"Marblevator, Caterpillars" is my latest Marblevator design. The model was 3D printed using three material types: PLA, PVA and TPU.

The "caterpillars" in this model are four section ball bearing carriers containing four 8mm ball bearings. The carrier is 3D printed in PLA on a PVA raft using PVA supports. PVA is a water soluble material so when 3D printing is completed, I simply drop the caterpillar in warm water and allow time for the PVA raft and supports to dissolve.

The belt in this model is 3D printed in TPU on a TPU raft. There are eight pockets on the belt designed to hold eight 6 by 1.5mm neodymium magnets. The magnets are spaced such that the belt will pick up the caterpillars from the end of the track and transport them upward to the start of the track. Small paddles at the end of each magnet group assist in transferring the caterpillar to the track.

The remaining components of the model were 3D printed in PLA.

It's not the most reliable Marvblevator I've designed, but it does intrigue the grandkids so I like it!

As usual I probably forgot a file or two or who knows what else, so if you have any questions, please do not hesitate to comment as I do make plenty of mistakes.

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

Supplies

Soldering iron and solder.

Thick cyanoacrylate glue.

Step 1: Parts.

I acquired the following parts:

One N20 style 30RPM 6VDC gear motor.
One 5VDC 500ma power supply.
Eight 6mm by 1.5mm neodymium magnets.
Eight 8mm ball bearings.

I 3D printed the following parts at .15mm layer height, 20% infill in PLA unless otherwise noted:

One "Axle, Sprocket, Idler.stl".
One "Base.stl".
One "Belt, Dual.stl" in TPU on a TPU raft.
Four "Bolt (8 by 1.25 by 6).stl".
Two "Caterpillar.stl", printed in PLA on a PVA raft using PVA supports.
Two "Leg.stl".
One "Sprocket, Idler.stl".
One "Sprocket, Motor.stl".
One "Track.stl".
One "TrackEnd.stl".

This model is a 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 I used a tap and die (8mm by 1.25) if required for thread cleaning.

Step 2: Track Assembly.

To assemble the track, I carefully glued "TrackEnd.stl" to the end of "Track.stl".

Step 3: Belt Assembly.

To assemble the belt, I glued the eight neodymium magnets in the eight magnet pockets in "Belt, Dual.stl" making certain to use the same magnetic polarity.

Step 4: Caterpillar Assembly.

To assemble the caterpillar I pressed four ball bearings into each of the two "Caterpillar.stl" (a rubber mallet may assist in this process). The ball bearings must rotate freely in the caterpillar frame and the caterpillar frame must pivot and translate with ease.

Step 5: Final Assembly.

For final assembly, I performed the following steps:

Soldered the power supply wires to the motor terminals.
Pressed the motor into "Base.stl".
Pressed "Sprocket, Motor.stl" onto the motor shaft.
Positioned the belt assembly around the motor sprocket.
Placed "Sprocket, Idler.stl" into the belt assembly.
Attached "Sprocket, Idler.stl" to the base assembly using "Axle, Sprocket, Idler.stl".
Pressed both "Feet.stl" into the base assembly.
Attached the track assembly to the base assembly using four "Bolt (8 by 1.25 by 6).stl".

With final assembly complete, I applied power to the motor and made certain the belt rotated clockwise when viewed from the front of the model.

Next I secured the model to a firm, flat, level surface, attached one caterpillar to the belt, applied power to the model, and off it went! And for more fun, I attached the second caterpillar to the belt!

And that is how I 3D printed and assembled "Marblevator, Caterpillars".

I hope you enjoyed it!