Dump Truck

This one went from an idea to a project as I developed a new construction site diorama. The goal is to pair it with the excavator so that there's always material to remove from the work site: after it fills up the dump truck, the dump truck dumps it all back into the hole from whence it came. Now, I realize that moving aggregate materials around breaks one of my tenets on animation, but I have a one-word defense: fun.

The first thing that had to be addressed with the truck kit was the fact that it was not designed to be animated—there weren't any protruding parts that could be drilled to make pivots. I had to make pivots using Gold Medal Models industrial ladders, which have holes to mount the safety cages. I cut the ladders at the points marked above to produce pivots that I then glued into #80 holes drilled in the truck frame and dump bed, below. A piece of brass wire completed the pivot. The gate was articulated the same way.

The mechanism is a linear drive powered by a rack and pinion gear set. The rack turns a bell crank, which lifts the hydraulic piston under the dump bed; limit switches prevent overtravel.

Revision

The more I watched the dump truck operate, the less satisfied I became. The problem was the gate: as the body tilted, the gate would abruptly pop open and then jiggle, which ruined the realism of the action. So I devised a fix.

First, I added a tiny eyelet (1) to the bottom corner of the gate; then I fashioned fine wire (2) that engages the eyelet and is soldered to a lever (3). The lever pivots at the base (4) and is connected to an actuating rod (5) that has a pivot (6) on the bell crank (7).

Here it is in action:

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