34 SERVO 09.2015
slightly lighter and more compact
than the standard wiring, but much
more work.
Servo and Battery
Upgrade
Using the XQ Power 11V servo
instead of the stock HXT servo gives
me more torque on the arm, but less
speed. More importantly, it allows me
to run the whole robot using a 11.1V
LiPo battery instead of 9V disposables
(without the addition of a regulator).
This gives my drive a theoretical speed
increase of about 22%. Also, the
11.1V LiPo battery holds more power
and weighs less.
Servo Shock
Mounting
The Viper lift kit instructions
specify mounting the servo directly to
the mounting bracket with #4-40s. I
have been using servo lifter weapons in
Ant and Beetleweight robots for many
years, and my experience has been
hard-mounting the servos increases the
likelihood of the mounting ears
(flanges) on the servo case breaking
under the severe shock loads that are
common in the combat arena.
I prefer to use the rubber
grommets and brass eyelets included
with most servos to help reduce the
shock load on the mounting ears. The
grommets fit into the mounting ears
and protect them from vibration and
shock. The eyelets press into the
grommets and prevent over-tightening
of the mounting screw.
The eyelets included with most
servos are designed for 2. 5 mm
screws which are slightly larger than
#4-40 screws which the Finger Tech
servo mounts are designed for. In
order to use them, I had to drill out
the #4-40 threads on the servo
mounting bracket, then use four M2.5
x 0.45 x 20 mm LG screws and
matching nuts to secure the servo to
the brackets. This also shifted the
position of the servo slightly, causing
the arm to not line up with the slot in
the top plate. I had to cut away a little
material in order for the arm to work
properly.
Arm Pivot
Step 1 in the lift kit instructions
states: "Attach the Mini Nutstrip
pieces [to lifter arms] using two 6-32 x
1/2 screws with threadlock liquid
applied to the threads. Leave just
loose enough that they spin freely."
This is a quick and dirty way to
create a pivot axis. The threadlock
liquid (similar to super glue) will keep
the screw in place, but would make
quick repairs in the pits difficult. This
also means the polycarbonate arms
are rotating on a threaded shaft
which could dig into the plastic and
cause the arm to not operate
smoothly.
Instead, I used a pair of partially
threaded socket head cap screws. The
non-threaded portion of the screws
created a smooth bearing surface for
the arms to rotate around, and
Upgraded pivot axes.
Finger Tech Robotics Combat Viper
lifter kit.
Servo, mounting grommets,
and eyelets.
Lifter kit complete with pivot
screws trimed.
Servo with grommets and eyelets installed.
Cutting off excess motor shaft
with Dremel.