by Fred Eady
UNWINDING
THE AX- 12+
COMMUNICATION
PROTOCOL
I love to write robotic driver
firmware and scratch build PIC
microcontroller-based robotic
hardware to run it. In this
edition of SERVO, we’re not
only going to sharpen our
driver authoring skills, we’ll
also get some flight time on
the handle of a soldering iron.
Icollective programming and hardware design/assembly
efforts will be focused on the Microchip PIC18F2620,
n the discussion and hardware build-up that follows, our
which will be coded to drive a Dynamixel AX- 12+ robot
actuator. There are several Dynamixel robot actuators in
addition to the AX- 12+. This month, we will center
exclusively on instructing the F2620 to drive a Dynamixel
AX- 12+ robot actuator. We’ve got some specialized AX- 12+
hardware to design and assemble before we can begin to
code the driver firmware. So, let’s get started.
The Dynamixel AX- 12+
I can easily describe the Dynamixel AX- 12+ robot
actuator you see in Photo 1 with a single
word: SuperServo. The AX- 12+ can do
everything a standard hobby servo can and
better. For instance, to obtain continuous
rotation you don’t have to disassemble and
intentionally “break” it. You simply command it to perform an endless turn. Need to
know where the servo shaft is? Don’t ask a
hobby servo, because unless it’s one of the
new digital models, it can’t tell you. A
Dynamixel can not only tell you where its
shaft is, it can also tell you if it’s moving.
In that you’re reading this magazine,
odds are that you have some prior exposure
to hobby servos. For those experienced
readers, you know that hobby servos move
at their own mechanical pace with a set
amount of torque. The Dynamixel can be
PHOTO 1. The daisy-chained one-wire RS-232
link I am referring to is actually a DATA line and
a GROUND line. The AX- 12+ also distributes
power on a third daisy-chained line.
30 SERVO 04.2009
