planned. Of course, I still needed to add the lift and gripper
mechanisms and the spider body. I made a quick calculation
of the combined weight of the yet-to-be-added components
and loaded down the chassis with the equivalent in lead. It
was now time to test it again to confirm that all was still on
track. I pushed the throttle forward expecting it to speed
down the sidewalk once again, but was sorely disappointed!
It moved, but even a toddler could outrun it now!
It was time to return to the drawing board and attempt
to resolve the speed issue. I was so pleased with the speed
and agility of the bare platform that I didn’t want to
sacrifice it. Something had to give.
We Need More Power, Captain!
I concluded that I had a couple of options open to me.
Either add larger and more powerful motors or significantly
lighten the load. My unrealistic expectations regarding the
ability of my chosen RC platform to carry all the extra
weight proved I still had plenty to learn when working with
this new base. I now have even more respect for the
BattleBot designers that can include all that steel and
weaponry and manage to have a quick robot!
I still believed that the Scout robot was up to the task,
but I would need to greatly reduce my design in order to
control the amount of weight I expected it to carry. It was
time to scale back and cut out all the spider’s fat!
The original plan was to use one of the many spiders I
had on hand in order to save some money and speed up
the build process. The spider I chose was very large and
menacing looking, which provided the effect I was after.
However, it included some steel reinforcements which
added considerable weight. It also had a soft foam body
which would make it difficult to install around the
mechanics without interfering with their operation.
I then conducted an extensive and fruitless Internet
search to try and find a suitable replacement. When I came
up empty, I decided to try and recruit my wife to help me
construct a custom model. This turned out to be the
perfect solution to my problem!
Before we started the construction of the spider, I took
another look at my plan to use a linear servo to lift the
front of the arachnid. If I was going to go with a lighter
one, was there another option? I’ve had great success
using the servo powered gearboxes from the Actobotics line
at ServoCity for my articulated bodies. I figured it would
have the necessary torque to raise the body, now that I’d
replaced my original spider with a much lighter one. I
mounted it up, attached some weight to the lifting arm,
and gave it a test. It handled the load like a champ, with
the added bonus of requiring much less juice — allowing my
batteries to last significantly longer.
It was now time to build a framework to attach the
channel to which the gearbox and gripper would be
affixed. I started with two pieces of 12 inch channel and
cut them down until I was happy with the proportions.
These were simply connected with a hinge, giving it a very
wide range of motion. Connecting the servo horn on the
gearbox to the upper channel was easy once I had the
mounting point selected by using 6/32 threaded rod and
ball linkages. I then built a protective structure around the
servo to allow the body to be attached without interfering
with the mechanism.
The gripper kit was a snap to assemble (again, thanks
to the easy-to-follow video instructions). After only a few
minutes, it was ready to pinch away (Figures 3 and 4).
SERVO 09.2015 71
Figure 3. Head lifter and gripper mechanisms are
complete. Figure 4. Primed and painted black awaiting a body.