Walking Strandbeest - a free 3D model from Shapekit

A walking machine with eight legs, built on Theo Jansen's famous linkage. A small N20 gear motor under the deck turns the crankshaft through a 4 : 1 gear, and every leg's foot traces a flat line along the desk and lifts on the way back, so the body glides along at about 4 cm a second without bobbing. Four legs on each side, in two layers on crank pins half a turn apart, with the right side a quarter turn behind the left: at least three feet are always on the desk. The 48 leg parts are flat 3 mm plates that pivot on M3 screws, so they print fast and without supports.

Parts (each STL is already placed the right way up for printing)
- strandbeest-frame.stl: The body: two walls with the bearings for the crankshaft and the holes for the two hip axles, the deck for the battery box on top, and under the deck a channel and stop plate for the N20 motor. Print: Upside down, deck on the bed. No supports: the holes are teardrops and the windows have pointed tops.
- strandbeest-j.stl (print 8): From the crank pin to the top corner of the hip triangle. The big eye turns on the crank pin sleeve. Print: Flat, no supports.
- strandbeest-k.stl (print 8): From the crank pin down to the knee. It is bent so it swings past the hip axle. Print: Flat, no supports.
- strandbeest-hip.stl (print 8): The upper triangle of the leg. It pivots on the hip axle and carries the upper crank link and the knee link. Print: Flat, no supports.
- strandbeest-c.stl (print 8): From the hip axle to the knee, where it meets the lower crank link and the foot. Print: Flat, no supports.
- strandbeest-knee.stl (print 8): Joins the back corner of the hip triangle to the foot. Print: Flat, no supports.
- strandbeest-foot.stl (print 8): The lower triangle. Its tip is the foot that walks on the desk. Print: Flat, no supports.
- strandbeest-crank.stl (print 2): Sits on the end of the square crankshaft; its round hub turns in the wall's bearing. A hex socket holds the crank pin sleeve of the inner layer. Print: Flat face on the bed, hub up. No supports.
- strandbeest-sleeve.stl (print 4): A Ø7 mm sleeve with hex ends that key into the cranks. The crank links turn on it; an M3 screw runs through the middle. Print: Standing on one end, no supports.
- strandbeest-double.stl (print 2): Between the two layers: it holds the inner crank pin on one end and the outer crank pin, half a turn round, on the other. Print: Flat, no supports.
- strandbeest-cap.stl (print 2): Closes the outer crank pin. The nyloc nut on its M3 screw sits on top. Print: Flat face down, socket up. No supports.
- strandbeest-axle.stl: A 7 mm square shaft through both walls. It carries the gear and the two cranks, the right one a quarter turn on from the left. Print: Lying on a flat side, no supports.
- strandbeest-gear.stl: 40 teeth, module 1, with a hub that runs against the right wall. The motor's pinion drives it 4 : 1. Print: Gear face on the bed, hub up. No supports.
- strandbeest-pinion.stl: 10 teeth, pressed onto the motor's 3 mm D-shaft. Print: Flat, no supports. 0.12 mm layers make the small teeth cleaner.
- strandbeest-spacer.stl: Keeps the gear in line with the pinion: it runs from the left wall to the gear. Print: Standing on one end, no supports.
- strandbeest-tube-long.stl (print 8): 13.5 mm spacers on the hip axles, between the layers. Print: Standing on one end, no supports.
- strandbeest-tube-short.stl (print 4): 6.6 mm spacers on the hip axles: against the wall for the front legs, at the outer end for the back legs. Print: Standing on one end, no supports.

Also needed (not printed)
- An N20 gear motor, 6 V, 300 RPM, with a 3 mm D-shaft (body 12 × 10 mm, about 24 mm long). On 3 V it runs at about 150 RPM. Most N20 gearboxes have two M1.6 holes 9 mm apart in the face: two M1.6 × 4 screws hold it to the stop plate.
- A 2 × AA battery box with an on/off switch (about 58 × 32 × 16 mm), two AA batteries, and a rubber band or velcro strap to hold the box on the deck.
- M3 threaded rod: two pieces of 156 mm for the hip axles.
- M3 button-head screws (ISO 7380): 24 × M3 × 12 and 8 × M3 × 16 for the leg joints, 2 × M3 × 25 and 2 × M3 × 30 for the crank pins. Button heads matter: taller heads hit the next plate.
- 38 M3 nyloc nuts and 10 plain M3 nuts.
- Optional: a dab of hot glue on each foot tip for grip on a smooth desk, and a little dry PTFE lubricant on the joints.

Print settings: 0.4 mm nozzle, 0.20 mm layer height (0.12 mm for the pinion), 3 walls (the plates come out solid), 15% gyroid infill, PLA or PETG material.

Assembly
1. Print the parts: Print the 48 leg plates flat, the frame upside down on its deck, the crank pins and spacers standing up and the crankshaft on a flat side. Nothing needs supports. Turn on elephant's foot compensation, or scrape the bottom edges, so the plates slide past each other.
2. Fit the drive: Push the motor up into the channel under the deck, shaft through the slot, and screw its face to the stop plate. Press the pinion onto the D-shaft. Slide the crankshaft through the left wall, the spacer, the gear (teeth next to the pinion) and the right wall. Put an M3 × 25 into the head recess on the inside of each crank, then push the cranks onto the shaft ends, hubs into the bearings: the right crank a quarter turn on from the left.
3. Fit the hip axles: Push the two threaded rods through both walls, with a plain nut in the pocket outside each wall and one inside, so the same length sticks out on both sides. Tighten those four nuts per rod.
4. Build the inner layer: Slip a crank pin over the screw into the crank's socket. Then fill the four planes from the frame outwards, with the hip spacers on the axles between them. Plane 1: front upper crank link, front hip link, front knee link. Plane 2: front hip triangle, front foot, back lower crank link. Plane 3: front lower crank link, back hip triangle, back foot. Plane 4: back upper crank link, back hip link, back knee link. Join the joints with M3 screws, heads outwards, nyloc nuts on the inner side.
5. Close it and build the outer layer: Put an M3 × 30 into the head recess on the inner face of the double crank, then fit it over the crank pin and screw it to the M3 × 25 with a plain nut in its pocket. The outer layer goes on the second crank pin in the same order; the crank cap and a nyloc nut close it, and a nyloc nut goes on each end of the hip axles. Tighten every nyloc until it touches, then back it off a quarter turn: each leg must swing freely.
6. Let it walk: Strap the battery box on the deck, run the motor wires through the hole and connect them. Turn the crank by hand once to check nothing catches, then switch on. If it walks backwards, swap the two wires.

Safety: Small parts and screws: keep them away from young children. Take the batteries out when it is not walking.

License: Creative Commons Attribution-NonCommercial 4.0 (CC BY-NC 4.0)
https://creativecommons.org/licenses/by-nc/4.0/
Print it, remix it and share it, as long as you credit Shapekit and don't sell the files or the prints.
