www.servomagazine.com/index.php?/magazine/article/december2011_Bunting
Discuss this article in the SERVO Magazine forums at http://forum.servomagazine.com
FIGURE 1. Inside the Dimension 3D
printer as it finishes up a femur,
tibia, and coxa.
Original
Setup
The following summer,
I began work at the Robotics
and Neural Systems Laboratory
(RNSL) under professor Dr.
Anthony Lewis, who taught the course where I built
the Q-Learning hexapod. Many of the robots designed
in the lab were built using the Dimension BST 1200ES
3D printer created by Stratasys. Naturally, anticipation
started to build as I began thinking of ways of
upgrading the hexapod. Originally, I had brass pieces
purchased from my local hardware store soldered
together with mechanical components not being quite
as symmetric as I had envisioned. I knew that a full
robot makeover was in order, so I began doing some
research of other upgrades to implement. Figure 1
shows the 3D printer extruding some of the first
hexapod leg components. Figure 2 shows the progression
from the original brass femur to the current split design
femur.
The hexapod had been transformed from a
Frankenstein mixture of parts to something very similar to
what I have now. The Dynamixel series of motors from
Robotis had been a clear decision for me since I
purchased my first one six months prior to the upgrade.
The idea of a tunable motor with error checking,
temperature, and overload sensing with position feedback
into the computer on an easy to wire daisy-chain communication bus was a
dream for most hobby
roboticists. Robotis made
that a reality.
The total motor count
consisted of six RX-10s, six
That implies the possibility of sending and
receiving more than 100 read and write commands in the
time it takes a regular servo motor to register one
standard PWM cycle.
Compulab had just announced the release of the
fit-PC2 just days prior to my decision to add an onboard
computer for processor-intensive vision computations. The
Atom z530 processor can easily crank out multithreaded
code on a full Ubuntu install, while the whole computer
only consumes five watts of power. It is possible to view
the hexapod as basically a walking case mod.
The hexapod was my first computer to have Linux.
There was a bit of a learning curve, and even after a
few years I am still discovering what I can do, but
even more importantly what not to do. I
highly recommend using Linux, as I
have been able to get very
advanced behavior while
maintaining low level
control on a well
supported, free
operating
system.
The
camera I had
previously
used was a
Logitech Quickcam
Communicate Deluxe.
Though a great camera
that works seamlessly with
Ubuntu and OpenCV, I grew tired
SERVO 12.2011 57
FIGURE 2. Various femurs produced from iterative
design. The femur at the top left is the original brass
femur. Over time, the femur has evolved to the split
design on the lower right.
