This column announces a meet, lists
two Electric Connection Service readers,
shares more information about the Universal
Slow Charger (USC), and discusses
mounting small servos.
colin mcKinley, an active E-enthusiast
from “way back,” wrote to tell me about the
(North Carolina) Triad Electric Weekend
scheduled for May 5-6.
This meet is hosted by two clubs: the
RAMS on May 5 and the Winston-Salem
Radio Control Club Inc. on May 6. Each club
will use its own field for the day specified, but
both fields are available Friday, and both have
primitive camping and generators.
The RAMS Contest Director (CD) is
Nat Shepard ([704] 633-1788) and the
W-SRCC CD is Colin McKinley ([336]
924-5890). The meet(s) coordinator is
John Mountjoy ([336] 722-7609; E-mail:
[email protected])—another longestablished
E-aeromodeler and former
co-author of an Electric Column in RC
Report magazine.
Each day has lots of flying activity planned,
beginning with “continuous flying.” Other fun
activities include Biggest Model, Smallest
Model, Best Original, AULD (All-Up/Last
Down), and Wingo Racing, to name a few.
These activities vary during the two
days, so get the meet mailer from someone
listed above. And do tell ’em Bob sent ya!
Two readers have requested a listing in this
column’s exclusive Electric Connection
Service. The idea is to help those in Eisolated
areas connect with other locals of
kindred interest. This service is open to
everyone—just write me and ask.
Craig Mitchell (8383 Twin Lakes Dr. S.,
Mobile AL 36695; Tel.: [334] 633-6875; Email:
[email protected]) is retired and has
the time and interest to pursue E-aeromodeling,
and he would like to hook up with others in his
immediate area to share the fun. He says he
would like to be able to fly closer to home.
Anyone in Craig’s area who is reading
this, please get in touch with him. (Gee,
maybe this is a new club in the making!)
Bob Signorello (RD#3 Box 17-C,
Meshoppen PA 18630-9203; Tel.: [570]
833-4674) is just starting in E-power, and he
very much wants some face-to-face
opportunities with other E-modelers.
I’m asking and encouraging others in the
area to get in touch with Bob so everyone can
have more E-fun! And tell ’em “Bob sent ya!”
Reader interest in the USC continues to be
high, and this may become the most-built
hobby-related electronics project I’ve shared
throughout the years.
One photo this month shows how one
reader feels about the USC. Blair West (Saline
MI) initially wrote to ask about a difficulty he
was having, and to let me know that if he got it
working okay he’d build two more as gifts.
We corresponded, and got things working
fine. The photo tells the rest of the story: now
Blair, his son, and his son-in-law are fully
equipped with dual USCs! Those are nice
Christmas presents, wouldn’t you say?
This prompts me to repeat my standing
invitation to anyone with questions or
problems: just write, and I’ll do everything
necessary to get your USC up and
running—no matter what.
One reader, who was among the first to
build the charger and get it into routine use,
recently wrote to tell me that half of his dual
had stopped working. We corresponded rather
extensively, but this time that approach did
not work. So I invited him to send me the
problematic Control Circuit board.
As it turned out, this assembly had a
component failure that I consider a fluke. Once
Bob Kopski, 25 West End Dr., Lansdale PA 19446
RADIO CONTROL ELECTRICS
Blair West’s trio of Universal Slow Chargers. Two were for gifts. Blair, his son, and his
son-in-law run RC boats—the USC is useful for everything!
FMA S-60 servo mounted in Elipstik using method described in text. Plastic tape wrap
on servo, tape on wood floor, auto trim double-stick foam tape in between.
102 M ODEL AVIATION
104 M ODEL AVIATION
identified, it proved easy to fix and I was able
to return his circuit very quickly.
Although this was a “first,” I’m willing
to give it a hands-on shot if we can’t crack
your problem with correspondence.
Another reader had a special charging
need, and he customized his dual USC
version to include a switchable range on
one of the two outputs.
As presented, USC has fully adjustable 0-
500 mA output current ranges, with options to
modify the range for lesser values.
The design also includes an optional,
readily available 0-500 mA meter to read the
dialed current. But the 500 mA adjustment
range and the 500 mA meter scale would not
allow easy setting and reading of very low
currents, as are sometimes needed.
A 50 mA pack, as might be used in an
indoor/park flyer, would be slowcharged
at roughly 5 mA, and this small
current would be very hard to set with a
0-500 mA knob range and very hard to
read on the 500 mA meter; it would
barely move the needle.
To get around this, reader Al Flesher
(Baltimore MD) made a modification as
suggested in the construction article.
Using component values given, he
incorporated a range switch on one of the
output adjustment knobs so this same control
can cover the original 0-500 mA range or a
reduced 0-50 mA range. But although this
selection allows the easy setting of low-value
currents, it does not improve the meter
readability for them.
