skranish
Nov 01, 1996, 01:00 AM
<p><font size="4"><b>Introducing 'From the Lab'</b></font> </p>
<p>Welcome to 'From the Lab', the first monthly column on electronics and equipment for
electric flight. This column will discuss motors, motor controllers, batteries, chargers,
radio equipment, measurement instrumentation, and pretty much anything else electrical or
electronic that has an application to electric powered aircraft (and other types of
models, too!) </p>
<p>I have some ideas of what I would like to write about, but I would really
appreciate some feedback from my readers so that I can fly this column in a direction that
you would like it to go. </p>
<hr>
<p><font size="4"><b>Introducing the Columnist</b></font> </p>
<p>My name is Steve Kranish. I grew up in the Washington DC area (I'm from Chevy Chase,
and you're not!), where I was a member of DCRC. I tried to build a few Comet kits when I
was quite young, but my first successful flying models were the model rockets I started to
fly in about 1966. I became involved in RC a few years later, when I purchased a
second-hand Testors pulse system. I don't think I ever successfully flew anything with
pulse gear, but I did try for quite a while, and still have a box of Rand galloping ghost
actuators, Ace pulse actuators, Benterts, and Albins. If you know what those are, well,
you have been at this as long as I have. My first 'real' radio was a Royal 70 Series
purchased as a kit in about 1971. Just for perspective, that radio cost over $200 in 1971
dollars, as a KIT! An entry level new car cost about $2000 in those days, so the
equivalent today would be $800 to $1000. It was NOT a cheap hobby back then! </p>
<p>In the early '70s I flew a variety of model types, and was fortunate enough to meet the
editor of American Aircraft Modeler (AAM), which was based in Washington at the time. I
built a number of models for reviews, which allowed me to try some model types that I
could not otherwise afford. I built a number of ARFs (hey, they were free!) including some
.60 size pattern planes, but eventually drifted into sailplanes. While I was a freshman in
college, I built a Graupner Hi-Fly for a magazine review. Although nominally a sailplane,
the Hi-Fly came with complete instructions for conversion to electric, which was a real
novelty in those days. The electric equipment did not come with the review model, so mine
was built and flown as a sailplane. I still have the model, and it may yet get an electric
setup similar to that shown in the plans - twin pusher Speed 400s with gearboxes, with the
motors mounted at the wing trailing edge. </p>
<p>My work for AAM actually did include building some of the earliest electric airplanes,
although they were all done for the magazine and I never flew any of them. At the time
electrics seemed very expensive, and I was mostly flying gliders off of high starts. The
most memorable of these electric projects was a Kaos 40 pattern plane, converted to
a twin (tractor) electric, with the motors mounted to the wing leading edge. The
plane was trimmed out to look like a transport - I still have photographs, and will
probably include one in a later column. </p>
<p>My interest in model rockets and RC converged with the 1981 Space Modeling (Model
Rocket) World Championships, where I was an alternate to the US team. Try to imagine an 8
ounce vehicle, with 4 ounces of rocket motor, 2 oz of airframe, and 2 oz of radio.
Climbout is vertical, to about 1000 feet in 10 seconds or so. </p>
<p>I drifted out of modeling for a number of years, but never discarded any of my
equipment or planes. The arrival of my son started a 'second childhood' and after flying a
very old Airtronics Square Soar for a few months, I bought a Graupner Elektro-UHU kit.
Actually, I bought all (3) of the electric and sailplane kits at the local hobby store,
because they knew they were never going to sell them. (Typical brain-dead hobby shop that
just sells .40 size trainers.) I built the UHU in about a month, and have been firmly
hooked ever since. </p>
<p>Most of my current flying is at local schoolyards, so electric is the only way to go.
The big fields where I used to use a high start now have buildings on them, anyway.
