Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

Chapter 8 Pipe Crawlers and Other Special Cases 221
Figure 8-2 Two-track horizontal
pipe crawler
VERTICAL CRAWLERS
Robotic vehicles designed to travel up vertical pipe must have some way
to push against the pipe’s walls to generate enough friction. There are
two ways to do this, reaching across the pipe to push out against the
pipe’s walls, or putting magnets in the tires or track treads. Some slippery
nonferrous pipes require a combination of pushing hard against the
walls and special tread materials or shapes. Some pipes are too soft to
withstand the forces of tires or treads and must use a system that spreads
the load out over a large area of pipe.
There is another problem to consider for tethered vertical pipe
crawlers. Going straight up a vertical pipe would at first glance seem
simple, but as the crawler travels through the pipe, it tends to corkscrew
because of slight misalignment of the locomotors or deformities on the
pipe’s surface. This corkscrewing winds up the tether, eventually twisting
and damaging it. One solution to this problem is to attach the tether
to the chassis through a rotary joint, but this introduces another degree of
freedom that is both complex and expensive. For multi-section crawlers,
a better solution is to make one of the locomotor sections steerable by a
small amount.