To solve the matter, Al simply calibrated
(put markings around) the dial for the lower
range, and now he sets the knob to those
values as desired.
Overall, Al did a beautiful job of
constructing and labeling his dual USC. I
wanted to share the picture he sent, but it
was digital and not reproducible here. (For
reproduction, you must send good-quality
conventional photographs—with no
writing on the back!)
While on the USC subject, following are
some additional reader-driven points.
The USC circuitry is not “reverse
battery” protected. Protection against
such a mishap would have required
considerable additional circuitry, and I
deemed it not worth the cost and
complexity.
Therefore, you (and I) must always
make sure that a battery polarity is correct.
One easy way to do this is to make
customized interconnecting cables that
can’t be connected wrong.
If you do happen to hook up
“backward,” the USC will proceed to
charge your pack “backward”—never
good for the pack, and maybe not good
for the USC. The latter is the case if the
pack is roughly 20 cells or more, and is
partially charged when you hook it up
backward.
Be forewarned: it’s necessary to connect
your battery with the proper polarity!
The USC design is highly efficient, and
this means it generates very little internal
heat, no matter the battery being charged
or the charge current.
Nevertheless, it’s necessary to heat-sinkmount
some transistors to the metal cases to
aid in keeping things cool. One of these is
Q1 in the Advanced Power Supply option,
and the other is Q1 in each Control Circuit.
Both transistors are TO-220 packages; i.e.,
they have metal mounting tabs.
Some readers got confused about
mounting these parts. The mounting tab is
also (one of two) collector connections, and
as such, must be electrically insulated from
the metal charger case.
However, this mounting tab is also the
main thermal path for cooling the
transistor, so it must be thermally
connected to the case when called for.
The “electrically insulated” and “thermal
mounted” dual requirement is met with the
mounting kit specified. The kit includes a
conventional 4-40 screw, lock washer, and
nut. It also includes a “large” rectangular,
thin, flat mica electrical insulator/thermal
conductor washer and an insulating eyelet.
This kit is used beginning with a 1⁄8-
inch-diameter hole drilled in the metal
case, taking care not to distort the metal
surface; keep it flat.
It is critically important that there are no
surrounding burrs, so smooth the metal
surface well. (Even a tiny burr on the case
metalwork can cause an electrical failure—if
not immediately, then in time).
Insert the screw from outside the case,
putting the mica washer over the part
protruding inside the case. Slip the transistor
tab in place flat against the mica. Put the
insulating eyelet over the screw so that it
enters the hole in the transistor tab.
Follow up with the split lockwasher
against the shoulder of the eyelet, then add the
nut and tighten the whole works. It is not
necessary to use a thermal grease in the USC.
Now the transistor is mechanically
mounted, thermally mounted, and
electrically insulated from the metal case
and metal mounting hardware. It’s wise to
verify that there is no electrical connection
between the transistor mounting tab and
the case with an Ohmmeter.
Tiny servos, as used in the highly popular RC
park flyers, can very easily be mounted with
double-stick foam tape. The thinner tape for
adhering external trim mouldings, which is sold
in auto-part stores, works very well—too well!
That kind of tape can be very hard to remove
from the servo or the mounting surface. The
latter is usually balsa, and attempting to remove
the servo and tape usually just tears at the wood.
Following are some tips.
First use some ordinary plastic tape on or
as a wraparound for the servo body. This
forms an intermediate layer that is much
easier to remove later. The double-stick tape
adheres to this plastic-tape “interlayer.”
If you already have some of the tenacious
double-stick tape on servos, you can remove it
by peeling as much as possible off the servo
case. Then moisten a paper towel with some
turpentine-based (oil) paint thinner, and rub
away at the sticky residue. This takes some
work, but it does the job.
Finish up with a rubbing alcohol-moistened
tissue to remove the oily thinner residue. Do
not use lacquer-based thinners or solvents!
The plastic tape interface also works well
on the wood mounting surface. Start by treating
the wood with some rubbed-on Ambroid or
similar glue and let it dry. (Epoxy and CyA
[cyanoacrylate] do not work as well for me.)
Smooth any hardened wood “fuzz” with
finishing paper and stick the plastic tape in place.
Then comes the servo/double-stick foam
tape combo, and presto! You have a foam
tape-mounted servo that can be removed
without destroying the servo or the surface
to which it’s mounted!
so ends this early-springtime column, as I
prepare to go shovel some snow! Please
include an SASE with any correspondence
for which you’d like a reply.
Happy and many springtime or anytime
E-landings, everyone. MA
Shu Gee’s (Sun City AZ) original Gamma 2E: 75 ounces, 500 sq. in., Astro 15G, 12 1.4s,
11 x 7.5 prop, 0.65 thrust-to-weight ratio. Based on earlier “60” wet design.
