Twin Tweaks ...
FINDING A SAMPLE.
72 SERVO 11.2012
claw and leave the top fixed.
After a little bit of rearranging the links, we were
relieved to see that the claw behaved in exactly the way we
wanted it to – the claw would close before the arm would
raise, and the claw would open after the arm had lowered
to the ground. A working arm and claw is a great
achievement, but it wouldn’t be much more than an idle
exercise if it remained detached from the Rover.
Our final task was to attach the claw to the Rover
somehow. The still plentiful leftover Minds-i frame bits
provided plenty of raw materials, but first we had to figure
out where to put the mechanism. To properly sample alien
rocks, we wanted the claw to be able to
reach the ground. At its present length, that
would be most easily achieved by hanging
the mechanism off of the front of the robot.
We were concerned that this might shift the
center of gravity in ways that might have
some unintended consequences.
Another option was to mount the
mechanism to the top of the Rover. It
wouldn’t compromise the Rover’s center of
gravity, but this option also had drawbacks.
First and foremost, mounting the mechanism
on top of the Rover would require us to
remove the solar panel. We really didn’t like
that idea, because the solar panel was not
only an important source of cool factor, but
also something that seemed inextricably
intertwined with the bot’s identity as a
Rover. Mounting the mechanism to the top
of the Rover would also mean that the arm
in its current state could not reach the
ground. We could always extend it, but that
would simply create an even larger
moment arm and even more work
for our hapless VEX motor.
Weighing these pros and cons,
we decided to roll the dice on a
front-end mount. The existing frame
of the Rover provided plenty of solid
mounting points, and the Minds-i
frame pieces were perfect for
securing the mechanism to the front
of the Rover. The bulky mechanism
and long arm compressed the front
shocks a bit, but on the bench the
Rover seemed to have no trouble
holding the arm off of the ground.
Whether the Rover could maintain
its posture over rough terrain,
however, would be the real test.
Rover the Explorer
We were finally ready to test the Rover, but we were
concerned that the bulky mechanism might compromise the
agility of the bot. We were extremely impressed by the
ability of the unmodified Lunar Rover to negotiate even the
TIME FOR SCIENCE!
