while still retaining the clearance that
will allow the bot’s rear wheels to
touch the ground no matter how far
up the nose gets lifted.
The mounting for the
unpowered axle at the rear of the
bot already had very little room in
the old design, and the new rear
panel made this even worse.
Therefore, I redesigned them so that
both mounting screws would be on
one side of the axle (Figure 6). This
was only really needed at the one
side at the rear, but I modified the
chassis to use the same part at the
front, as well.
The original method of mounting
the wedge was to be a bored out
5/8" steel shaft. To save weight, I
changed the design to be a 1/2"
7075 aluminum shaft secured in
place using a cotter pin at each end
(Figure 7). The 7075 might prove to
not be strong enough; it may need
to be replaced by titanium late, if
I usually incorporate Team
Whyachi MS05 power switches in my
12 lbers, but to save space and a
little weight I'll fit a Fingertech mini
power switch (Figure 8) in a recess
in one of the main side walls. It
wouldn't work if there was a weapon
motor, but with only drive motors to
worry about it should be okay in a
One thing I had forgotten in the
original design was a way to secure
the drive motors. The gearbox
mountings alone would not be
enough because the motor cases are
made of soft steel and only attach to
the gearboxes by a couple of screws.
If the motors are unsupported, then
a sharp hit will distort the mounting
face and shear or loosen the screws;
then the drive could fail.
I added a couple of plates
(Figure 9) to stop them from moving
to the center of the bot, and I'll add
24 SERVO 02.2014
FIGURE 7. Cotter pin in rear axle.
FIGURE 8. Fingertech power switch.
FIGURE 6. New axle mounting bracket.
FIGURE 5. New rear panel.