of bright reflective aluminum tape and shiny
chrome duct tape which should also be easy to detect
against most any flooring color.
Second, following walls is pretty straightforward using
either bump switches or infrared/ultrasonic sensors (all
cheap and readily available). Simple electronics adjust your
motor speeds to curve left/right based on whether you
sense a wall. See my robot follow a wall using a Sharp IR
sensor at https://www.youtube.com/watch?v=
Like the stock line followers, wall followers may never
really go perfectly straight, but eventually they will get
there. If you need to get across a doorway or around a
corner, some experimentation and timing calibration can
get you across a gap from the safety of one wall to the
next. Get jiggy with it!
Third, the minimalist in me loves the tricycle chassis.
Driving and steering just one front wheel (Figure 4)
simplifies everything, as you can see in the figure 8s
demonstrated at https://www.youtube.com/
watch?v=MPAkAzu Y0Bc. Steering is controlled using a
standard servo, which is very accurate and repeatable.
I won that Coasterbot contest mentioned previously
with a tricycle chassis. Here’s one of the simplest tricycle
robots I ever made, using a BASIC Stamp 1 board and a
mechanical switch for a wheel encoder: https://www.
youtube.com/watch?v=hz Ng YpJdfDs and
Okay. Let’s get back to the original problem of syncing
two wheels. Around 2004, Parallax introduced an encoder
kit for the Boe-Bot ( https://www.parallax.com/product/
28107). The kit adds amazing functionality to the robot,
and application notes are solid gold for anyone who wants
to delve into the mathematics of navigation, and
determining distance and direction using encoders. Check
I took it upon myself to add wheel encoders to a
Parallax Scribbler 1 robot back in 2009 (https://www
. youtube.com/ watch?v=5r2En4hLUBI). Then, I made a
much larger robot with wheel encoders in 2010
watch?v=PX0IhUqnwrk). I DIYed
those wheel encoders using the
wonderful — but very hard to find — Hamamatsu P5587 IR
photosensor ( http://www.junun.org/MarkIII/
Both of these BASIC Stamp 2 powered robots worked
very well — even if the Stamp had its hands full counting
every single pulse on two encoders and adjusting the motor
speeds to match. Missing a single pulse would cause
problems. I made it my personal quest to see how fast a
BS2 could count encoder pulses, frying a poor DC
gearmotor in the process. Check out the videos at
_V5jdPE. Jolly good fun.
Around this time when I was obsessed with odometry,
I sprung for a 1999 vintage CYE robot (Figure 5). This
unique and amazing robot is the ULTIMATE in odometry
and simplicity; see www.pioneernet.net/johnc/
cyenavigate.htm. Inventor Henry Thorne made Cye
navigate through a real household environment without any
external sensors at all — just motor encoders — while linked
to a host PC.
Cye’s navigation was based on the rectilinear layout of
most houses, triangulating and planning the best path from
point to point around walls and known obstacles. Options
included a sound sensor to count handclaps, a vacuum
cleaner (Figure 6), a wagon to haul things (Figure 7), and
a wireless camera ... in 1999! Yes, telepresence and
vacuuming were both available last millennium! For
reference, iRobot’s Roomba robo-vac debuted in 2002.
The best videos I can find are a modifed Cye at
a Cye wagon-pulling coffee server at https://www.
youtube.com/watch?v=QSMNQqAzP-I. Amazingly, it
uses nothing but motor encoders to drive each wheel,
update its position, and map your entire house.
Long before LIDAR and SLAM (Simultaneous Location
and Mapping), there was Map-N-Zap (Figure 8). The whole
Cye robot system, path planner, and Windows GUI were
ahead of their time.
A simple charging home base (just a pair of contacts
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