10 SERVO 10.2013
Q. I want to make a walking robot. I’ve looked at hobby servos and they don’t seem
to be a good match for this project.
I want some kind of feedback so that
I can balance while walking, and I
don’t want a huge bundle of wires. Is
this possible? Are there servos that
can give me that information?
— Bobby via email
A. Bobby, I like where you are going with this, and yes, there are servos that can offer a great
deal of feedback on not only their
position, but current draw, heating,
and other useful data. Let’s look at a
few! (There are more, but the ones I’ll
discuss are the servos that I found
First off, let’s look at hobby
servos and see what they offer. Hmm,
My research also shows that only
one of the major (and minor) makers
of servos offers a contiguous bus
configuration to minimize wiring. That
one manufacturer is Futaba which has
its S-bus receiver and servo system.
The S-bus system allows S-bus servos
to be programmed to know their
location in the system.
Further, the servos reside along a
single three-wire cable connected to
the receiver. There are also S-bus
translators that allow non-S-bus servos
to be used in an S-bus system.
That’s nice, but these servos are
expensive and still don’t provide
position or force feedback.
Now, we’ll move on to intelligent
networked servos that you don’t have
to continually send pulses to in order
for them to continue to function.
I have an admission to make. I
know of three bus-networkable robot
actuator systems. There may be more,
They are the Robotis Dynamixel,
RoboBuilder wCK, and Dongbu
HerkuleX. The Dynamixel, HerkuleX,
and wCK servos come in a variety of
strengths and speeds. You can create
a microcontroller interface to any of
them (they all use standard UART
protocols; either straight digital or
Before we go into any kind of
details, here is where you can find
programming information on all of
Dynamixel AX- 12
Table 1 shows these servo
actuator systems and their overall
notable abilities. Each of these servo
actuators have many more settings
that you can configure, including the
ability to get multiple servos to act at
the same time, set motion limits,
torque limits, and error conditions. It
is a good evening’s time in the arm
chair of your choice to read through
all of the possibilities.
It seems like every week there is breaking news from a Japanese or Korean lab dealing with walking bipedal robots. Awesome! In the US, there is news from "leg labs" from time to time, and more details about military robot "horses" that carry loads and sound like large leaf-blowers chasing you.
(Is that a prelude to some kind of movie or perhaps nightmare?) If you’ve come
to the conclusion that I'm a bit biased towards more mundane uses for robots,
you'd be right. Robot assistants for people who have lost the ability to walk or
use their arms, or could use a little help around the house seem far more worthy
endeavors than new, improved ways to kill people. However, just to prove I'm not
completely consistent, I love the new RoboOne competitions with robot Sumo,
wrestling, and boxing matches! Our question this month is from a reader who
appears to be thinking along these same lines ...
by Dennis Clark
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