BUILD REP RT:
Building a Better
Beatle Beater Bar!
Part 1 – The Beater
● by Pete Smith
FIGURE 1. Beetle beater
bar CAD design.
Beaters are a popular adaptation of the conventional drumbot
design. The circular drum is replaced
with a thresher or beater bar. My
beetleweight drumbot Weta, God of
Ugly Things, was originally fitted
with a 6061 aluminum drum that
had M8 socket head screws as
teeth. This worked well enough, but
the soft 6061 (it was cheap and
easy to machine) was not up to the
task of retaining the teeth and by
the end of the event, it was
definitely worse for the wear. The
event also showed I needed a bigger
hit and a better bite.
FIGURE 2. Machine out
the center of the block.
find out it’s too heavy to be used on
Personally, I design using
Solid Works, and it includes a weight
calculator. Other CAD tools can be
used, or even pencil, paper, and a
little math will get you very close to
the finished weight.
The chosen design can be seen
in Figure 1. An aluminum block uses
needle roller bearings to revolve on a
5/16” diameter ground titanium
shaft. The teeth are M10 socket
head screws. A 30 tooth 3 mm HTD
pulley with UHMW flanges (down
from 40 tooth in the original to
increase RPM by 33%) is mounted
on one end. It is designed to work in
a bot with the axle centerline 1.5”
off the ground.
All drawings are available as a
download from SERVO through
the article link or through
www.kitbots.com under the 3 lb
beetle kit section.
The block is cut from a 2” x 1”
bar of 7075 aluminum. This
conveniently gives two of the three
required outside dimensions without
further machining. The block was
cut roughly to length using an
abrasive cut-off saw, and the ends
were machined square and to length
in my mill.
Safety Note: Milling
machines are dangerous if not
used correctly. Remove jewelry
and any loose items of clothing,
and ALWAYS wear safety glasses.
The center cut-out was marked
carefully and then machined out
30 SERVO 07.2011