If you want optimum off-road performance, it’s hard to beat tank-style tracks for their massive ground contact ability. On the other hand, what if there was a wheel that selectively reshaped the bottom into a flat surface for a similar effect? One might think such a device was something Tesla was working on for their newest experimental vehicle. In fact, the concept, called a “pedrail wheel” – or roughly "pedestrian/foot wheel" for the feet that poke out – was first conceived of in the late 1800s.
The system utilizes a clever internal mechanism to flatten and angle the protruding feet to continuously continuously create a flat section on the bottom. If you’re wondering why it’s not in common use today, James Bruton’s latest project may provide a few answers.
In the video, he 3D prints two pedrail wheel mechanisms, and hooks them up to a simple chassis with a caster on the back. A pair of motors and gearboxes drive the wheels in a tank-like differential drive setup. It's controlled by an Arduino clone along with a pair of BTS7960 motor drivers, and wireless interface is accomplished via an nRF24L01 RF receiver.
Initial testing starting at 7:30 in the video seems promising, as it’s able to traverse a flat surface without any sort of rubber pads for the feet. It’s also able to tackle small obstacles, and the central guide angles itself nicely as needed. An outdoor test, however, proves a bit more challenging, as it tends to knock loose objects around. A garden hose obstacle is especially problematic, as it tends to wrap around the leg protrusions.
While an interesting experiment, one could see this being a truly problematic device when scaled up, both from a performance and maintenance standpoint. There are even some obvious safety issues at play here, so perhaps this concept is best left to the history books!