Twin Tweaks ...
FIGURE 12. A PRELIMINARY LAYOUT FOR THE NEW BRAIN.
Protobot did not escape the transplant
completely free of side effects.
The trim seemed to be fine, but
Protobot was suffering from a robotic
form of dyslexia — pressing the j
oystick forward caused the robot to
turn left, backward was right, right
was forward, and left was backward.
Rotating the radio by ninety degrees
allowed for the intuitiveness of the
directions to be restored, but having
the antenna stick out several feet to
your side did not do spectators any
favors. We tried the easy solution of
switching around the
location of the PWM
connections, but Protobot
refused to conform to
conventional joystick
directions.
This, however, brings
us to another advantage of
the brain transplant. The
Vex microcontroller can be
programmed in the
delightfully accessible Easy
C language, and switching
the directions of the motors
based on joystick input was
a snap. Back in the heyday
of Modos, the default programming
language for the FIRST bots was still
C, and the option of using Easy C
made fixing our little direction
problem as simple as the name would
suggest. One might point out that it
may seem foolish to praise the Vex
microcontroller for providing an easy
solution to the problem that it actually
caused, but we think a problem easily
solved is not much of a problem at all.
After a successful test run, we
were ready to make the brain
transplant a bit more permanent by
FIGURE 10. PROTOBOT SCHEMATIC
BEFORE THE TRANSPLANT
.
FIGURE 11. PROTOBOT SCHEMATIC
AFTER THE TRANSPLANT
.
mounting the Vex parts properly
instead of letting them precariously sit
atop the abandoned IFI controller
without any protective restraints.
Protobot’s electronics shelf was a bit
too busy to accommodate the new
components, but it was easy to make
room. In our haste to get the original
Protobot functioning, we did not
bother to remove unnecessary parts
and numerous Spike relays populated
the shelf next to the IFI controller.
Removing the relays gave us the
real estate necessary to mount the
Vex components even without
removing the IFI controller. We could
remove the IFI controller if we really
wanted to, but the shelf on Protobot
was a handy place to store it. If we
were to pursue the robotic equivalent
of appendectomy, we could remove
a lot more than the unused
microcontroller. The radio could be
removed, extra wires could be excised,
and a superfluous fuse block could be
bid a farewell. All of that was simply
replaced by the Vex microcontroller,
the receiver, and the 7.2 volt battery
pack. We were pleased by the
economy of it all.
The Spike relays happened to use
mounting holes that were the perfect
size for the Vex kit screws, but our
luck was not enough to have the
leftover holes line up perfectly with
our new components. We were still
able to make use of the holes by
fastening the Vex parts to the shelf
with tie wraps, and while they are not
the most elegant mounting solution
they are undeniably effective.
Our Vex battery, on the other
hand, used one of our other favorite
mounting solutions — Velcro. We like
Velcro so much that we had actually
used it to attach the IFI controller
backup battery to the electronics
shelf in Modos, and unlike our PWM
connections, we just so happened to
outfit both battery packs with the
same side of the Velcro. The battery
packs were even of a similar size (the
Vex pack was a bit longer), so our
Vex battery fit perfectly into the place
where the FIRST backup battery had
been. Soon we were driving Protobot
around again, and this time without
70 SERVO 05.2009
