other. This reduces the "bite" as well,
since the drum only has to turn 180°
before the tooth hits its opponent ...
and often "scratches" rather than
getting a good bite.
The longer drum allowed the
tooth spacing to be increased to
1.7", and also allowed the teeth to be
staggered so they can get the bigger
A few minutes on Solid Works,
and I had the new panels designed
that would be required to widen the
bot. The dxf files were sent off to my
favorite watercut company, Team
who made me a set in 0.030" 7075
aluminum (Figure 2).
I took advantage of this rebuild
to include a stronger method of
mounting the non-motor end of the
drum. First step was to fit a larger
bushing with a 1/4" bore to the
chassis wall (Figure 3). I would have
liked to use a lighter Acetal plastic
bearing as these had previously
worked well, but I could only get a
PTFE impregnated bronze bushing at
the time I ordered the parts.
I used a 1/4" diameter by 1" long
shoulder screw (Figure 4) as the axle.
The ground surface works well with
the plain bearing — especially with a
drop of light oil — and the thicker
axle should not bend as easily in
I've had some problems with the
drive gearmotors on Saifu. The
standard eBay sourced motors had
quality issues with the gearboxes, and
using gearboxes from Finger Tech
Silversparks did not provide a full
answer as they too had their own
I checked a batch of the eBay
motors and found that some run
smoothly in forward and reverse,
whilst a few would feel rough and
sometimes would even jam if the
direction of rotation was changed
I chose a set of the smooth ones
and ran them in in both directions
(Figure 5) for some time to check
that they were reasonably reliable.
New wrap-around armor was
made from a strip of UHMW from
Figure 7. TinyESCs.
SERVO 08.2014 29
Figure 5. Running the new motors. Figure 6. New armor.