70 SERVO 12.2013
Team 1079’s robot from the 2006
FIRST game Aim High. Part of the
challenge of Aim High was to shoot
balls through a high-mounted target.
Team 1079 created a delightfully
effective shooter by powering two
wheels by pulley arrangements and
spacing them apart so that the foam
ball would be squeezed between the
wheels. We geared the wheels for
speed and when ushered between the
wheels by a feeder mechanism, the
balls would shoot out at speeds that
would make them hard to avoid in a
game of dodgeball. In the same way
the wheels could grip the ball to shoot
it, a similar mechanism could grip a
ribbon and climb it.
Unlike a softball shooter where
attaining a high speed for the wheels
is the goal, with a climber we were far
more interested in torque. A high
torque mechanism would allow the
climber to hoist itself up the ribbon,
and the resulting lower speed of the
wheels would also make for a more
controlled ascent.
With this design in mind, we
determined that the VEX kit would be
a suitable starting point. The kit had
the gears needed for a good ratio,
versatile and easy to use frame
components, and intuitive controls. We
also thought the VEX kit would present
a particularly nice challenge with
respect to ribbon climbing because the
parts were not exactly ideal.
With the RoboGames event,
weight was at a premium — the
maximum weight was about 2. 2
pounds, and putting a score on the
board was contingent upon not
damaging the tape ribbon. The VEX
kit — with its metal frame, bulky brain,
and weighty wheels — is not exactly
the portrait of a weight conscious bot.
The extra weight, however, would
make a good challenge because it
meant we would have to do an even
better job designing a strong climbing
mechanism.
The first order of business was to
sort out our gear ratio. For the best
torque, we would want a small input
gear (the one attached to the motor)
and a large output gear (the one
attached to the wheel). The VEX kit
has a nice assortment of gears, but
there were other limiting factors we
had to consider.
We planned on using VEX wheels
for the grippers on our climbing
mechanism because the rubber tires
would provide great friction. Since the
large output gear would be on the
same axle as the gripper wheel, the
size of the gear had to be slightly
smaller than that of the gripper
wheel. We opted to use the mid-size
green VEX wheels for our preferred
grippers because even though there is
a larger sized wheel, the mid-size
wheels were more manageable to
build a bracket around while still
allowing for a serious gear ratio. With
the wheels chosen, we went with the
gears that were the biggest possible
with that pairing.
With our climbing mechanism
beginning to take shape, we needed
to sort out what kind of base to put it
on. Many ribbon climbers at
RoboGames didn’t have any other
mechanism aside from the climber —
since the bot was only going up and
down, a driving base wasn’t really a
necessity. We thought that attaching
our climber to a driving base would
add an extra layer of challenge by
making it more difficult to balance the
bot, and push us to make a
mechanism strong enough to lift the
entire assembly. We realized that
adding the extra weight wouldn’t
align as perfectly with the goals of a
RoboGames competitor, but we liked
the idea of placing more emphasis on
the mechanism itself.
Tsiolkovsky’s Eiffel Tower
X110,000 may have been too heavy
to be mechanically feasible, but we
were confident that a driving VEX
base could make the ascent.
Clif fhanger
Now that we had the design, all
we had to do was everything. For the
climber mechanism, we used one long
frame piece as the base. Since the
entire purpose of the mechanism was
THE CLIMBER MECHANISM. SOME INITIAL TESTING.