about as ungainly as the fictional monster. To Fingertech’s
credit, the chassis gave our towering, rule-noncompliant
Sumo robot solid footing, but we knew that many
improvements could be made.
That cliffhanger of sorts is where we left the Cobra
last time. The bot was functional, but it certainly wasn’t
ready to dominate the dohyo. We thought a second look
at the bot would be important for a number of reasons.
Firstly, there was the aforementioned pride in our work,
but secondly we think it is a good reflection of the design
process that roboticists engage in whether their project is
for a competition or for experimentation. Getting the
robot working is never the final step — there are always
improvements to be made — and the best competitors and
most productive experimenters are often those most
skilled at the fine art of optimization.
One Battery Pack to Rule
Our first order of business in optimizing our
transplant patient was to get the power requirements
under control. The current incarnation of our Mark III uses
two separate battery packs: a 9V cell for the board
electronics and a four pack of AA batteries for the servos.
We’ve all been there. As deadlines loom, we eschew
elegant and possibly more effective solutions for
something tried and true. This “if it isn’t broken then
don’t fix it” mentality led us to transplant the Mark III’s
battery packs along with its brain, even though those
batteries alone were not sufficient to power the mighty
Spark gearmotors on the Cobra chassis.
We had to add an extra LiPoly battery pack to give
the Spark gearmotors the voltage they hungered for, and
that led to an ungainly robot toting three battery packs.
This beast of burden certainly wasn’t compliant with mini
Sumo height or weight requirements, but we justified our
decision with that familiar refrain of the initial design:
“Well, it works!”
Now that we were taking a second look at the bot,
we were determined to cull the herd of battery packs and
use only the best pack for the job: the 11.1V lithium
polymer “Rhino” battery pack. The Rhino pack is compact
and very lightweight — perfect for a weight conscious but
power hungry bot. What discouraged us about this
battery initially is that it offered far more power than the
Mark III actually needed, and we were a bit apprehensive
about the dangers of overvoltaging.
The Mark III used a 9V cell for the board electronics
and the four AA battery pack for the drive servos. The AA
pack for the drive servos was an easy elimination, though,
because now the bot had the four Spark gearmotors
which drew power from the LiPoly pack via the Tiny ESCs.
After a quick battery-ectomy, we tested the robot and the
motors sprang to life, seemingly happy to be free of the
unnecessary batteries. This just goes to show that some
optimizations can be super simple while still vastly
MOUNTING THE LINE FOLLOWING SENSORS.
THE SRF-05 ULTRASONIC SENSOR FROM DEVANTECH.
RETRIEVING THE SOCKETS FOR THE ULTRASONIC SENSOR.
SERVO 09.2012 69