28 SERVO 08.2014
Afew months ago, I was making a batch of drums for my Saifu Ant kits when I
received an order for a wider drum
for a customer who was building his
own chassis. A standard Saifu chassis
is two inches between the chassis
sides; that allows 1.7" for the actual
drum itself. The customer wanted a
drum to fit a 3" gap, so I
simply made a standard
drum that was 1" longer
... but when I was
checking the customer’s
shipping address, I noticed
that he had also wanted it
to be a smaller diameter
as well! It didn't take too
long to produce a new
part, but I was left with the incorrect
It then struck me that since my
Saifu bot was about 3 oz
underweight, perhaps I could rebuild
it to use the wider drum and still
meet weight. I placed the wide drum
next to the chassis (Figure 1) and did
a quick weight calculation. I thought
it might be possible.
The drum on a Saifu has the
motor actually inside the drum, and
the thin wall where the motor is
means that the teeth have to be
mounted on only half of the drum.
The teeth end up only 0.7" apart, and
two teeth on the top and bottom of
the drum are lined up with each
Figure 4. Shoulder screw for axle. Figure 2. New panels.
Figure 3. New bronze bushing.
Figure 1. A wider drum.
A Wider Bite
; by Pete Smith