RADIO CONTROL ELECTRICS - 2004/08

98 MODEL AVIATION
THIS COLUMN includes one meet
announcement, one Electric Connection
Service (ECS), a follow-up to the April/May
“noise” topic, discussion about switches and
their application, and a closing item of note.
Plenny Bates, a longtime reader from the
early 1990s, sent me information about the
Cedar Rapids (Iowa) Sky Hawks Electric
Fun Fly scheduled for August 7-8. Plenny is
the meet CD.
You can find all the details at
www.foxcoins.com/skyhawks/funfly/. If you
don’t have online access, you can call Plenny
at (319) 362-2969. An AMA license is
required to participate in the meet.
Bill Baker (1902 Peter Pan, Norman OK
73072), who is an established aeromodeling
contributor and longtime reader from the late
1980s, asked if this column’s ECS could
assist him.
Bill and others in his area pursue an
interest in E-powered sailplanes, and they are
seeking others to join in this specialty. If this
is of interest to you, get in touch with Bill.
The April and May columns included
information about power-system-induced
radio noise, which brought in reader
comments and queries. Most interest was in
the “chokes” cure that I mentioned in those
columns.
Chokes have been discussed in “how to”
detail several times throughout the years, but
because there is so much current interest,
I’ve rephotographed the detail and offer it
again.
As presented in the April and May
columns, it’s common for power-system
electrical noise to find its way into the
receiver system and manifest as glitching.
One way this happens is via the receiver-
ESC cable; it interconnects the radio and
power systems. As such, it can form a “noise
highway.” The April and May columns
suggested an easy way to test for noise
problems.
There are generally two ways to improve
or even eliminate this adverse condition, one
of which is to use an ESC with an optoisolator
input. This is probably the best you
can do, but you need to get another ESC, and
this approach disallows the use of a BEC.
The second option, which is often nearly as
good, is to use chokes in the receiver-ESC
cable. You can apply this method to any
existing ESC, and it does allow the use of a
BEC.
Both approaches work by “breaking up”
the radio frequency (noise) path between the
Bob Kopski, 25 West End Dr., Lansdale PA 19446
RADIO CONTROL ELECTRICS
Brushless ESCs usually have large capacitors on the input power wires. These can
easily result in destroyed power arming switches. Text has details.
A miniature toggle switch with heavy wires can cold-switch upward of 30 amps. The
small slide type only activates ESC electronics.
Finished CIU and parts to make another. It’s a simple, low-cost problem solver.
08sig4.QXD 5/21/04 12:01 pm Page 98
receiver and the ESC while leaving the two
connected as far as motor control signal
goes. (I discussed this and more in greater
detail in the September 2002 column.)
I have been using the chokes method with
success on six meters and on “72” for more
than a decade. This technique is easy and
low in cost, and it can be used with no
jeopardy to anything of which I’m aware.
If you’ve determined—or even suspect—
that you have electrical noise problems in
your Electric model, consider trying the
chokes approach, as follows. (Some
modelers just put them in as a matter of
course, noise or not!)
The photos detail how to make Choke
Insertion Units (CIUs), in this case with
Futaba connectors, but CIUs can be made for
any radio-connector system, and all that is
needed is a matching aileron extension. (I
usually use a 6-inch extension.)
The chokes—which look like resistors
physically—are 10-microhenry units and are
Mouser Electronics catalog item 542-77F100.
Mouser is nice to do business with. Call (800)
346-6873 or go to www.mouser.com. Each
choke costs approximately 60¢, and you can
place small orders with Mouser without
penalty. Each CIU needs three chokes, so
this is a small investment.
The only other material you need is heatshrink
tubing, such as a Du-Bro assortment
from a local hobby shop.
Begin assembly by cutting the extension
cable and parting and stripping the three
individual wires of each cable half, as
shown. A 3⁄16-inch stripping is about right,
but take care not to cut any strands in the
process. Twist and tin the exposed wire ends.
Slip a 1⁄4-inch length of 1⁄16-inch heatshrink
tubing (Du-Bro blue or equivalent)
over each of the six aileron cable-wire ends.
Slip a 11⁄4-inch length of 1⁄4-inch heat-shrink
tubing (Du-Bro yellow or equivalent) on one
of the cable ends. Trim the choke wires to
roughly 3⁄16 inch, add solder to each, and then
lap-solder the wire ends to the choke wires.
Be sure to connect like wire colors to
each end of the same chokes; make no
mistakes here! And take care not to allow the
shrink tubing to be heated before its time has
come.
After you have made all six solder joints,
inspect them well for connection quality;
your model depends on this. When you are
satisfied, slide the smaller heat-shrink pieces
CIU assembly in progress. Chokes soldered in-line with short lap
joints and heat-shrink tubing ready to insulate all.
Completed CIUs. One has clear heat-shrink cover; one has
opaque Du-Bro tubing. Both use cut aileron extension cables.
August 2004 101
over the solder connections and use a
covering gun to shrink them.
