40
| FIRST Robots
RELIABLE,
POWERFUL,
ADAPTABLE:
ATTRIBUTES OF
STRONG DESIGN
KEEP GOOD
IDEAS AT
THE READY
Although the actual construction period for the FIRST
Robotics Competition is six weeks, teams are free to test
ideas throughout the year. Sometimes teams will use the time
between competitions to re-examine ideas that surfaced
during the previous competition season but were not imple-
mented. Progressing from an idea to a working design
sometimes just takes a bit longer than six weeks.
During the
2004 FIRST Robotics Competition season,
Team
100, from Woodside, California came up with a great
idea for a versatile propulsion system, but there was not
enough time to transform that idea into a working system.
Rather than scrap the idea, the team stored the design on the
chance they could find a use for it in a future competition. For
the 2006 FIRST Robotics Competition, the team resurrected
the stored design and converted it into a great competitive
advantage.
TEAM 100
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Driving Tomorrow’s Technology Award
|
Selecting a Drive Train
Team 100 began with a desire to build a
robot that could easily climb the ramp
and have strong defensive characteris-
tics. Other robot functions would com-
plement the drive train, so this system
was the first component designed. In
addition to the performance character-
istics, the entire mechanism had to be
simple enough that it could be built
using the limited tools and resources
available to the team.
Three different ideas were presented
for the drive system. A swerve drive
was proposed to allow omni-directional
movement, but this system was too
complex to build, given the team’s
capabilities. Also, a swerve drive sys-
tem was not ideal for the type of robot
needed for the 2006 FIRST game.
A two-speed, six-motor, six-wheel
drive propulsion system was also sug-
gested, as it would be fast and have the
power to force its way around the field.
This design was also considered to be
too sophisticated given the available
resources.
The third alternative was to build the
drive system from the material provided
in the FIRST Kit of Parts. This would be
easy to put together, but it also meant
that many other teams could be using
the same drive and there would be no
advantage gained.
The final design merged two of these
ideas. A two-speed transmission would
be combined with parts in the kit to
drive four wheels. The transmission
gearboxes would be constructed and
mounted on the kit frame. This would
create a powerful, multispeed drive
system mounted on the easy-to-
assemble frame.
The drive system called for six of the
most powerful motors supplied in the
Kit of Parts to provide a propulsion
edge over teams using a four-motor
propulsion system.
Transmissions would shift the system
into a low-speed, high-torque mode or a
high-speed, low-torque mode as
required. The high-speed mode would
be ideal when playing offense, to allow
the robot to outmaneuver other robots.
In defensive mode, the high-torque
option would provide an advantage with
a stronger ability to block opponents.
The high-torque option would also
improve the robot’s ability to climb the
ramp. Using six motors allowed for a
greater range of speeds without com-
promising the rotational torque applied
to the wheels. The concentration of
motors also created a low center of
gravity for the robot.
Custom gear boxes, combined with the kit
frame, provided Team 100 with an easy-to-build
chassis powered by a shiftable drive.
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| FIRST Robots
Six-Motor Drive: An
Evolutionary Design
The drive train on Team 100’s 2006
robot resulted from two years of tweak-
ing. The team first proposed using a
two-motor, two-speed transmission in
2004, but didn’t implement it. However,
the proposal sparked interest in a dual-
speed option that would be reliable and
advantageous. Although a shifting
mechanism presented complications to
the drive system, it was believed to be
worth the effort.
Following the
2004 FIRST
Competition season, a preliminary
version of the dual-speed drive system
was built. Though large, bulky, and
heavy, the system demonstrated relia-
bility and utility. Throughout 2005, the
team continued to fine-tune the dual-
speed transmission concept.
A second revision to the transmission
used gears cut from steel spur gear
stock. Transmission components were
upgraded to handle the high loads
placed on the system. The shifting
mechanism’s gears were heat-treated
to accommodate the forces from shift-
ing and changing direction and to pre-
vent failure.
The gearbox housing was fabricated
from a 1/4-inch (0.635 cm) -thick
aluminum plate, into which ball bear-
ings were pressed to hold the steel
drive shafts. The actual shifting mecha-
nism used a form of “dog-shifting,”
where a metal dog with protruding teeth
slid along a hexagonal shaft to mesh
into pockets that were milled into a gear
riding along the same shaft.
The second revision of the transmission was
sketched and drawn in AutoCAD. Two CIM
motors and one Fisher Price motor, coupled with
gears that were housed in an aluminum gearbox,
powered this version.
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