in several ways. One of the
lightest solutions — adopted
by the super heavyweight The
Judge — is implemented using
a pair of opposing heavy-duty
chains (colored in red and
blue in Figure 1). When the
right port of the cylinder in the
figure is pressurized, it makes
the piston move to the left
and pull the red chain which
generates a rotary motion in
the hammer.
The hammer can have a
spring mechanism to move
back to its starting position
after an attack. The best
solution, though, is to have a
double-acting cylinder to
retract the hammer at high
speeds, with the aid of the
blue chain shown in the
photo. This allows the
hammer to get ready in less
time for the next attack. Also
— and most importantly — it
guarantees enough torque
to the hammer in both
directions to work as a
self-righting mechanism in
case the robot gets flipped upside
down.
Hammer Impact
The sample system
used for calculations is:
• 1,000 PSI system
• 4” bore cylinder with a
1.25” piston
• 8” piston stroke with
FIGURE 1. Here comes the Judge’s weapon.
Hammer Energy
No matter which mechanism
you use to generate a rotary
motion, it is not difficult to estimate
the energy and the top angular
speed of the hammer in a
pneumatic robot. If we assume no
energy loss due to friction or
pneumatic leaks, then the energy
delivered by the cylinder is
approximately equal to its operating
pressure times its internal volume. If
the hammer has much more inertia
than the cylinder
piston and the
transmission
mechanisms,
then we can say
that this energy is
entirely converted
into kinetic
energy in the
hammer.
If we place the cylinder
in the back of the robot,
using the mechanism from
Note that the robot will tend to
move backwards during the
acceleration of the hammer. Therefore,
it needs to compensate for that by
braking its wheels. The chassis will
also tend to tilt backwards from the
reaction force of the hammer
accelerating forward. Powerful
hammerbots may even see their front
wheels lift off the ground because
of that, as shown in Figure 2. You
can see The Judge tilting backwards
right before it even touches the
opponent. Excessive tilting may leave
it vulnerable to wedges or launchers
FIGURE 2. The Judge vs. Ziggy.
SERVO 07.2010 27