I frequently fly on the athletic fields that adjoin the center where both of my children
go for day care. At 7:45 AM, no one is there, and since I don't make any noise, no one
seems to mind. The fields are close cropped grass, and the only obstacles are soccer goals
and trash cans. (The UHU has scored one point so far.) </p>
<p>My early interest in RC provided me with a direction for my education and profession. I
have a BS degree in Electrical Engineering from Cornell University. I bounced through
a couple of short lived jobs, including one writing video games, and have been
an engineering consultant for the last 13 years. I presently try to concentrate
on embedded system hardware and software, but I have done everything from Windoze
programming to designing kitchen appliances to digital audio systems used in nuclear power
plant control room training simulators. If you need help on an engineering project, feel
free to contact me. </p>
<p>I had always hoped to work in the RC industry, but while I was getting some experience
as an engineer, the domestic industry went poof. I did get to design the battery
cycler/charger sold by Royal Electronics in the early '80s. I have also designed a very
sophisticated servo tester that can even measure deadband, and a sophisticated
microcontroller based throttle, but neither of those have been commercialized - yet. </p>
<p>I presently live in Beverly, MA, about a 10 minute walk from the Atlantic Ocean in a
house that I share with my lovely wife, two children, ages 1 and 3, (who had better
develop an interest in models), two cats, and more airplanes, kits, and equipment than I
care to think about. </p>
<hr>
<p><font size="4"><b>My Current Airplane Fleet</b></font> </p>
<p>Just to give you an idea of what sorts of electric powered airplanes I am interested
in: </p>
<p>I currently have in flyable condition, or close to it:
<ul>
<li>NSP Neon 400, a Speed 400 class sailplane </li>
<li>Graupner Elektro-UHU, with a Speed 600 direct drive motor </li>
<li>Today's Hobbies Skyvolt, with an Astro Flight 05 </li>
</ul>
<p>In the next few weeks, I should have flying:
<ul>
<li>Griggs Model's Rocket, a Speed 400 class pylon racer </li>
</ul>
<p>My projects for the next year or so include (in New England, we have a real building
season)
<ul>
<li>Great Planes Spectra (I already have a Spirit, so I will just re-use the wing), probably
with a geared Speed 600 </li>
<li>Bridi EZ-1 2Meter Glider, converted to electric </li>
<li>another Griggs Rocket </li>
<li>Midway Models Commander Old Timer </li>
<li>an Elektro-UHU derivative with a larger foam wing </li>
</ul>
<p>I actually have a LOT of other kits and planned projects, but this is about all I can
reasonably expect to tackle in the next year. </p>
<hr>
<h2>My Current Interests </h2>
<p>I am primarily interested in electric sailplanes. My recent experience with the Skyvolt
has convinced me (again) that I am just not an airplane type. Somehow, 5 minutes of
erratic, sloppy aerobatics per flight just doesn't do it for me. What else is there
to do? It does not have the power for touch-and-goes off grass, and it runs down the
battery too fast to justify flying slow circles. With a sailplane, the same challenge is
always present: how long can I stay in the air? In still air I can get 16 to 17
minutes with the Neon, so there is more air time and less ground time. </p>
<p>I have a long term interest in nicad battery capacity measurement, dating from my
design work on a Cycler/Charger for Royal Electronics. This is a topic I will definitely
write about, and I may yet design some commercial products for this area. </p>
<p>I am also interested in motor controllers - they are REALLY throttles, but more on that
in a future column. I have a very good design running on the bench, pending some decisions
about what exactly I should do with it. It may yet appear as a product, but at the
minimum allows me to write about controllers with a full understanding of how they work,
and what sort of tradeoffs are made in their design. </p>
<hr>
<h2>Reader Survey </h2>
<p>I am really writing this column for you, the reader. Unfortunately, I do not currently
know who my readers are, what there interests are, or what their level of technical
expertise is. </p>
<p>If you would like to be part of a reader survey, please copy this section of the column
into an email message, and email your response <i>directly to me </i>(NOT TO THE EFLIGHT
LIST) <a href="http://rcgroups.com/shared/nospam.php?u=skranish&d=world.std.com">skranish(at)world.std.com</a>. </p>
<p>How long have you been flying model airplanes? </p>
<p>How long have you been flying electric airplanes? </p>
<p>What size airplanes are you flying? (Speed 400, Astro 05, Astro 60, converted washing
machine motor?) </p>
<p>What DON'T you like about electric airplanes? </p>
<p>How many flyable planes do you currently have? </p>
<p>Are there any planes you particularly like/liked? Any you particularly disliked? </p>
<p>How many NIB kits do you have? How old is the oldest one? (my answers are
embarrassingly large!) </p>
