making a powerful flipper
and just try to create a
flipping mechanism that
could fire three times
without any human
intervention.
Another reason that
Reclipso was unable to really
toss an opponent was the
very limited gear ratio
between the mass in the
flywheel and the opponent.
The hook and strap
implementation of the
trigger meant that the rear
bar of the flywheel
attempted to rotate at the
same speed as the flywheel
itself.
This meant that the
flywheel’s momentum was
being transferred to an
opponent that weighed ten
times as much without any
reduction in between. In
fact, because the flipper
was a four bar linkage, the
effective gear ratio was
worse than 1:1.
The final result was an
inefficient momentum
transfer and very little
actual flipping.
Now that I had
identified the problems with
Reclipso, it was time to
solve them. The weapon
speed controller was simple
— all I had to do was find
one with a user
programmable low voltage
cutoff and fit it into the
robot. There were many to
choose from, and I
eventually settled on one
that could handle up to
40 amps.
Unfortunately, the speed
controller cutoff was the
only problem that could be
solved simply by replacing a
single component. The other
problems all required a complete
redesign of the weapon assembly.
The new design (Figure 1)
FIGURE 1. Completed assembly with thread.
to slide the clutch downward
until it lodged between the
flywheel and the coil drum.
This was done while the
flywheel was spinning at full
speed which caused the coil
drum to spin rapidly, as well.
I used Kevlar thread to link
the coil drum and the coil
plates that drive the rear bar
of the flipper.
Every rotation of the coil
drum reeled in more of the
thread and pulled the arm
through its stroke. The coil
plates at the back of the
robot were eight times larger
than the coil drum shaft,
providing an 8:1 gear
reduction to make more
efficient use of the
momentum in the flywheel.
Once the flipper arm
reached the end of its
stroke, the thread went tight
and everything stopped
rotating. The clutch wheel
was then pulled back and
upward by a pair of springs,
so it disengaged from the
flywheel and coil drum.
Once the clutch was
disengaged, the entire
assembly could rotate back
to its original position so it
was ready to fire again.
There were a lot more
moving parts involved in
making this design work than
there were in the simple steel
hook design, but the
potential for improved
flipping was definitely there.
In Figure 2, you can see
what the entire assembly
looked like with the weapon
extended. The flipper arm had
not yet been bent to its final
form for this picture, but you
can see the four bar linkage
including the rear hinge pin
from Figure 1 (right next to
my hand).
I added rubber stoppers to the
rear hinge pin to soften the blow
FIGURE 2. Installed extended weapon.
FIGURE 3. Broken Kevlar.
eliminated the steel hook and strap
in favor of a friction clutch. To
engage the weapon, I used a servo
SERVO 06.2013 29