass. This means one end of each dogleg linkage and also one end of each longskinny linkage. Use a 5mm drill bit. The two very long shafts that run the length of machine in lower frame bushings are obviously not printable on an Afinia, so I made smaller shafts (one per crank section) called "elbow shafts". These are a snug but movable fit inside frame bushings and can be installed one at a time while putting thing together. The main frame was sectioned to fit in printer's build volume. The sections are held together by "frame pegs". After drilling shaft bushings to 4.3mm, glue the frame pieces together with pegs while using "elbow shafts" to temporarily align sections. There is no really easy way to assemble this Thing. I think the easiest might be with the frame upside-down as shown in one of photos. Assemble all linkages, triangles, and feet to the frame before installing cranks (wheels) and crankshafts, which go in last. IMPORTANT: many/most linkages are NOT symmetrical - they have to go in a specific orientation. The thing to remember is that in every case where a snap-in shaft is used, the head of the snap-in MUST fit into a "counterbored" recess in part. If you install a linkage backwards so that the head rests against a flush surface instead of a recess, the length will be wrong and it won't snap in or hold.