<p>Do you want to see any math in this column? Would you prefer that I avoid math
entirely? </p>
<p>What sort of math tools do you prefer: sliderule, calculator, spreadsheet, MathCAD,
canned program, finger counting? </p>
<p>Do you know what amperes and volts are? Can you explain the difference? (yes or no will
do, I KNOW the difference) </p>
<p>Do you want to see software code as part of this column? Schematics? </p>
<hr>
<h2>Future Columns </h2>
<p>I would like this column to contain material of interest to the reader. Here are a
few proposed column topics:
<ul>
<li>What is wrong with BEC, and what can we do about it? </li>
<li>Cell Impedances: why the published specs are wrong, and what you REALLY should know </li>
<li>Battery Capacity: how to measure it, what affects it, and what it all means </li>
<li>System Impedances: connector and wire differences and realities </li>
<li>What REALLY limits the capabilities of a motor controller and BEC </li>
<li>Measuring motor and prop performance - the tools you REALLY need </li>
<li>Why Airplane motor controls are so different from car and boat controllers </li>
<li>Converting an inexpensive timed charger to peak detection </li>
<li>Selecting an appropriate drive train - It all depends on what you want to do with it! </li>
<li>Airplane Building Tools - What works, what doesn't, and what you can't live without </li>
</ul>
<p>If there are other topics you would like to see, or some of the above that you DON'T
want to see, please email your response <i>directly to me </i>(NOT TO THE EFLIGHT LIST) <a href="http://rcgroups.com/shared/nospam.php?u=skranish&d=world.std.com">skranish(at)world.std.com</a> </p>
<hr>
<h2>Wiring Your Own Battery Packs </h2>
<p>Nicad battery packs can be a major expense for an electric flight modeler, especially
if you build a lot of different types of models, and each requires a different size or
form factor battery pack. One way to save money is to assemble packs yourself, especially
if can buy appropriate cells second hand. </p>
<p>Gordy Stahl in Louisville, KY at 502-491-5001 sells used Sanyo (and some Panasonic)
1000SCR, 1400SCR, and 1700SCR cells for about $2 each. The cells are either individual
cells or spot welded packs. The are apparently military packs that have been discarded
because the spot welds are suspect after they have been dropped. Another example of your
tax dollars at play! </p>
<p>Keith Shaw has a document available from Ken Myer's web site <a href="http://members.gnn.com/KenMyers">http://members.gnn.com/KenMyers</a> that describes
how to assemble battery packs. The article is available as a PDF (Portable Document
Format) file, so you need to have Adobe Acrobat (and some time, because Acrobat is SLOW)
to read it. Rather than try to duplicate that article here, I will add some notes and
list specific materials to use, and where to get them. </p>
<p>One thing you will certainly need is an 80 Watt soldering <i>iron</i>. Note that I said
soldering iron, not soldering gun. A soldering gun typically has a rather small tip size,
and you really need a large flat (chisel) tip to heat up a 1700 cell. The 80 Watt irons
are hard to find; I could not find them at Home Depot, HQ, or Sears, but my local old
fashioned True Value Hardware store has Weller model SP-80 80 Watt irons (red handle,
consumer grade) and replacement tips, too. They cost about $26. I tried using my standard
electronics iron, rated at about 20 watts, and it just would not heat up the cell enough.
The 80 Watt iron made all of difference in the world. </p>
<p>You will also need <i>wiring </i>flux. Again, be careful what you buy. You are doing
electronic wiring, not plumbing, so stay away from acid fluxes. Flux is normally part of
solder, and helps the solder to adhere to many types of surfaces. I think what
it is really doing is reducing the thermal impedance between the iron, solder, and
surface. Sears sells a bottle of 'Liquid Rosin Wiring Flux', number 980003. Sears also
sells large diameter 'Lead-Free Electrical Rosin Core Solder', number 980002. </p>
<p>The cells I bought from Gordy came with paper insulators, which are not really suitable
for our purposes. I removed the paper sleeve and replaced it with clear shrink tubing,
1" diameter. I found that a piece 1.875" long will insulate the top and sides of
a 1700 cell, so I do not need separate top insulators. 3M part number FP301H,
available from Digi-Key as part number FP100C-X-ND, is a heavier gauge shrink tubing than
typically used on cells, but seemed like a good idea as an insulator. I also put
a 0.25" long piece of shrink tubing at the top and bottom of the cells, in place
of the tape that Shaw describes as cell separators. This additional layer of tubing keeps
the cells from actually touching each other. </p>
<p>Properly shrinking the tubing requires a good heat gun. A heat gun intended for
airplane covering may work, but I use an industrial heat gun from Milwaukee, model
8977. It can be adjusted over a large range, and can get VERY hot. </p>
<p>I glue the cells together with PFM, a silicon type adhesive available from Hobby Lobby.
