some fellow students at
Worcester Polytechnic
Institute. Figure 5 shows
the pile of parts slowly
growing and the robot
beginning to take shape.
A fellow teammate
shows how the robot will
basically look in Figure 6.
After much help and
additional work, I added
UHMW side armor for
the top frame along with
Lexan braces on the legs
to stiffen them. I mounted all of the
components except the hammer
arm and did a quick test drive to
see how the design works. Figure 7
shows Herald nearly complete!
At this point in the build
process, I spent about a week
testing different configurations in
terms of heights of the legs. I was
running into the expected problem
that the center of gravity was too
high, so the robot was tipsy front
to back. To counter this, I added a
rear wheelie bar and two spars on
the front two legs to prevent the
robot from doing face plants.
With the robot now stable, I
concentrated on the weapon
system. We completed the design
for the hammer arm, spending a
little extra time making sure it had a
unique look. To do this, we used a
CNC milling machine and cut it out
of 3/8” 7075 aluminum. A hammer
head with replaceable tips was then
FIGURE 3. A custom
shaft mount is created by
welding a two-piece shaft
collar to a steel plate.
FIGURE 2. A custom slip clutch was built
consisting of a hub and friction plate that
squeezed a sprocket using three screws
and split lock washers.
To solve this problem, I designed an
adjustable slip clutch that would go
on the driven sprocket. By using a
steel hub, a friction plate, and three
screws with split lock washers I was
FIGURE 4. A large 40 tooth, 12 pitch steel
gear was chosen to bolt onto the hammer
arm. Here it is shown after the lightening
holes and mounting holes are complete.
able to build a clutch with minimal
weight and space that captured
the sprocket between the hub and
friction plate. This can be seen in
Figure 2. A secondary stage gear
reduction then brought my maximum hammer speed down to 400
RPM as required by the rules.
The next step was to create the
mounts for the stationary shaft.
Rather than spend a lot of time
milling a shaft mount, I
decided to use two-piece
steel shaft collars welded to
steel plates as shown in
Figure 3. Next, I drilled and
tapped the holes in the large
steel gear so it could mount
to the hammer arm. I also
drilled four lightening holes,
all of which can be seen in
Figure 4.
I next made the base
plates and built the four leg
assemblies with the help of
FIGURE 5. Herald’s pile of parts
begins to come together.
FIGURE 6. Teammate
Ciaran demonstrates
how the frame pods
fit together.
24 SERVO 06.2008
