FIGURE 1.
Melty decoder
for tank drive
thinkers.
FIGURE 2.
Antweight
Melty B.
In that series, we looked at four
bots that tackled the difficult task of
making the whole bot a kinetic
energy weapon using this interesting
phenomenon of rotating bodies. In
a traditional “Full Body Spinner”
(FBS) — contrary to the name — the
outer shell spins, but the base
platform is a traditional “tank drive”
vehicle. In a Melty, the whole bot
spins, and by varying the drive speed
of each wheel as the bot spins, a
translational movement results.
Ilya Polyakov of Team Carnivore
is generally credited with the first
attempt at putting this technology in
the box. He says: “At the
time, I was taking
Dynamics as part of my
M.E. course work and the
vector math behind
combined translational
and rotational motion
really hit the spot. The
identical but opposite
rotational velocity vectors
combined with a single
translational vector made
sense in the tank drive
perfectly.”
Figure 1 attempts to
translate (sorry, pun alert)
this jargon into language
the mere mortal can
understand without
having the dreaded (and
aptly named) brain
meltdown.
Rich Olson of
Nothing Labs (previously
known as Team
SpamButcher) has emerged as the
new King of Melty. A while back, he
built a successful Antweight bot
using Melty Brain technology. “To
determine its relative position in
each spin,” Rich says, “Melty B
(Figure 2) uses an accelerometer to
measure the centrifugal force
created by the rotation of the bot.
The level of G force detected is then
run through a formula that
accurately determines how fast the
robot is spinning. Once the exact
spin rate is known, it’s possible to
determine where it is in the current
spin based on timing.”
The robot flashes an LED each
time it hits a point in the spin it
thinks is “forward” which appears as
a streak, indicating to the driver
which direction the robot will move
when the stick on the remote is
pushed forward. The bot has a top
speed of 1,400 RPM and can
“translate” at about 1.5 feet per
second. At top speed, forces inside
the robot can reach over 100 Gs.
FIGURE 3. Open
Melt schematic.
SERVO 06.2010 31
