MrRoboto - Oct 11.qxd 9/1/2011 3:39 PM Page 14
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by
Dennis Clark
I’m going to kill a few birds with one stone this month.
I’ve been quizzed on converting a toy into a robot (always
fun, and I don’t have to design the mechanical!), PWM
creation for cheap motors, and basic robot “vision” sensors.
I’m going to answer all these questions at once with a little
project that I did in two phases, a couple of years apart.
I’m going to show you how I converted a toy IR remote
control spider into a robot that won’t walk off the edge of
a table. This is a fun one for the kids.
Speaking of kids, this robot was built with the intent of
making it as robust as the toy was, with all electronics and
batteries, wires, etc., fully enclosed. Nothing to break! My
little spider has withstood the test of time with Pre-K kids,
Kindergarten, and all the way to fourth grade students,
without a single failure. I’d call that a success! Let’s begin!
Figure 1 shows the spider as it came in the box from
Figure 1. WowWee spider.
Wow Wee toys. These folks come out with the coolest
platforms to hack into robots. They are the company that
gave us RoboSapien, RoboReptile, and many others. I
applaud their gifts to the robot hobbiest.
Quite by accident, I found a spider that didn’t have the
silver paint on it, it was all red – perfect! The first thing I
did was completely strip out the electronics that it had in it.
I left the array of LEDs on the bottom (which I’ve not found
a use for yet), the motors (two of them), and the battery
pack which was molded in anyway.
This is a fascinating platform. There are two motors,
each of which runs a side of legs. The thing walks by
alternately lifting pairs of legs on each side. When the
motors are in sync, it walks straight. We all know that
without feedback, no two motors EVER run at the same
speed, so the spider often kind of “crabs” to one side. It
does mostly run well, and quietly, and kind of creepy.
Perfect for kids and robots.
After you remove the
original “guts” of the spider,
you are left with precious
little space, so think carefully.
I designed this controller with
through-hole components on
a simple prototyping board. I
could do a lot better with a
specially designed PCB or
even surface-mount devices,
but this was a “one off”
project for fun, so I broke out
the soldering iron after I
figured out what I wanted.
I started with a simple
microcontroller design
running a 754410 dual H-bridge chip at 1 kHz PWM
rate. I then added one of my
custom IRPD boards, carved
and shrunk down. For the
14 SERVO 10.2011
