22 SERVO 01.2017
Igot my BS in Mechanical Engineering from Virginia Tech in 1982 and promptly went to work
for Mattel Toys designing Hot Wheels
track sets for the next 30 years. I have
a knack for scratch-building and
prototyping new electromechanical
concepts. I built my first
programmable robot in 1994 using a
then-new Parallax BASIC Stamp 1 with
a whopping 256 bytes of program
memory. That ugly old robot in Figure
1 won the very first Robot Firefighting
Contest in Connecticut, which later
became the Trinity College Home Fire
Fighting Robot Contest — still going
strong after 20+ years. Highly
recommended, contests are lots of
fun and you meet some great people.
These days, I’m an independent
inventor and freelance designer, and I
scratch-build robots and
electromechanical gizmos almost
every day. I still like and use Parallax
products. Some of my minimalist
robots use tiny PICAXE chips. I’m
“erco” in both of those online forums,
swapping ideas and comparing notes
with like-minded robot folks.
I’m a compulsive hoarder of all
robotic treasures I find online: chassis
from China, sensors from Shenzen, H-bridges from Hong Kong, motors from
Macau, and transistors from Thailand.
I’m into simple clever
electromechanical solutions: one servo
robots, combining I/O pins, using the
odd relay, direct drive, dead
reckoning, flamethrowers, and, in
general, breaking the rules!
I hope you’ll find some useful
information here. If you have any
specific or general robot questions,
email them to me at
email@example.com and I’ll
do my best to answer them.
Q. I have seen the term “PID loop” used in describing motor/sensor relationships.
Can you explain what a PID loop is
and why it would be needed for
A. ‘PID’ is an acronym for Proportional, Integral, and Derivative control. These are
three separate components of a
closed-loop (feedback) control system,
the purpose of which is usually to
deliver smooth and stable control to a
mechanical system. There are books,
websites, and college curriculum on
control systems, so I can only scratch
the surface here in hopes of whetting
your appetite. I’ll play the same ‘get
out of jail free’ card as many of my
college textbook authors: “It shall be
left as an exercise to the reader to
prove that ...”
You can watch https://www.
Gy8 for a helpful tutorial. Everything
is better with an Aussie/Kiwi accent!
Closed-loop control systems come
in many flavors. They are dynamic
(always changing) and the output has
a desired setpoint. The actual output
is measured by one or more sensors,
and the error is used by the control
system to nudge the output in the
proper direction through electrical
Mechanical systems have a
response time — an indicator of how
quickly the output responds to a
change in input. Overshoot and
oscillation are visible measures of
control system effectiveness. In
robotics, PID is useful for smooth
motion control. One particularly
demanding PID application is a
balancing robot (inverted pendulum).
Gyros, accelerometers, sensor fusion,
Kalman filters, the works. That’s a
complicated subject worth spreading
over several magazine articles. Let’s
start with a more graspable
application: a line following robot
(LFR). There are LFR contests at robot
shows where the fastest bot wins.
Consider curvy courses instead of
straight lines with 90 degree turns.
You can find plenty of “Line Follower
Competition” videos on the web.
It’s not difficult to make a slow
by Eric Ostendorff
Our resident expert on all things robotic
is merely an email away.
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answered here! From software algorithms to material selection,
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Ask Mr. Roboto
Hi! My name is Eric, but you can call me Mr. Roboto. I’ve been a robot nut my whole life. I grew up
playing with toy robots and watching Lost in Space, learning that any mistake can be undone by
reversing the polarity. The toy robots I collected in the 1960s were all mechanical: Bump & Go
“Mystery Action” robots and “Rotate-O-Matics” which would walk straight, rotate about the waist,
and fire light-up machine guns. Since then, my collection of vintage toy robots has grown into a small
army you can see online at