I am an emeritus professor of mathematics
at the University of Wisconsin (and a maker!). My
research has largely focused on the thermodynamics
and mechanics of heat engines. Stirling engines have
been at the heart of all this work. They are of both
theoretical and practical importance — and are fun
to make! So your recent article in MAKE, Volume 17,
“Teacup Stirling Engine,” caught my attention.
Although the basic Stirling principle goes back
nearly 200 years, the appearance of Stirling engines
capable of running on low-temperature heat sources
(like a cup of hot tea) occurred only within the last 26
years. I was privileged to work on the development
of these engines, producing in 1991 a Stirling engine
that runs with a temperature differential of only 1°F.
A year later, I made a model for NASA optimized to
run on the warmth of human hands. NASA used this
model (dubbed the N- 92) to demonstrate Stirling
engine principles as they contemplated the use of
advanced Stirlings for powering space stations and
planetary vehicles from solar or nuclear energy.
An Introduction to Low Temperature Differential
Stirling Engines provides complete plans and tips
for making the NASA N- 92 engine. It also tells and
illustrates the complete story of the development of
these fascinating engines, which began in 1983 with
the late Prof. Ivo Kolin of the University of Zagreb.
—James Senft, Ph.D., Emeritus Prof. of Mathematics
University of Wisconsin-RF, River Falls, Wisc.
rotate the camera to the right position and click
the shutter, rather than mess around with Silly
Putty for an unreliable timer.
Second: the card reader. I have an electronic
workshop where I build electronic gadgets, not fix
TVs. I already have most of the material called for,
however I’ll substitute a 74LS541 for the 74541
chip you call for. It’s the same circuit and will run
on 5 volts. A 7405 voltage regulator wastes a lot of
current at 9 volts; how about four AAA batteries in
series at 6 volts to the regulator, or a 4-cell rechargeable telephone battery? Don’t cost much and it’s
available at RadioShack.
—C.P. Furney, Jr., age 81, Oak Ridge, Tenn.
In Volume 18, page 22, “Trailer (Re)Made,” the
trailer was bought through the General Services
Administration (GSA), not the Government
Accountability Office (GAO). In fact, GAO investigated
problems with FEMA trailers.
In Volume 18, page 159, the Toolbox article “World’s
First Embedded Power Controller” should have been
titled “Playing with Configurable Analog/Digital
Chips” and displayed a picture of the First Touch Kit
rather than the Cypress Power PSoC.
In Volume 17, page 137, “Elastic String Bass,” the
online schematics at makezine.com/17/diymusic_
elasticbass have been corrected to show 440Ω
resistors, not 440K resistors.
Very neat concept. Keep going! First comment:
the print is too small. I’m an old man, but it’s too small
for anybody. Looks like the fine print of a legal doc.
I am looking at two projects in MAKE, Volume 01.
First: the kite camera. But I think I’ll get a radio
controller from a model airplane or model car to
CLARIFICATION: In Volume 17, page 136, “ 1+ 2+3:
Mechanical Image Duplicator,” some readers mistook
the second paper clip box for a second fixed anchor.
It’s simply a spacer to keep the duplicator level.
With just a single anchor at the far left (as shown in
Figure 3), the duplicator works great.