that might sneak in
underneath (as shown in
the right side of Figure 2,
just before The Judge was
launched by Ziggy). To avoid
that, it is a good idea to
move the center of mass of
the hammerbot forward.
The right portion of
Figure 2 shows that the
tilting angle of the chassis
is increased even more
after the hit, due to the
reaction impulse from the
impact. The speeds after
the impact and all the
involved impact energies
can be calculated from the very
same equations used for spinners.
Since the attacked robot is
hammered against the arena floor, it
usually does not move its center of
mass, it only deforms due to the
attack. This impact problem is
similar to an offset bar spinner
hitting a flexible but very heavy wall
as shown in Figure 3.
The attacked robot would then
have an infinite effective mass (not
exactly infinite, but that of the
Planet Earth!), while the
FIGURE 3. A spinner is
basically a sideways
HammerBot.
hammerbot’s effective mass would
work like an offset spinner. The
speed of the attacked robot after
the hammering is, of course, zero.
The hammerbot chassis gains
vertical speed and may, in fact, spin
backwards.
Note that if the back wheels of
the hammerbot are still in contact
with the ground immediately after
the impact against the opponent,
then a second impact will probably
occur. With the back wheels gaining
a downward speed after the initial
impulse, they will press
against the arena floor
and receive a vertical
reaction impulse. This back
wheel impulse is good for
the hammerbot, because
it prevents its chassis from
tilting backwards too
much. The final linear and
angular speeds of the
hammerbot chassis can
be calculated using the
same equations from the
second impact that
happens when a robot is
hit by a drumbot or vertical
spinner. (These proofs are
fully developed in the Tutorial.)
Summary
In this mere 1,000 words, I’ve
managed to grossly simplify the
treatment of this subject from the
Tutorial. A longer article on
ThwackBots — a close cousin to
HammerBots — is in the offing,
which should serve to provide a
more thorough understanding of the
mechanics of this interesting and
scary weapons system. SV
BUILD REPORT:
A Reintroducti n
to Wedges
● by Thomas Kenney
In mid 2007, I began the construction of Gilbert — MH
Robotics’ first antweight. The bot
has gone through many revisions
over the years, beginning as an
inertia-labs kit with sheet metal bent
over the top to form a wedge, and
going on to become one of the
flagships of our fleet of
overpowered bricks sporting hinged
wedges. The second revision of our
hinged wedge design involved a
titanium shaft supporting
two to three blocks of
UHMW or aluminum, to
which was secured the
wedge piece itself. This
general design suffered
from a few issues before it
was applied to more of our
bots; most of these
FIGURE 1. Our original hinged
wedge assembly, including the
shaft, 7075 aluminum plate, and
UHMW blocks.
28 SERVO 07.2010