Figure 1. The disassembled VHS cassette.
tapes probably planned it that way. The two tape reels
were the perfect size for wheels. The body of the tape is a
good size for the frame and there is even a long strip of
springy steel that would make a perfect bump sensor
The first step was to rip out all the tape from the reels.
This takes a surprising amount of time and you may want
to enlist the finely honed skills of a two-year-old child in
this endeavor. Once the reels are empty, cut the tape
from the reels and throw it away. The rest is a matter
of personal style and available materials.
I first pulled some servos from an old robot frame.
These servos had already been modified for continuous
rotation. I cut rectangular holes in the side of the
cassette tape body for the servos and drilled a couple
of holes for the mounting bolts. Next, I drilled a small
hole in the center of each reel. I bolted the servos to
the body, and then removed the screw from the servo
horn and used it to screw the reel to the servo. (Rinse
and repeat for the other side.) A ping pong ball hot
glued to the hole in the bottom front of the body is
the third "wheel." This works quite well for a small light
robot that generally stays on smooth surfaces.
The bump sensor is very simple but effective. I
drilled a couple of holes in the front of the case using
the holes in the spring strip as a guide. Then, I bolted
the strip to the front of the case (Figure 2). I used a
wire under the nut to connect the strip to ground on
the controller. For the other half of the bump switch, I
used duct tape (the aluminum tape for real duct work).
If you don't have a roll, you need one now. Just
remember the glue on the sticky side is a pretty good
insulator, so make connections on the top. I cut a
couple of strips, stuck them under the bump sensor
spring on each side, and ran the excess under the body
of the bot. Then, I used another piece of tape to stick the
Figure 2. Open cassette case showing
mounted motors and sensor.
stripped end of a wire to the duct tape (Figure 3). A pullup resistor and some wiring complete the sensor
The battery is from a 9.6V rechargeable pack that I cut
in half lengthwise to make a flat 2x2 4.8V pack. I have had
good success running 5V microcontrollers from a 4.8V NiCd
pack without any voltage regulation.
SERVO 02.2010 49