to grip something tightly, it would be
important to give it as little play as
possible. We placed the wheels so
close together that they were actually
in contact, and then made sure the
input gears would mesh nicely with
the output gears.
It was important to squeeze the
wheels as tightly together as possible
since the climbing mechanism was
essentially a friction drive. Since the
ribbon would have to push apart the
friction wheels, this would create the
normal force and the resulting friction
— as long as we get the ribbon
feeding through the mechanism in the
first place, that is.
With everything sorted in the
horizontal plane, all we had to do was
tighten it up. A few more brackets
allowed the climber to be attached to
our driving base. We attached the
mechanism to a shelf on top of the
driving base, so we knew the bot
wouldn’t have the best balance as it
hung from the ribbon. Fine-tuning the
balance could be addressed once we
determined if we were on the right
track with our climbing mechanism.
For our initial test, we just wanted
to see if the robot would devour a
mock tether like a well-trained Hungry
Hungry Hippo. We could think of no
better treat for a ribbon climber than
an actual ribbon, so we selected a
velvety blue variety that promised a
fair amount of friction. We doubled
up on the thickness of the ribbon to
give the bot more to grab onto and to
increase the friction.
The initial testing was promising.
When positioned properly in front of
the bot, the ribbon would feed
through the mechanism. The
resistance we felt when pulling back
on the ribbon when the bot was in a
sitting position suggested that the
climber had a fair bit of grip, but we
were skeptical as to whether it would
be enough to hoist the entire bot up
the ribbon. We sat the bot up so that
it was facing skyward, fed in the
ribbon, and hoped for the best. The
ribbon fed through the mechanism
like before, but instead of lifting off of
the ground the bot simply spun its
wheels. We tried lifting up the ribbon
to see if the bot would come with it,
but the ribbon slipped from the bot’s
grasp like sand through the fingers.
We were still confident the
mechanism could work and that we
would at least have a proof of
concept. All we needed was a thicker
ribbon to push more against the
SERVO 12.2013 71
A BULKIER RIBBON IS REQUIRED.
A LOW KEY
ASCENT.
BUILDING A BETTER RIBBON CLIMBER.