General purpose silicon adhesives probably work too. </p>
<p>The top and bottom surfaces of the cells must be roughened up before the solder will
adhere well. I used a Dremel Moto-Tool and sanding drum. Most of the grinding tools
that come with a Moto-Tool are not suitable for metal. Apply wiring flux to the cell end -
a drop will do - and put the solder and soldering iron tip on to 'tin' the cell. Most of
the flux will boil away, but you should be left with a nice clean blob of solder ready for
soldering on the interconnection braid. </p>
<p>I wire the cells together with 1/4" braid, available from New Creations as part
B-BRAID-3, $1.95 for 3 feet. I put a short piece of 0.25" shrink tubing in the
middle, just in case. Place the braid over the blob of solder left by tinning, and apply
the soldering iron to the braid. More solder may be added once the tinning blob has
melted. </p>
<p>I use Astro Flight Flexible 13 gauge wire, which is available from New Creations, for
all other interconnections. I have not been able to find similar wire available in bulk
from electronics distributors. Most wire strippers will not handle wire this large, so
I gently roll an X-Acto knife around the insulation, and then pull it off. Be careful
not to cut the wire strands. I tape the wires to the ends of the pack as a sort of strain
relief, using 'Heat Shrinkable Tape', available from Radio Shack (gasp!) as number
64-2335, unless they have discontinued it, too. </p>
<p>When you are all done soldering, the flux should be cleaned off the ends of the cells.
A flux cleaner, such as Miller Stephenson MS-990, is the best way to do this. Digi-Key
does not have much of a selection of cleaners, and I am not sure what you will find at
Radio Shack. An electronics supply house may be the best place to find flux remover. </p>
<p>I use Astro Flight connectors. Yes, they are more expensive than the
Sermos/Anderson/Litespeed connectors, but they are polarized for both polarity and type of
connection. If you use them properly, it is impossible to plug a battery into the motor
outputs of your controller, and it is impossible to plug the battery in backwards. People
frequently talk about blowing up motor controllers by plugging something in wrong, and
they are always using Sermos type connectors. I prefer to 'just say no'. </p>
<p>The easiest way to solder the pins for the Astro Flight connectors to the wires is to
pin everything down to a piece of homasote - the same stuff you probably use as a building
board. If you are in fact using your building board, put down a piece of paper towel to
protect it from the flux. Yes, the paper and the homasote can burn at a temperature lower
than the soldering iron tip, but I have never had a problem. With everything held in place
with T pins, it is easy to solder, and you don't have to risk burning your fingertips. </p>
<p>I prefer to test the finished pack before covering it in shrink wrap, just in case I
have to replace a cell. So far, I have not had to replace any. I hook up the pack to my
Robbe Infinity Power Peak charger, and set the charge current to 1A, and the discharge
current to 1.7A (for 1700SCR cells) and cycle it 5 times to a discharge voltage of 6.0V.
The charge and discharge capacity goes up with each cycle, and after 5 cycles it is ready
to be flight tested. </p>
<p>The entire pack should be wrapped in shrink wrap tubing. New Creations has lightweight
shrink tubing in sizes up to 4.5". The actual size required depends on the form
factor of your battery pack. Do not expose this tubing to very high temperatures - it
will shrink easily at low temperatures. </p>
<hr>
<h2>Sources for Electrical/Electronic Materials </h2>
<p>A common question is "Where do I get...." </p>
<p>A very BAD first answer is Radio Shack. They no longer carry much that would be of
interest to an electric flight modeler. </p>
<p>A very GOOD first answer is New Creations R/C. Call Kirk at 409-856-4630 and tell him I
sent you. Kirk can get almost everything, and is willing to MAKE things he cannot get. </p>
<p>If you are looking for electronic devices and materials, the absolutely best source is
Digi-Key at 800-344-4539. Most electronic distributors don't want to deal with small
companies, let alone hobbyists. Digi-Key will send you a $0.02 part if you are willing to
pay the small order charge and shipping charges. Digi-Key carries things like 3M shrink
tubing and Littelfuse Pico fuses. </p>
<hr>
<h2>COPYRIGHT </h2>
