lot of nice stuff, and some of it is amazingly inexpensive.
• XBee Explorer regulated
• XBee Explorer USB (only one for main PC)
• XBee 1 m W Chip Antenna
• Motor Driver 1A Dual TB6612FNG
• Flex Sensor 4. 5”
• Arduino Pro Mini 328 — 3.3V/8 MHz
In our hamster's inner workings, we have an Arduino
orchestrating communications between the main host
processor — in this case, a PC — and the H-bridge via the
XBee. The Arduino runs a simple bit of code that acts to
control the PWM signal to the H-bridge to give very simple
acceleration and deceleration profiles. It also acts as a
watchdog timer, shutting the motors down if no
communications are received. Eventually, we will also install
a battery monitor so that we do not destroy our precious
Lithium polymer batteries. The XBee modules are
communicating directly to the host, and no mesh networks
FIGURE 2. AR marker being recognized and overlaid
74 SERVO 04.2010
ratings. These batteries may just save us from a total
Making Sense of Things
Now that I’m well on my way to building an army, this
mercenary of mischief is tired of being a lone soldier on a
mission of madness. I need a general to help in the
marshalling of my gerbil troops. For this foray to the edge
of sanity, I look to my co-worker Scott Nichols for help with
ideas and programming. I will leave the writing and
building for myself.
Let’s talk sensors. We want our gerbils to be well
outfitted. Rotation sensors on the wheels to track position,
maybe a magnetometer to sense absolute orientation.
Range sensors to determine distance to other obstacles.
Perhaps even cameras to better understand the immediate
surroundings, or at the very least, some primitive color and
light sensors. The problem is this all gets very expensive,
complicated, battery hungry, and heavy very fast. This is
where sensor virtualization comes in. For example, if I were
to add an accelerometer, compass, several distance sensors,
and wheel encoders, I could easily add $200 to the budget
for each hamster.
In concept, it is fairly simple. A camera mounted over
the hamster habitat senses the position and orientation of
every hamster in the environment through the use of
fiduciary marks affixed to the tops of the hamsters. These
fiducial marks actually provide complete six degree-of-freedom pose information that could, in fact, be used to
provide a complete multimedia augmented reality
experience. For now, though, I think we’ll concentrate on
just detecting the pose of the targets.
Doing some research into augmented reality has lead
to a lot of stalled development. It seems like there isn’t as
much open source development going on as I had hoped.
Most everyone involved in it seems to have gone the way of
developing for private use or for mobile and industrial
applications. This should not be a problem for us, though,
since our needs are really quite modest compared to the
capabilities that exist in the private sector. I did find the
book Augmented Reality: A Practical Guide by Stephen
Cawood for $23 on Amazon. It promises a download of
their SDK for private use, but the SDK isn’t for distribution.
Another option is ARtoolkitplus at http://studierstube.
Any marker can represent anything. Here are a few
for representational purposes.