Weta, god of ugly things — my 3 lb Beetleweight — has always had a different
beater bar than the kit bots for which
it was the prototype. The beaters on
the kits are much easier to make and
are very effective, but the one on
Weta had two heavier hardened steel
bars as teeth (Figure 1). That extra
mass of the teeth meant that if Weta
met one of its clones in a fight, Weta
would usually win.
As the equation Er = ½Iw2 shows,
Rotational Kinetic Energy (Er)
increases as the “Moment of Inertia”
(I) of the object increases. To put it
simply, a heavier tooth mounted the
same distance out from the axle will
have more energy at a given RPM of
the beater than a lighter tooth will.
Angular velocity (w) is measured in
radians per second but is easily
converted into the more familiar revs
per minute (one radian per second is
equal to about 9. 55 RPM).
The problem for Weta was that
the heavier teeth meant I was very
limited on what weapon motors I
could use and still meet the weight
limits. I had been using a 3,900 kV,
28 mm diameter x 35 mm long in-runner with a one eighth inch shaft.
The main problem was that the
thin shaft would sometimes snap after
a big hit, and I lost more than one
fight as result. There was a range of
28 mm x 45 mm in-runners with 4
mm shafts which would reduce this
problem but they simply were too
heavy for my bot. I have used them
Featured
This Month:
18 BUILD REPORT: The Weta Equation
by Pete Smith
21 CARTOON
22 EVENT REPORT: Clash of the Bots 2014
by Michael Jeffries
26 EVENT REPORT: Bot Blast
by Ryan Zimmerman
The Weta Equation
; by Pete Smith
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_CombatZone.
18 SERVO 10.2014
BUILD REPORT:
Figure 1. Original beater bar.
