FIGURE 4. In order to accurately drill the
tapped holes at the end of each rail, the
mating frame rail is used as a template and
a right angle clamp is used to hold it
together while it is drilled.
FIGURE 5. The holes in the end of the rail are
tapped using a bottoming spiral flute tap.
to screw the frame together. Drilling the holes that went
through the face of each rail was easy. For this, I simply used
the mill and a combination countersink/drill bit to drill the holes.
However, for the tapped holes that went into the end of each
rail, I wasn’t able to mount the rails on the mill to drill them.
To solve this, I used specialized right angle clamps and a hand
drill. Clamping the two rails together at a right angle (as shown
in Figure 4), I used the rail with the through holes in it as a
template for the holes that would go into the end of the other
rail. This worked well because it meant the holes would line up,
since it was the equivalent of drilling them at the same time.
After drilling the holes, I tapped them as shown in Figure 5.
Now that the frame had been cut to size and the holes
drilled, I could pocket the frame rails. Pocketing involves
using the mill to remove material so that it retains much
of its strength but reduces weight. In our CAD model, I
preplanned all of the pocketing so that the robot would be
underweight. Using a scribe and a ruler, I marked where all
the pockets would be and then used the mill to cut them
out. Figure 6 shows some frame rails partially pocketed.
Continuing this process for every frame rail, I quickly found
myself with a completed frame, shown in Figure 7.
The next step after completing the frame was to make
the base plate. To do this in the quickest and easiest way, I
used the method talked about in the previous article. I bought
some .063” thick Lexan and cut it to the appropriate size. I
then clamped it to the frame, and used a hand drill to drill
through the Lexan, using the pre-existing holes in the frame
as a guide. Figure 8 shows the completed frame with the Lexan
attached to the bottom. Next, I used the Lexan template to
create the 1/8” 7075 aluminum base plate. This worked
very well and resulted
in every hole lining up as expected.
The finished frame and base plate
are shown in Figure 9.
Overall Assembly
FIGURE 6. The nearly
finished frame
rails are partially
pocketed for
weight reduction.
The next step after finishing the construction of the
frame was to start assembling the robot. To do this, I
began by installing the weapon motors and gearbox. I then
installed the bearing blocks for the weapon shaft assembly
and placed the drive motors in place to verify they would fit
as expected. All of this can be seen in Figure 10. Happy
with the fit of everything, I now cut the holes for the
wheels to pass through on the base plate and drilled the
mounting holes for everything that would attach to it. To
cut and drill these holes, I again used my Lexan template to
ensure everything would line up. I reattached the frame to
the base plate and mounted all of the components. I put
together the weapon assembly which included two custom
designed aluminum pulleys. With this assembled, I began
the wiring of the robot. All of this progress can be seen in
Figure 11. I also cut out the top armor out of 3/16” Lexan
and drilled those holes in it using the same template
method, except the “template” was the final product.
Wiring
The next step was to finish wiring the robot. I used
both 12 and 10 gauge wire, depending on the system. For
the weapon system, I used 10 gauge wire because of the
FIGURE 7. The completed frame is
assembled for the first time.
FIGURE 8. Thin Lexan is used to create a
base plate template.
FIGURE 9. The completed base plate is
attached to the frame for the first time.
SERVO 06.2008 39
