I was inspired by the recent California mudslides to design a device that can propel itself through mud, and have a hollow interior center for componentry or humanitarian supplies. I considered design factors such as ease of manufacturing, affordability, and thrust ability.
I planned on driving the first version via a central gear, with holes for a universal Hobson's joint. This would make the crawler modular, and allow for any number of worm-like sections to be combined.
In the second version I replaced the worm gearing with regular spur gears, and I made the spirals deeper for more traction. Only then did I realize that the chiral pairs both spun in the same direction, and thus wouldn't propel the device forward. I considered a few options, such as driving half of the spirals on each side, with a torque reversing mechanism in the center, but this proved too costly and mechanically complicated
I solved this by having the spirals drive each other through spur gears. This removed the need for a central gear, and thus the ability to include an effective Hobson's joint. However, this new version uses fewer unique parts. There are only two sizes of gear, and all shafts are supported by common 0.5x0.25x1.125 bearings.
This version has a hollow interior channel for internal componentry, if desired.
The spirals are powered by a keyed shaft, and the gears are held in place with a shaft clip.
This demonstrates how the device can propel itself through low-traction muddy surfaces.
