30 SERVO 09.2015
finished, it was time for a test fit. This
check showed that the bushing on the
front support plate needed to be
shaved down to accommodate the
tolerance stack-up across the
After a few passes with an
endmill, the bushing was the proper
thickness to allow everything to spin
smoothly, and the final mechanical
assembly was able to be completed
Running the chain was a bit
difficult due to the close quarters, but
after some effort it was fully routed.
The whole assembly was then
installed and hooked up for testing.
Initial tests consisted of cycling
the weapon several times listening for
rough spots and watching for binding.
With no obvious issues, testing moved
to the street where the weapon was
cycled multiple times while driving the
bot around and flipping it over
At the completion of these tests, I
noticed that the lead screw had
shifted position. Some follow-up
testing showed that the issue resulted
from the weapon reaching a travel
limit while the motor was still getting
power. The Magnum775 continued to
try to drive the screw, and the result
was the sprocket spinning on the
threaded shaft and causing the shaft
The first part of addressing the
issue was the addition of a welded
washer to the end of the screw to
prevent the nut from being driven
past the end of the screw. This at
least allowed for further testing and
final weight reductions, while the
second part of the solution shipped.
With the screw pinned and
working as intended, all that remained
for the weapon were a few photos of
the completed system. SV
The top view of the robot
with the weapon motor
hidden below the chassis.
The Magnum775 stayed cool during
testing and appears to be well-suited
to the weapon.
Checking to see what does and does
not line up properly. The quick connect setup allows easy
weapon changes on Spanky.
A spring pin was added to positively
attach the sprocket to the screw. Adding a hard stop to the end
of the screw.
The fully assembled weapon without
the roller chain installed.
When inverted, the
weapon motor is fairly
exposed above the
robot. However, it can
quickly flip over to
minimize the chances