6.270
spring 2002
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team 51 ><
chaitra chandrasekhar || anita hegde || pallavi naresh
blooper
Our Strategy was very simple: collect only one
ball, deposit it in our opponent’s tube, and then block both our opponent’s
hole and our own hole. We rationalized
that it was improbable that our opponent could score more than two balls by the
time we scored our one ball and blocked the holes. Thus if our opponent scored
one ball, we would win, and if our opponent could score two balls, we would
both win.
The Development was not so simple. Our robot needed to be fast to beat our
opponent and small to maneuver around the table and into the platform between
the two troughs. We decided to make a
25:1 gear ratio. In order to make sure
our robot had enough power we put two motors on each wheel. We had to play round a lot with the gears
and the motors in order to make our gearbox small. Eventually we made it work.
Originally, we tried to design a driving mechanism with two wheels
steering and two wheels synchro. This
made our robot too big, and so we decided to make the robot have two wheels
steering and two slip wheels. This worked well.* Our wheels slipped
properly. After we build a good driving
mechanism, we built our two baby bots. In order to tether our baby bots to our
main robot we cut the baseplate into long strips and using the soldering iron,
made holes on each end and put connectors in them to attach the strips
together. The fumes from melting the
plastic with the soldering iron were incredibly irritating. They made us feel very ill for a very long
time. Once we got goggles and were more
careful about breathing in the fumes, it wasn’t so bad. We used CDS cells, leds, and bump sensors on
our robot. Our robot however, lacked
reliability, and so perhaps more sensors would have been more useful to make
our robot’s navigation more robust.
* actually nothing really worked well.
Tips for future .270ers
1.
Building : Remember that
building your robot will take much longer than you expect. Be prepared to build and rebuild his parts
[especially the gearboxes] over and over again. Don't feel bad about taking him* apart -- you'll learn a lot
every time you start over, and each time it will go faster.
2.
Calibrating your robot will be even more
time consuming than building your robot. We thought our robot had a very simple task
to accomplish. He had only to orient
himself, drop his arm mechanism, make two turns and turn the motors on the baby
bots on. Calibrating turns and making
your robot go straight are the most time consuming processes. You often will feel as if you are getting
nowhere, but don't give up hope!
3.
Sensors : Shield your
analog sensors (CDS cells) well with black heat shrink so that outside light
sources do not screw your reading
4.
Lab : Take advantage of the opportunity to work in
lab. There are many perks. You can use their tools. You can always get advice from the TAs. You can get ideas from other teams. And most of all, you can meet new and
interesting people.
5.
Wheels: if you find your
wheels are slipping, try cleaning them with sticky tape and removing the dirt
on them. We found we would calibrate
our turns, but the wheels would get so dirty, the friction would change and we
would have to recalibrate them. Also,
make sure the axle on your wheels is properly supported. If it is not, it will bend and your wheels
will be ever so crooked, which will really screw things up.
Even if you hate 6.270 now, you'll look back and
love it, so try and have more fun now.
* your robot
The Result:
After a lot of
deliberation, we finally named our robot ‘Blooper’ (this won against Pallavi’s
favorites: Robot Ron and Robot Frank).
The night before
the qualifying round, we spent it in the lab, odors and weather
notwithstanding. Starting out on Sunday at 10am we worked straight until the
next day at 1pm when Blooper had his first round. Most of the teams including
us, abandoned the main (original strategy) and just vied for getting one ball
in which would demonstrate our ability to score and hence guarantee that we
qualify (qualification was essential for going forward in the contest). Blooper
moved using shaft encoding. Now, shaft encoding is a beautiful concept in theory
but in practice it is fraught with problems. One of the main problems is the
friction on the table. This keeps varying with time and hence the calculated
values for going straight for a certain distance and for turns (calibrated left
and right) keep changing with every run. For the qualifying round, we tried him
on the table and got the exact value for each kind of turn to ensure that he
oriented himself in the right direction. At 10am (24 hours in the lab), we took
a break and came back before a little before Round 1. The (revised) strategy
for the round was to make him push one ball in. There was no plan to block
using the baby bots. In Round 1 (the qualifier), we were pitted against a
monster and although Blooper did what we wanted him to, we lost since the
monster scored a lot of points.
Round 2 was the
day after impounding. After round 1, we caught a little sleep and headed back
to lab again. What followed was another all-nighter, filled with trials on the
table trying to make Blooper go where he had to and to get the exact values for
following the strategy. We were faced by many problems on the day of
impounding. Our handyboard crashed twice and we lost a lot of time finding
people who could fix it. Then the handyboard that was loaned to us also ran
into problems.
Due to those
various reasons, Blooper was not in great shape. He leaned towards
unreliability. On the morning of Round 2, Blooper fared worse than he had done
in a long time. He was unable to move beyond a little turn. It was later when
we were taking him back that we realized the reason behind the mystery.
Apparently two of his motors ports failed at some point between bringing him
down from the lab and our turn to go on the table. This was why he was unable
to move and it also teaches an important lesson – check your robot before going
on the table J Due to double elimination, Blooper’s two
losses went against him and he had to live with the shame for the rest of his
lifetime.