In the early Transformers episode "Fire in the Sky" Optimius Prime's Trailer makes its first appearance of actually getting involved in the action. After a dramatic slide, the ramp opens on the back of the trailer and out rolls this thing! As far as I know, nothing like this ever appears again in any continuity. It's a quirk of the very early days of the hasty animation being done for the show.
This model is my interpretation of that design. I designed this with my home FDM printer in mind, and indeed that is how I made mine. The barrels are quite small, so I elected to make them from a combination of brass tubing and brass rod, soldered together. The hingepin and curved washer keep tension in the pivot joint so that it stays in any given position. I printed the wheels with black filament, then printed the rest in grey and painted to get my desired colors. In order to minimize the cost of the printing through shapeways, I've put all the parts together on a sprue. If you want black wheels without painting them, then I'd order this item in black. If you are comfortable painting the wheels, the order this in whatever color you want.
There are a few items required to complete the build:
McMaster Carr Part numbers to Complete Build
90145A419 hinge pin
9716K31 curved washer
92470A028 No. 0 sheetmetal screw, 7/16 lg.
92470A25 No. 0 sheetmetal screw, 5/16 lg.
K&S Metals Part Numbers to Complete Build
#5162 1/16 Brass Rod
#5126 3/32 Brass Tube