I went over to the construction site and took a new photo today. It's below. If you click on the image, you can download the original (with all of the EXIF metadata).
This wasn't ideal lighting conditions for photography, but I did what I could.
I also took my binoculars so I could get a close-up look, and found that the wheels actually have multiple loops of cable wrapped around them. The yellow boxes (one per wheel) seem to be motors that drive the wheels (but I'm guessing about that).
In this closeup (from another pic), you can see that the wheels are both "tipped inward" towards each other at about a 45 degree angle. You can also see the cables, though it's not completely clear how the cables run from below other than they wrap a bit onto the wheel in multiple loops.
I'll try to get better photos later.. Perhaps tomorrow I'll remember my telephoto lens. We'll crack this Challenge yet!