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AURORA uses a frame system that consists
of a continuous belt, the drive spine attached to it, and the guide
spines, which deflect to bow the belt. The guide spines retain the bent
shape to enact a turning motion.
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Pittsburgh, PA—Most tracked
mobile machines and robots use dual-treads, and change the speed of one track
relative to the other for steering. In contrast, the AURORA (Advanced Urban
RObot for Reconnaissance and Assessment) from Automatika uses a steerable,
single-tread locomotor system that relies on three enabling innovations:
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a flexible elastomeric belt for the tread
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a guide spine that holds the belt captive, and flexes to shape the tread
for steering
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and an articulating central drive spine
Departing from the theory that tracked vehicles need at least two treads to
steer provides a smaller, lighter, less expensive design, according to Hagen
Schempf, chairman and chief scientist. “Most compact dual tread units weigh 50
lbs,” he explains. “The AURORA prototype weighs only 23 lb, including the tread,
front and rear posture hubs, and a central enclosure.
Schempf notes two key design challenges: develop a controllable flex
structure to shape, guide, and retain a new type of laterally compliant, yet
longitudinally rigid flex belt; and integrate driving and steering
(articulation) in a compact package.
For the belt, a continuously cast urethane webbed-grouser belt design beat
out competing technologies such as slatted conveyor sections, and plastic
grousers with intermediate webbing because it was the most rugged, reliable, and
straightforward to manufacture, according to Schempf.
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A single tred can
steer
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A steerable track and guide
system, called the drive spine, is glued to the belt’s inside-kerf. Made of
medium durometer, urethane with embedded Kevlar backbone fibers, the
custom-molded drive spine uses a set of drive pins with low friction ends to
engage drive sprockets. “The biggest enemy is friction,” explains Schempf.
“Right now we use sliding friction, but if we scale up in size we can use
rolling elements instead.”
A pancake-style brushless motor drives a coaxial-mounted, two-stage,
planetary gearbox at the end of the assembly to move the continuous tread.
Internal clutches and brakes allow gear-ratio changes for low speed (climbing)
and high-speed (escaping) operation. Two stepping motors are used, one at each
end offset longitudinally from the cylindrical end sections, to articulate the
drive spine. Each is geared through a helical gear set, and moves each
cylindrical end-section ±30° for a net 60° steering curvature angle.
Test results indicate that the system is capable of rough terrain driving and
steering, while also climbing stairs and achieving sufficient traction and
floatation in sandy, wet, and soft soils. “It climbs 60% grade slopes, and
crawls through vegetative stands much taller than itself. A paddle deploys for
self righting and climbing onto obstacles taller than half its height,” Schempf
notes.
“The guide spines worked surprisingly well,” Schempf says, “even becoming
self cleaning due to the drive pins in the drive spine sweeping debris from the
groove. The continuous belt system’s lack of pretension afforded by the complete
capture of the belt, means you would have to destroy the belt in order to throw
it.” Future guide spine development will include careful material selection to
maximize wear and life without excessively impacting power
draw.
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