Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

There has long been a belief that tracks have inherently better mobility
than wheels and anyone intending to design a high mobility vehicle
should use tracks. While tracks can breeze through situations where
wheels would struggle, there are only a few obstacles and terrains which
would stop a six wheeled rocker bogie vehicle, but not stop a similar
sized tracked vehicle. They are
• very soft terrain: loose sand, deep mud, and soft powder snow
• obstacles of a size that can get jammed between wheels
• crevasses
They get this higher mobility at a cost of greater complexity and lower
drive efficiency, so tracks are better for these situations, but not inherently
better overall.
Tracked vehicles first started to appear in the early 1900s and were
used extensively in WWI. The basic layout used then is still in use today
on heavy construction equipment; a drive sprocket at one end, an idler
wheel at the other that usually serves as a tensioner, and something in
between to support the tracks on the ground. This basic, simple layout is
robust and easy to control. Even in its most simple form, this track layout
has all of the improvements over wheels previously listed.
The continuous surface in contact with the ground is what produces
the benefits of tracks. The long surface combined with widths similar to
wheels puts a large surface on the ground. This lowers ground pressure,
allowing traveling on softer surfaces. It also provides more area for
treads, increasing the number of teeth on the ground.
The continuous surface eliminates a wheeled vehicle’s problem of
becoming high centered between the wheels on one side. A correctly
sized obstacle can get caught between the wheels on one side, but the
track stays on top. The wheeled vehicle can get stuck in these situations,
where the track would simply roll over the obstacle.
Perhaps the most important capability the continuous surface facilitates
that a wheeled suspension cannot match (without undue complexity)
is the ability to cross crevasses. Clever suspension components can
be added to a six-wheeled or eight-wheeled vehicle to increase its nego-
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