Street Sweeper
I'd wanted to do one of these for the longest time. Lately I've been strongly inclined to build one, the excuse being they're often seen around construction sites and repaving projects; in other words, ideal for the Men at Work diorama. A 1980s vintage Mobil model would be relatively easy to scratchbuild, since all of the surfaces are squared off and blocky.
Out of necessity, I built the animated parts, then assembled the truck around them. Since I did not have access to a real machine, I eyeballed all of the dimensions based on a couple dozen reference photos. Everything is mounted directly to the "street," which is a slab of thick black sheet styrene; I treated the surface with a coarse sandpaper drum in a high-speed drill to simulate a milled asphalt surface.
I knew that the big brush across the back would be relatively easy—a job for a pipe cleaner—so I started with the side brushes. It took a lot of experimenting with all sorts of different materials and processes until I discovered by accident that I could shape the pipe cleaner material into a respectable brush: I started by soaking the end of the pipe cleaner in CA, then pressed a length of tube down over the CA, and kept on pushing until the CA disappeared (below, top left). Then I trimmed away the excess pipe cleaner fibers with a miniature hair trimmer (below, top right). After slicing off the very end of the tubing with a Dremel cutoff disc (below, bottom left), I pressed the free end of the pipe cleaner onto a smaller piece of tubing to serve as the drive shaft (below, bottom right). It took multiple tries to achieve a satisfying brush shape.
Moving on to the main brush, I was faced with finding a means to rotate it without attaching anything to the ends of the brush, as there was no room on the model for any kind of mechanical connection. So, I made the brush free-turning—no easy feat—and rotated it with another, stiffer brush from the inside the vehicle. (The stiffer brush is one I'd originally chosen for the sweeper's main brush, but rejected as not looking right.)