the design for the most part, while
substituting more reliable materials
to strengthen the design where
needed.
Despite the improvements,
there were still some weak points
in the Gold Sparks gearmotor,
mainly gears occasionally stripping
out and breaking due to the small
pitch, along with the output stage
breaking loose of the drive shaft.
Built to combat these issues, the
main feature of Fingertech’s
newer ‘Silver Spark’ motors are
the larger pitch of the gears
(Figure 2) compared to the Gold
Sparks, while keeping the same
basic dimensions, 11 mm mounting
pattern, and not adding more than
a few grams for the equivalent gear
ratio. In addition to all of this,
they’ve added a whole new batch
of gear ratios, ranging from half of
the lowest Gold Spark ratio to twice
its highest.
In the months leading up to
their release, Fingertech has had a
number of these motors going
through rigorous testing in the
arena. I’ve tried out a number of
the new models in some of my
recent small bots. In August ‘ 11,
I wrote a build report for SERVO
on one of these bots — an
Antweight wedge. I had been
running surplus Maxon 17:1
gearmotors for years, and with the
Maxon stock starting to dwindle,
the lower ratio Sparks now
available, and the FK-050’s ability
to run off of 18.5V without burning
up, it seemed the perfect
opportunity to switch over and
begin looking for an alternative
drive motor. There are more
details on the build itself in
the mentioned article. Overall,
the 11.1:1 Silver Sparks have
handled more abuse over a
dozen fights that it’s taken to kill
at least one Maxon motor in the
same time frame.
A few months before
building Rudy, I first tried out
the Silver Sparks in a much more
abusive testing application,
namely using them as the drive
for my three pound weaponed
robot, Misdirected Aggression. I
was stepping down from the B16
motors that were usually the
standard for a Beetle spinner’s
drive train in an attempt to put
some more weight into the armor.
I had already tested some 50:1
Gold Sparks in the application, and
they had stripped out after a few
seconds of driving around, so I
wasn’t too confident in the newer
gearmotors at first.
Despite this, the final Silver
models eventually proved their
worth, and held up fine until a
massive impact ripped the motor
from the gearhead, despite the
red-Loctited mounting screws. This
issue was eventually fixed by press-mounting the full gearmotor in a 1”
wide UHMW block (Figure 3)
similar to how I had previously
secured the B16s.
FIGURE 2. The final stage of the Silver
Spark gearbox compared to the smaller
pitch of its predecessor (left).
In addition to eliminating the
need for mounting screws to the
gearmotor’s face, this press-fit
supported the FK-050 motor,
preventing it from being removed
from the gearhead. The Silver
Sparks have worked great from
then onward, with no motor or
gearbox failures not related to the
bot’s unprotected wheels. I’d
recommend a similar mounting
method for anyone planning on
using a single pair of Silver Sparks
in anything over one pound.
To conclude, the Silver Spark
gearmotors have proven their value,
holding together in applications where
most similar small gearmotors would
have failed. The Silver Spark gearmotors
are currently available from
www.fingertechrobotics.com, and
Finger Tech’s US distributer at
www.robotmarketplace.com. SV
FIGURE 3. Supportive mounting for a 3 lb
Beetleweight's Spark drive motor.
SERVO 10.2011 37