<p>The document is copyrighted (c) 1996 by Steven Kranish, and may not be copied or used
in other forms of publication (electronic or paper) without written permission from the
author. </p>
<hr>
<h2>CONTACTS </h2>
<p>If you have any questions, please feel free to contact me at <a href="http://rcgroups.com/shared/nospam.php?u=skranish&d=world.std.com">skranish(at)world.std.com</a>
<p>Welcome to 'From the Lab', the first monthly column on electronics and equipment for
electric flight. This column will discuss motors, motor controllers, batteries, chargers,
radio equipment, measurement instrumentation, and pretty much anything else electrical or
electronic that has an application to electric powered aircraft (and other types of
models, too!) </p>
<p>I have some ideas of what I would like to write about, but I would really
appreciate some feedback from my readers so that I can fly this column in a direction that
you would like it to go. </p>
<hr>
<p><font size="4"><b>Introducing the Columnist</b></font> </p>
<p>My name is Steve Kranish. I grew up in the Washington DC area (I'm from Chevy Chase,
and you're not!), where I was a member of DCRC. I tried to build a few Comet kits when I
was quite young, but my first successful flying models were the model rockets I started to
fly in about 1966. I became involved in RC a few years later, when I purchased a
second-hand Testors pulse system. I don't think I ever successfully flew anything with
pulse gear, but I did try for quite a while, and still have a box of Rand galloping ghost
actuators, Ace pulse actuators, Benterts, and Albins. If you know what those are, well,
you have been at this as long as I have. My first 'real' radio was a Royal 70 Series
purchased as a kit in about 1971. Just for perspective, that radio cost over $200 in 1971
dollars, as a KIT! An entry level new car cost about $2000 in those days, so the
equivalent today would be $800 to $1000. It was NOT a cheap hobby back then! </p>
<p>In the early '70s I flew a variety of model types, and was fortunate enough to meet the
editor of American Aircraft Modeler (AAM), which was based in Washington at the time. I
built a number of models for reviews, which allowed me to try some model types that I
could not otherwise afford. I built a number of ARFs (hey, they were free!) including some
.60 size pattern planes, but eventually drifted into sailplanes. While I was a freshman in
college, I built a Graupner Hi-Fly for a magazine review. Although nominally a sailplane,
the Hi-Fly came with complete instructions for conversion to electric, which was a real
novelty in those days. The electric equipment did not come with the review model, so mine
was built and flown as a sailplane. I still have the model, and it may yet get an electric
setup similar to that shown in the plans - twin pusher Speed 400s with gearboxes, with the
motors mounted at the wing trailing edge. </p>
<p>My work for AAM actually did include building some of the earliest electric airplanes,
although they were all done for the magazine and I never flew any of them. At the time
electrics seemed very expensive, and I was mostly flying gliders off of high starts. The
most memorable of these electric projects was a Kaos 40 pattern plane, converted to
a twin (tractor) electric, with the motors mounted to the wing leading edge. The
plane was trimmed out to look like a transport - I still have photographs, and will
probably include one in a later column. </p>
<p>My interest in model rockets and RC converged with the 1981 Space Modeling (Model
Rocket) World Championships, where I was an alternate to the US team. Try to imagine an 8
ounce vehicle, with 4 ounces of rocket motor, 2 oz of airframe, and 2 oz of radio.
Climbout is vertical, to about 1000 feet in 10 seconds or so. </p>
<p>I drifted out of modeling for a number of years, but never discarded any of my
equipment or planes. The arrival of my son started a 'second childhood' and after flying a
very old Airtronics Square Soar for a few months, I bought a Graupner Elektro-UHU kit.
Actually, I bought all (3) of the electric and sailplane kits at the local hobby store,
because they knew they were never going to sell them. (Typical brain-dead hobby shop that
just sells .40 size trainers.) I built the UHU in about a month, and have been firmly
hooked ever since. </p>
<p>Most of my current flying is at local schoolyards, so electric is the only way to go.
The big fields where I used to use a high start now have buildings on them, anyway.
