Walker

Gerd sent me : this link. It's a design by Keishiro Ueki. A single leg linkage is in red, with the blue points a and d fixed.
(Play the local file)

bc + cd has to be slightly longer than ba + ad, so that point c always remains above line ad.
A central motor (green) can drive all legs with belts.

Step 1: build a single leg. The other 2 have to be in separate planes. A 4-cornered vehicle would need 12 legs.

Foam core prototype, linkages need some adjustment. Then imported into Fusion 360

Laser cut out of 1/4" HDF/masonite (BOSS 85% power speed 15mm/sec)

cut file
Watch the movie!

parts

Two major problems seen with this version:
  • The legs are driven with these timing belts and pulleys, the kind used on 3D printers and such. Turns out, if the belts are not under high tension, they will jump sprockets and the legs will go out of sync. With the materials I'm using, high tension is not trivial to achieve, and leads to added friction. ===> Therefore, switch to chains and sprocket wheels.
  • The assemblies are very floppy in the transverse direction. Hmm....
For the floppyness in the transverse direction: there is no strength in that direction from the 1/4" axels - they are only a few mm long. Here I increased the diameter of the surfaces at each hinge to 7cm.
I attached 2 small wheels in the back to turn it into a 'tricycle'. Transverse strength improved, but still too weak.
Simple wedge tensioner takes care of skipping teeth
Here I took 2 units, one the mirror of the other, and connected the feet with 2" dowels. This is completely stiff in the side-to-side direction!
Notice the four legs temporary. When the foot hits the floor, these are lifted up just a few mm, and the walker moves forward one step.

One full 'wheel' takes 3 of these, which would be too wide. The 2" rigid spacers between the feet may be overkill. Can I reduce the size of these spacers? Maybe to 0.0?

BTW, the torque required to run this configuration is 27 Newton-cm

OK, double-sided linkages are a must. I had enough components to make 2.
I added two steerable casters to the back, to make a tricycle-like configuration. Next: motors and controls.

My first foray into automation and control: from an Elegoo starter kit I took the IR controller, IR sensor sensor and a SG90 servo. I got an ESP32 board from Make, and did some MicroBlocks programming.

play →



back