projects where the easy PWM control of a servo
would be ideal, but where large forces would wreak
havoc on the weaklings. In those instances, we’ve
either gone with a very robust (and very expensive)
servo, or we’ve had to redesign our mechanism to
use something like a DC motor.
If only there was a way to protect a standard
servo from large forces such as heavy lateral
loading, our lives would be much easier. We’re sure
yours would be, too.
That’s where the ServoBlocks come in. They are
a simple and robust solution that will seemingly give
your standard run-of-the-mill servo superpowers. At
first, they simply appear to be aluminum frames that
envelope your standard servo.
They look strong enough, but it’s hard to tell
how effective they might be from a static picture.
Fortunately, the ServoCity website features an
attention-grabbing video where the capabilities of the
ServoBlocks are demonstrated using two paint cans.
A paint can is hung from the end of a long arm
attached to a standard servo. As you might expect,
the lateral load of the paint can snaps the horn off the
servo in a display of robotic gore apropos of a Viking
execution. The violent spectacle is repeated, but this
time the servo is equipped with a ServoBlock. Instead
of another beheading, a miracle occurs. The servo
The lever arm bows under the force of the paint
can, but that is all. A second paint can is added, and
still the servo survives. Perhaps the most shocking feat
of all comes next: Even under the weight of two
hanging paint cans, the servo can still rotate the arm
and swing the paint cans around like an axe-swinging
berserker in battle. What sorcery was this?
It was our favorite type of sorcery: physics. The
ServoBlock is a 6061-T6 aluminum frame that acts as an
exoskeleton to isolate the servo spline from the forces that
seek to do it harm.
An aluminum hub attaches to the servo spline through
a bearing, with the bearing and frame taking the force
instead of the vulnerable spline. So, was this sorcery as
easy to implement as it looked? The ServoCity paint can
video inspired us to put some ServoBlocks to the test.
A Walk Around the ServoBlock
The ServoCity website is — as usual — a Vikings’
plunder of resources that made it easy to pick out the
right items. The ServoBlocks come in a variety of flavors,
including sizes for standard and large servos, and for two
different outputs: a hub or a plain shaft. There are 24-
tooth and 25-tooth hub designs depending on the spline
of your servo.
The page on the ServoBlocks details all the key
specifications of the units, including technical drawings
with their dimensions and even a STEP file for those that
want to include the ServoBlocks in their 3D CAD models.
We have a lot of servos strewn about Robot Central
that have accumulated over the years of Twin Tweaking
and other roboting, but many of them are modified to
varying degrees (and varying degrees of success).
We wanted some fresh servos to equip with the
ServoBlocks, and ServoCity made it easy to find a 24-tooth
spline continuous rotation servo (the Hitec HSR-2645CRH)
and a standard partial rotation servo (the Hitec HS-
These servos will run you about $25-$30, which is way
less than the premium metal encased servos capable of
handling large forces without the benefit of an
exoskeleton that often run well over $100. The
ServoBlocks themselves clock in at about $27, so if they
really do allow a standard servo to handle forces that
would cripple all but the most expensive premium servo,
SERVO 01.2018 55
YOU VERSUS THE SERVO SHE TOLD YOU NOT TO WORRY ABOUT.