Wacky Walker

Perhaps the most convoluted walking mechanism I've ever seen, "Wacky Walker" was a lot of fun to design, 3D print, assemble, test, and, most important, watch in action!

The inspiration for this model came from JK Brickworks Lego reproduction of a late 1980s toy known as "BearMobill" (yes, me neither).

The model incorporates a motorized chassis hanging from an oval track having free rotating legs. When the chassis passes beyond the front pair of legs, it's weight is tuned just enough to flip the oval track over bringing the previously rear legs to the front to repeat the process.

Designed using Autodesk Fusion 360, sliced using Ultimaker Cura 4.12.1, and 3D printed in PLA on Ultimaker S5s.

Soldering iron and solder.

Thick cyanoacrylate glue.

Double sided sticky taped.

I acquired the following parts:

• One N20 30RPM 6VDC gear motor.
• One four cell AAA battery pack with switch.
• Four AAA batteries.
• Four R07 O-Rings (10mm ID, 2.5mm section).
• A pack of various size neodymium magnets.

I 3D printed the following parts at .15mm layer height and 20% infill:

• Two "Axle, Gear, Bevel.stl".
• Four "Axle, Leg.stl".
• Two "Axle, Wheel.stl".
• One "Battery Case Holder.stl".
• One "Bevel, Gear, Axle.stl".
• One "Bevel, Gear, Motor.stl".
• One "Chassis.stl".
• Four "Leg.stl".
• Two "Mount, Legs.stl".
• Four "Standoff, Leg.stl".
• One "Track.stl".
• Two "Wheel.stl".

This model is a fairly high precision print and assembly using at times very small precision 3D printed parts in confined spaces with highly precise alignment. I sliced my parts using Ultimaker Cura 4.12.1 "Engineering Profile" which provides a highly accurate tolerance requiring minimal if any trimming, filing, drilling or sanding. However, prior to assembly, I still test fitted and trimmed, filed, drilled, sanded, etc. all parts as necessary for smooth movement of moving surfaces, and tight fit for non moving surfaces. Depending on your slicer, printer, printer settings and the colors you chose, more or less trimming, filing, drilling and/or sanding may be required to successfully recreate this model. I carefully filed all edges that contacted the build plate to make absolutely certain that all build plate "ooze" is removed and that all edges are smooth using small jewelers files and plenty of patience to perform this step.

The model also uses threaded assembly, so an M8 by 1.25 tap and die set would assist in thread cleaning.

To assemble the chassis, I performed the following steps:

• Pressed "Bevel, Gear, Motor.stl" onto the motor shaft.
• Pressed the motor assembly into "Chassis.stl".
• Positioned "Bevel, Gear, Axle.stl" in the chassis assembly and secured it in place with two "Axle, Gear, Bevel.stl" (a small dot of glue may assist in retaining these components).
• Inserted the four AAA batteries into the battery pack.
• Placed double sided sticky tape on the side of the battery pack opposite of the switch.
• Centered the battery back into "Battery Case Holder.stl" and secured it in place.
• Slid the battery pack holder onto the chassis assembly.
• Soldered the battery case wires to the motor such that the motor shaft rotated counter clockwise when viewed from the motor shaft end of the motor.
• Adjusted the motor position such that the motor gear aligned with the axle bevel gear.
• Applied a thin strip of double sided sticky tape to the battery case holder top rail.
• Secured the battery wires to the tape.

To assemble the track, I performed the following steps:

• Threaded two "Standoff, Leg.stl" into one "Mount, Legs.stl", then repeated the process with with the remaining leg axles and mount.
• Attached the four "Leg.stl" onto the leg mounts using four "Axle, Leg.stl", making certain the legs rotated smoothly on the axles.
• Pressed each leg assembly into "Track.stl".

For final assembly, I performed the following steps:

• Slipped two O-Rings onto each "Wheel.stl".
• Positioned the chassis assembly under the track assembly.
• Positioned one "Axle, Wheel.stl" into the chassis assembly, and secured in place with one wheel assembly (a small dot of glue may assist in retaining these components).
• Repeated the previous step with the remaining wheel axle and wheel assembly.

With assembly complete, I proceed to weight and balance the chassis. The weight of the chassis has to overcome the mechanical advantage of the track and legs behind it. In order to accomplish this, I added various neodymium magnets to the top of the battery pack which totaled 1.3 ounces (38 grams), bringing the final weight of my chassis was 5.2 ounces (149 grams) until the model operated properly. Also, the chassis must be level, so I slid the battery pack fore and aft until the chassis was level, then secured the battery pack to the chassis with small dots of cyanoacrylate glue.

And that is how I 3D printed and assembled "Whacky Walker".

I hope you enjoyed it!