I frequently fly on the athletic fields that adjoin the center where both of my children
go for day care. At 7:45 AM, no one is there, and since I don't make any noise, no one
seems to mind. The fields are close cropped grass, and the only obstacles are soccer goals
and trash cans. (The UHU has scored one point so far.) </p>
<p>My early interest in RC provided me with a direction for my education and profession. I
have a BS degree in Electrical Engineering from Cornell University. I bounced through
a couple of short lived jobs, including one writing video games, and have been
an engineering consultant for the last 13 years. I presently try to concentrate
on embedded system hardware and software, but I have done everything from Windoze
programming to designing kitchen appliances to digital audio systems used in nuclear power
plant control room training simulators. If you need help on an engineering project, feel
free to contact me. </p>
<p>I had always hoped to work in the RC industry, but while I was getting some experience
as an engineer, the domestic industry went poof. I did get to design the battery
cycler/charger sold by Royal Electronics in the early '80s. I have also designed a very
sophisticated servo tester that can even measure deadband, and a sophisticated
microcontroller based throttle, but neither of those have been commercialized - yet. </p>
<p>I presently live in Beverly, MA, about a 10 minute walk from the Atlantic Ocean in a
house that I share with my lovely wife, two children, ages 1 and 3, (who had better
develop an interest in models), two cats, and more airplanes, kits, and equipment than I
care to think about. </p>
<hr>
<p><font size="4"><b>My Current Airplane Fleet</b></font> </p>
<p>Just to give you an idea of what sorts of electric powered airplanes I am interested
in: </p>
<p>I currently have in flyable condition, or close to it:
<ul>
<li>NSP Neon 400, a Speed 400 class sailplane </li>
<li>Graupner Elektro-UHU, with a Speed 600 direct drive motor </li>
<li>Today's Hobbies Skyvolt, with an Astro Flight 05 </li>
</ul>
<p>In the next few weeks, I should have flying:
<ul>
<li>Griggs Model's Rocket, a Speed 400 class pylon racer </li>
</ul>
<p>My projects for the next year or so include (in New England, we have a real building
season)
<ul>
<li>Great Planes Spectra (I already have a Spirit, so I will just re-use the wing), probably
with a geared Speed 600 </li>
<li>Bridi EZ-1 2Meter Glider, converted to electric </li>
<li>another Griggs Rocket </li>
<li>Midway Models Commander Old Timer </li>
<li>an Elektro-UHU derivative with a larger foam wing </li>
</ul>
<p>I actually have a LOT of other kits and planned projects, but this is about all I can
reasonably expect to tackle in the next year. </p>
<hr>
<h2>My Current Interests </h2>
<p>I am primarily interested in electric sailplanes. My recent experience with the Skyvolt
has convinced me (again) that I am just not an airplane type. Somehow, 5 minutes of
erratic, sloppy aerobatics per flight just doesn't do it for me. What else is there
to do? It does not have the power for touch-and-goes off grass, and it runs down the
battery too fast to justify flying slow circles. With a sailplane, the same challenge is
always present: how long can I stay in the air? In still air I can get 16 to 17
minutes with the Neon, so there is more air time and less ground time. </p>
<p>I have a long term interest in nicad battery capacity measurement, dating from my
design work on a Cycler/Charger for Royal Electronics. This is a topic I will definitely
write about, and I may yet design some commercial products for this area. </p>
<p>I am also interested in motor controllers - they are REALLY throttles, but more on that
in a future column. I have a very good design running on the bench, pending some decisions
about what exactly I should do with it. It may yet appear as a product, but at the
minimum allows me to write about controllers with a full understanding of how they work,
and what sort of tradeoffs are made in their design. </p>
<hr>
<h2>Reader Survey </h2>
<p>I am really writing this column for you, the reader. Unfortunately, I do not currently
know who my readers are, what there interests are, or what their level of technical
expertise is. </p>
<p>If you would like to be part of a reader survey, please copy this section of the column
into an email message, and email your response <i>directly to me </i>(NOT TO THE EFLIGHT
LIST) <a href="http://rcgroups.com/shared/nospam.php?u=skranish&d=world.std.com">skranish(at)world.std.com</a>. </p>
<p>How long have you been flying model airplanes? </p>
<p>How long have you been flying electric airplanes? </p>
<p>What size airplanes are you flying? (Speed 400, Astro 05, Astro 60, converted washing
machine motor?) </p>
<p>What DON'T you like about electric airplanes? </p>
<p>How many flyable planes do you currently have? </p>
<p>Are there any planes you particularly like/liked? Any you particularly disliked? </p>
<p>How many NIB kits do you have? How old is the oldest one? (my answers are
embarrassingly large!) </p>
