Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

230 Chapter 9 Comparing Locomotion Methods
relatively low top speeds of battery powered robots, forward momentum
is not included as a comparison of mobility methods in this book.
One last interesting criteria that bears mentioning is the vehicle’s
shape. This may not seem to have much bearing on mobility, and indeed
in most situations it does not. However, for environments that are
crowded with obstacles that cannot be driven over, where getting around
things is the only way to proceed, a round or rounded shape is easier to
maneuver. The round shape allows the vehicle to turn in place even if it
is against a tree trunk or a wall. This ability does not exist for vehicles
that are nonround. The nonround shaped vehicle can get quite inextricably
stuck in a blind alley in which it tries to turn around. For most outdoor
environments, simply rounding the corners somewhat is enough to
aid mobility. In some environments (very dense forests or inside buildings)
a fully round shape will be advantageous.
Size
Overall length and height of the mobility system directly affect a vehicle’s
ability to negotiate an obstacle, but width has little affect, so size is, at
least, mostly length and height. The product of the overall length and
height, the elevation area, seems to give a good estimate of this part of its
size, but there needs to be more information about the system to accurately
compare it to others. The third dimension, width, seems to be an important
characteristic of size because a narrower vehicle can potentially fit through
smaller openings or turn around in a narrower alley. It is, however, the
turning width of the mobility system that is a better parameter to compare.
For some obstacles, just being taller is enough to negotiate them. For
other obstacles, being longer works. A simple way to compare these two
parameters together would be helpful. A length/height ratio or elevation
area would be useful since it reduces the two parameters down to one.
The length/height ratio gives an at-a-glance idea of how suited a system
is to negotiating an environment that is mostly bumps and steps or one
that is mostly tunnels and low passageways.
Width has little effect on getting over or under obstacles, but it does
affect turning radius. It is mostly independent of the other size parameters,
since the width can be expanded to increase the usable volume of
the robot without affecting the robot’s ability to get over or under obstacles.
Since turning in place is the more critical mobility trait related to
width, the right dimension to use is the diagonal length of the system.
This is set by the expected minimum required turning width as determined
by environmental constraints. It may, however, be necessary to
make the robot wider for other reasons, like simply adding volume to the