Inchworm Crawler – Crank-Driven Walker (Blockineer)

Watch the video: https://youtu.be/9Osyx_4t8Ig

From the video: Blockineer #02 "The Flying Machine" (youtube.com/@blockineer). In Minecraft, eight blocks fly forever: a piston pushes the front half, a sticky piston pulls the back half after it. In the real world, the back half would be pushed backwards just as hard (Newton's third law). The centre of mass would never move and the machine would only twitch in place.

This printable crawler is the honest version. The mechanism is the same (push, clamp, pull, clamp), but the feet hold on to the table. Turn the crank and it inches forward. Lift it up, turn the crank, and it just twitches, exactly like the video says.

Parts to buy

No bearings and no metal shaft are needed. The crank shaft is printed.

Print settings

Filament (solid estimate): about 40 g PLA and 6 g TPU. Less with normal infill. No TPU? Glue angled strips of a rubber band or a thin rubber sheet under the feet instead. They have to lean backwards, so that they slide forward easily and dig in when pushed back.

Assembly

1. Slide the front foot onto the beam from the tip. Screw the M3 × 8 into the hole at the beam tip as an end stop.

2. Push the crank shaft through the first bearing post, slide the eccentric disc onto the D-shaft between the posts, and push the shaft through the second post. The D-fit is tight on purpose. Add a drop of glue if the disc slips.

3. Screw the connecting rod to the disc pin hole (M3 × 12 through the rod into the disc) and to the tab of the front foot (M3 × 12). The rod sits between the disc and the post. Do not overtighten, the rod must swing freely.

4. Screw an M3 × 12 into the hole at the crank arm end as a handle.

5. Glue the grip pads under the rear foot and under both legs of the front foot. Fin tips point backwards (away from the beam tip).

6. Put it on a smooth table and turn the crank.

How it works

• The eccentric (radius 6 mm) moves the front foot 12 mm back and forth on every crank turn.

• Front foot moves forward: its fins slide, the rear foot's fins dig in and hold.

• Front foot moves back: now its fins dig in and the rear foot is pulled forward.

• Lift it off the table and nothing can dig in: the two halves just shuffle against each other. That is the flying machine without the cheat.

The math

• Stroke per crank turn: 2 × 6 mm = 12 mm → about 83 turns per metre (minus slip).

• Lever: crank arm 30 mm, eccentric 6 mm → the push on the foot is up to 5 × your hand force.

• The Minecraft machine in the video: 8 blocks of 1 m, about 12 t, every stroke throws 6 t forward at 40 G and needs just over 1 MJ. Hovering would take about 9 MW (perfect rotor) or 13 MW (real rotor).

• This crawler weighs about 40 g and needs a few millijoules per step. It works because it has something to push against: the table.

Files

inchworm_crawler.scad (parametric, OpenSCAD Customizer: part, stroke ecc, fits) · rear.stl · front.stl · disc.stl · crank.stl · conrod.stl · pad_rear.stl · pad_front.stl · plate.stl · assembly.stl (preview only) · section_preview.png · parts_preview.png

Credits

Design: Blockineer – https://www.youtube.com/@blockineer "The game cheats. We do the math." Licence: CC BY-NC 4.0: free to print, remix and share with credit to Blockineer. No commercial use.