<p>Do you want to see any math in this column? Would you prefer that I avoid math
entirely? </p>
<p>What sort of math tools do you prefer: sliderule, calculator, spreadsheet, MathCAD,
canned program, finger counting? </p>
<p>Do you know what amperes and volts are? Can you explain the difference? (yes or no will
do, I KNOW the difference) </p>
<p>Do you want to see software code as part of this column? Schematics? </p>
<hr>
<h2>Future Columns </h2>
<p>I would like this column to contain material of interest to the reader. Here are a
few proposed column topics:
<ul>
<li>What is wrong with BEC, and what can we do about it? </li>
<li>Cell Impedances: why the published specs are wrong, and what you REALLY should know </li>
<li>Battery Capacity: how to measure it, what affects it, and what it all means </li>
<li>System Impedances: connector and wire differences and realities </li>
<li>What REALLY limits the capabilities of a motor controller and BEC </li>
<li>Measuring motor and prop performance - the tools you REALLY need </li>
<li>Why Airplane motor controls are so different from car and boat controllers </li>
<li>Converting an inexpensive timed charger to peak detection </li>
<li>Selecting an appropriate drive train - It all depends on what you want to do with it! </li>
<li>Airplane Building Tools - What works, what doesn't, and what you can't live without </li>
</ul>
<p>If there are other topics you would like to see, or some of the above that you DON'T
want to see, please email your response <i>directly to me </i>(NOT TO THE EFLIGHT LIST) <a href="http://rcgroups.com/shared/nospam.php?u=skranish&d=world.std.com">skranish(at)world.std.com</a> </p>
<hr>
<h2>Wiring Your Own Battery Packs </h2>
<p>Nicad battery packs can be a major expense for an electric flight modeler, especially
if you build a lot of different types of models, and each requires a different size or
form factor battery pack. One way to save money is to assemble packs yourself, especially
if can buy appropriate cells second hand. </p>
<p>Gordy Stahl in Louisville, KY at 502-491-5001 sells used Sanyo (and some Panasonic)
1000SCR, 1400SCR, and 1700SCR cells for about $2 each. The cells are either individual
cells or spot welded packs. The are apparently military packs that have been discarded
because the spot welds are suspect after they have been dropped. Another example of your
tax dollars at play! </p>
<p>Keith Shaw has a document available from Ken Myer's web site <a href="http://members.gnn.com/KenMyers">http://members.gnn.com/KenMyers</a> that describes
how to assemble battery packs. The article is available as a PDF (Portable Document
Format) file, so you need to have Adobe Acrobat (and some time, because Acrobat is SLOW)
to read it. Rather than try to duplicate that article here, I will add some notes and
list specific materials to use, and where to get them. </p>
<p>One thing you will certainly need is an 80 Watt soldering <i>iron</i>. Note that I said
soldering iron, not soldering gun. A soldering gun typically has a rather small tip size,
and you really need a large flat (chisel) tip to heat up a 1700 cell. The 80 Watt irons
are hard to find; I could not find them at Home Depot, HQ, or Sears, but my local old
fashioned True Value Hardware store has Weller model SP-80 80 Watt irons (red handle,
consumer grade) and replacement tips, too. They cost about $26. I tried using my standard
electronics iron, rated at about 20 watts, and it just would not heat up the cell enough.
The 80 Watt iron made all of difference in the world. </p>
<p>You will also need <i>wiring </i>flux. Again, be careful what you buy. You are doing
electronic wiring, not plumbing, so stay away from acid fluxes. Flux is normally part of
solder, and helps the solder to adhere to many types of surfaces. I think what
it is really doing is reducing the thermal impedance between the iron, solder, and
surface. Sears sells a bottle of 'Liquid Rosin Wiring Flux', number 980003. Sears also
sells large diameter 'Lead-Free Electrical Rosin Core Solder', number 980002. </p>
<p>The cells I bought from Gordy came with paper insulators, which are not really suitable
for our purposes. I removed the paper sleeve and replaced it with clear shrink tubing,
1" diameter. I found that a piece 1.875" long will insulate the top and sides of
a 1700 cell, so I do not need separate top insulators. 3M part number FP301H,
available from Digi-Key as part number FP100C-X-ND, is a heavier gauge shrink tubing than
typically used on cells, but seemed like a good idea as an insulator. I also put
a 0.25" long piece of shrink tubing at the top and bottom of the cells, in place
of the tape that Shaw describes as cell separators. This additional layer of tubing keeps
the cells from actually touching each other. </p>
<p>Properly shrinking the tubing requires a good heat gun. A heat gun intended for
airplane covering may work, but I use an industrial heat gun from Milwaukee, model
8977. It can be adjusted over a large range, and can get VERY hot. </p>
<p>I glue the cells together with PFM, a silicon type adhesive available from Hobby Lobby.
