threads is the “Figure 8 Challenge” at http://forums.
challenge. The premise is that getting a robot to drive an
accurate figure 8 (usually a right circle, then a left circle, or
vice-versa) by dead reckoning is harder than most people
think. The “challenge” is simply to share a video of your
robot doing (or attempting) a figure 8.
Ideally, you end up exactly where you started. There
are no rules. Any robot, any processor, any size, any size
circle, indoors, outdoors, etc. One guy even had his robot
arm draw a figure 8. It’s all about fun and creativity. Feel
free to view the many entries there, and join the fun if you
like. Lurkers are always welcome.
For accuracy and repeatability, a closed-loop (feedback)
electronic control system is used to synchronize the wheels
by detecting which wheel gets ahead, and adjusting motor
speeds to match. Encoders are sensors which measure how
far a wheel or motor has rotated. By constantly monitoring
both wheels, you can travel in a straight line, measure
distance travelled, and/or measure how much you have
It’s a big deal,
the cheap kits
(Figure 1 again;
red circle) for
potential use with
but nothing ever
becomes of them.
The kid (I mean roboticist!) programmed a path using a
membrane keypad. Original Big Traks and accessories are
still revered by collectors and fetch good prices on eBay.
The “Recon Rover” (Figure 3, right) is a similar modern toy
which also has a tank-like form factor and real rubber tank
Like Big Trak, it has built-in encoders and is
programmed through a membrane keypad to follow a
specified path. A great educational STEM item, it comes
with an LED screen, a nicely-done “mission manual,” and
even a tape measure to guide the builder through a series
of lessons in dead reckoning. It’s Mr. Roboto-approved, and would make a dandy Christmas
gift for any budding roboticist. Back to DIY.
Let’s look at three simpler alternatives to
wheel syncing to get from A to B.
First, following lines is VERY easy. I’ve
covered $5 line follower kits in recent
columns; these are fun and work well. If you
can live with a tape “track” between your
rooms, this is the fastest and cheapest way to
get something going.
Most line followers like to use a black line
on a white background, but with some
hacking, most anything can be made to work
— white line on a dark background or any
high contrast line. Here’s a video of my
hacked Scribbler following white tape on a
tan carpet: https://www.youtube.com/
watch?v=8WyM6iUrSg0. I’ve seen samples
10 SERVO 12.2017