test a left turn circle (counter-clockwise) and slowly slightly
adjust R1 clockwise until it follows the turn properly. Then,
go back and retest right and left turns.
There is a best balance of pot adjustments which will
let the robot track properly right and left. Once you get it
dialed in, you can try speeding it up. One of my videos
shows that faster speeds come from using higher voltage
Li-Ion cells (~4V) compared to the stock 3V alkaline cells
(recalibration required). How fast can YOU go?
Sadly, as I write this, RadioShack stores are having their
final clearance sales, and I bought a “Running Microbug”
kit for $15 (cat #2770353, Figure 8). This minimalist robot
kit uses direct drive from two small square motors: no
gears, no wheels. The motors tilt
down so that their shafts touch the
ground, becoming the world’s
smallest wheels (Figure 9). Clearly
not suitable for carpet, this is a fast
robot for a smooth open floor.
While quite functional, the open-frame motors are practically dragging
on the floor and easily pick up hairs,
dirt, and anything metallic. I found
this out the hard way and had to
carefully de-gunk two greasy
I would recommend enclosing
the bottom of the motor with a piece
of scotch or electrical tape to keep
This must be done carefully to
avoid taping the armature in place.
Make a convex pocket in the tape
and/or make a non-sticky spot on the
tape (paper, tape dot) where it might
PCB sure makes a classy chassis with part outlines and
numbers in red ink. The small fold-out book gives step-by-step instructions.
Construction takes 30-60 minutes with two novel
elements. First, the square metal motor cases are fastened
to the chassis at oblique angles by solder only. You’ll need
a big iron and some attention to detail to mount both
Second, the tail roller uses a big fat barrel diode for an
axle (LOL). It’s soldered in place for mechanical function
only, but I think it would have been clever to use it in the
circuit for something.
After a smooth build, I was prepared to be wowed.
Straight off the Shack’s website: “This
photosensitive microbug follows light and stops in
darkness.” To me, that clearly means that it will track
towards a light source. Heck, I’ve already done that with
two photocells and one servomotor:
Surprise, surprise, however. Here are the exact operating
Switch on to play. If you want Microbug to turn and
circle left, fully turn the potentiometer on the right. This
then dims the LD resistor and stops the motor on the
right. To run and circle in the opposite direction, fully turn
the left potentiometer. The brighter your surroundings, the
faster Microbug runs.
YOU GOTTA BE KIDDING ME! This doesn’t begin to
describe or take advantage of this robot’s components or
function. This is neither educational nor fun. Where’s the
SERVO 07.2017 11
Design New Ideas
Cut Real Metal
120VAC - Plug in