General purpose silicon adhesives probably work too. </p>
<p>The top and bottom surfaces of the cells must be roughened up before the solder will
adhere well. I used a Dremel Moto-Tool and sanding drum. Most of the grinding tools
that come with a Moto-Tool are not suitable for metal. Apply wiring flux to the cell end -
a drop will do - and put the solder and soldering iron tip on to 'tin' the cell. Most of
the flux will boil away, but you should be left with a nice clean blob of solder ready for
soldering on the interconnection braid. </p>
<p>I wire the cells together with 1/4" braid, available from New Creations as part
B-BRAID-3, $1.95 for 3 feet. I put a short piece of 0.25" shrink tubing in the
middle, just in case. Place the braid over the blob of solder left by tinning, and apply
the soldering iron to the braid. More solder may be added once the tinning blob has
melted. </p>
<p>I use Astro Flight Flexible 13 gauge wire, which is available from New Creations, for
all other interconnections. I have not been able to find similar wire available in bulk
from electronics distributors. Most wire strippers will not handle wire this large, so
I gently roll an X-Acto knife around the insulation, and then pull it off. Be careful
not to cut the wire strands. I tape the wires to the ends of the pack as a sort of strain
relief, using 'Heat Shrinkable Tape', available from Radio Shack (gasp!) as number
64-2335, unless they have discontinued it, too. </p>
<p>When you are all done soldering, the flux should be cleaned off the ends of the cells.
A flux cleaner, such as Miller Stephenson MS-990, is the best way to do this. Digi-Key
does not have much of a selection of cleaners, and I am not sure what you will find at
Radio Shack. An electronics supply house may be the best place to find flux remover. </p>
<p>I use Astro Flight connectors. Yes, they are more expensive than the
Sermos/Anderson/Litespeed connectors, but they are polarized for both polarity and type of
connection. If you use them properly, it is impossible to plug a battery into the motor
outputs of your controller, and it is impossible to plug the battery in backwards. People
frequently talk about blowing up motor controllers by plugging something in wrong, and
they are always using Sermos type connectors. I prefer to 'just say no'. </p>
<p>The easiest way to solder the pins for the Astro Flight connectors to the wires is to
pin everything down to a piece of homasote - the same stuff you probably use as a building
board. If you are in fact using your building board, put down a piece of paper towel to
protect it from the flux. Yes, the paper and the homasote can burn at a temperature lower
than the soldering iron tip, but I have never had a problem. With everything held in place
with T pins, it is easy to solder, and you don't have to risk burning your fingertips. </p>
<p>I prefer to test the finished pack before covering it in shrink wrap, just in case I
have to replace a cell. So far, I have not had to replace any. I hook up the pack to my
Robbe Infinity Power Peak charger, and set the charge current to 1A, and the discharge
current to 1.7A (for 1700SCR cells) and cycle it 5 times to a discharge voltage of 6.0V.
The charge and discharge capacity goes up with each cycle, and after 5 cycles it is ready
to be flight tested. </p>
<p>The entire pack should be wrapped in shrink wrap tubing. New Creations has lightweight
shrink tubing in sizes up to 4.5". The actual size required depends on the form
factor of your battery pack. Do not expose this tubing to very high temperatures - it
will shrink easily at low temperatures. </p>
<hr>
<h2>Sources for Electrical/Electronic Materials </h2>
<p>A common question is "Where do I get...." </p>
<p>A very BAD first answer is Radio Shack. They no longer carry much that would be of
interest to an electric flight modeler. </p>
<p>A very GOOD first answer is New Creations R/C. Call Kirk at 409-856-4630 and tell him I
sent you. Kirk can get almost everything, and is willing to MAKE things he cannot get. </p>
<p>If you are looking for electronic devices and materials, the absolutely best source is
Digi-Key at 800-344-4539. Most electronic distributors don't want to deal with small
companies, let alone hobbyists. Digi-Key will send you a $0.02 part if you are willing to
pay the small order charge and shipping charges. Digi-Key carries things like 3M shrink
tubing and Littelfuse Pico fuses. </p>
<hr>
<h2>COPYRIGHT </h2>
<p>The document is copyrighted (c) 1996 by Steven Kranish, and may not be copied or used
in other forms of publication (electronic or paper) without written permission from the
author. </p>
<hr>
<h2>CONTACTS </h2>
<p>If you have any questions, please feel free to contact me at <a href="http://rcgroups.com/shared/nospam.php?u=skranish&d=world.std.com">skranish(at)world.std.com</a>