In addition to traditional hobby rotary servos,
roboticists are fortunate to have a selection of specialty
servos. Robot-specific servos have been created for the
humanoid and arm market, as well as brackets and
hardware to make complex linkages. At the high end are
Dongbu’s Herculex and Robotis Dynamixel digital servos
with amazingly high power and capability.
They have encoders, dedicated programmers, and
specialized communication protocols — all beyond the scope
of this article. Lately, some of their mechanical features are
showing up on cheaper digital “robot servos,” such as the
LD2015 shown in Figure 7.
It’s “wingless” (no mounting flanges) and has an
integral axle opposite the output shaft for increased
strength and less flexing.
Sail winch servos (720 degree servos) have different
internal gearing which rotates the output shaft two full
rotations, stopping at each extreme. Do not confuse these
with “360 degree servos” — an alternative and unfortunate
term for continuous rotation servos.
Linear servos are controlled by standard servo signals
and come in different sizes — from the tiny Spektrum in
Figure 8 to the giant Firgelli in Figure 9. EMS sells a $10
kit to convert a Futaba S3003 to linear, or you can buy the
smaller VS- 19 Pico linear servo for the same price.
Power servos are monstrous stump-pulling affairs. If
power is your primary concern, ServoCity’s $240
SPG7950A-BM offers an astounding 3,402 ounce-inches of
SERVO 07.2015 73