Slide the 1⁄4-inch tubing over the
connections and the chokes, centering it on
this stuff. Bring the heat gun to bear, and
your CIU is finished.
The completed CIU can be connected
(inserted) in-line with the ESC/receiver cable.
I suggest that you replay those test exercises
in the April and May columns (or your field
range test) without the CIU, and then again
with the CIU in place. I’m betting that your
noise problems will be eliminated or greatly
reduced!
Since some have asked, yes, you can just
cut the ESC cable and install the chokes
there. But there is always a chance that noise
conduction in this cable is not the problem
path. The deployable CIU allows easy
confirmation.
If it’s successful, you can leave the CIU in
place or install chokes in the ESC cable. I
prefer the former approach. I routinely carry
a spare CIU in the car; often I can help
someone on the flightline with this easy fix.
A photo of switches includes some that
might be found in RC Electrics. The toggle
switches are the kind I use as arming
switches in brushed power systems. These
are the type—with heavy wiring attached—
that I’d normally employ in systems up to 30
amps. I install these in series with the battery
and ESC input.
The switches shown are my time-proven
favorites: the DPDT (Double Pole Double
Throw), which is ITT Industries/C&K part
7201SYXQE or Digi-Key catalog item
CKN1035-ND (at [800] 344-4539 or
www.digikey.com).
AMA Academy of Model
Aeronautics
ARF Almost Ready to Fly
BEC Battery Eliminator Circuit
CAD computer-aided design
cc cubic centimeter
CD contest director or
compact disc
CG center of gravity
CL Control Line
cm centimeter
cu. in. cubic inch
DT dethermalizer
EPP (foam) expanded polypropylene
ESC Electronic Speed Control
FAI Fédération Aéronautique
Internationale
FCC Federal Communications
Commission
FF Free Flight
LCD Liquid Crystal Display
LE leading edge
LED light-emitting diode
Li-Poly Lithium Polymer
mA milliamperes
MA Model Aviation
mAh milliampere-hours
MHz megahertz
mm millimeter
Nats AMA Nationals
Ni-Cd Nickel Cadmium
NiMH Nickel Metal Hydride
RC Radio Control
rpm revolutions per minute
RTF Ready to Fly
SASE self-addressed, stamped
envelope
SIG Special Interest Group
TE trailing edge
ModelAviation’s
Frequently Used Abbreviations/Acronyms
______
______
ts!
e
08sig4.QXD 5/21/04 12:02 pm Page 101
102 MODEL AVIATION
These switches are not cheap, but they
are good! (I do not recommend RadioShack
switches.) I use both poles in parallel—this
with a wire overlap soldered to both
terminal sets.
Many readers ask how such little
switches—perhaps rated at a few amps—
can be used in much higher-current power
systems. The answer is that they are not
used to switch “live” circuits; the ESC does
that. That is, with the throttle off, arming
the system by turning the switch on results
in no current flow. This “cold” condition
permits successful application of a lowcurrent
switch in this higher-current job.
But why?
Switch contacts take the most abuse
when energizing/de-energizing “hot”
circuits. With the throttle in the off
position, flipping the arming switch is
almost like flipping it connected to nothing.
You can do this a zillion times with
impunity. There is no make or break arcing
taking place at the contacts, so they hold up
well.
Once closed, and the ESC is activated,
these contacts are easily capable of
carrying much higher currents. I’ve been
using them this way for decades. After
many years and many models, I’ve never
had a failure of this quality part—until
recently, when I “blew” one. The switch
was instantly internally destroyed. This
came as a surprise, given the long-standing
success, but I quickly learned why.
In the preceding I referred to the
application to brushed systems. The one I
blew was in a brushless application. Unlike
most brushed controllers, most brushless
ESCs have huge capacitors on the power
input leads. Not only are these high-value
capacitors, but they are low equivalent
series resistance (ESR) capacitors.
The large value capacitance and low
ESR combine to make these parts
extremely low impedance at switch closure.
In effect, it is like momentarily closing the
switch on a dead short—whether the
throttle is off or not—and the associated
brief but intense “sparking and arcing” fries
the contacts.
I still use my favorite toggle switches in
my brushed applications, but no switches in
my brushless applications. I’d like to, but I
can’t find any that are capable of handling
hundreds of amps of transient current that
are still small enough to fly!
Much against my established
preference, and to my dislike, I’m forced to
use power-system connectors as switches
in brushless systems. The “sparking and
arcing” upon connection closure still takes
place. But I’ve found (as guided by the
observation/suggestion of Bernard Cawley)
that Anderson Power Poles do this well.
That is because the initial contact is at
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08sig4.QXD 5/21/04 12:02 pm Page 102
August 2004 103
the tips of the contacts and not at the final
contact mating surface. The latter is
farther back on the metal fingers, so it
avoids that initial contact abuse. Thus the
“sparking and arcing” does not put the
important part of the connector contacts
in jeopardy. So until something better
comes along, that’s how I’m doing it.
By contrast, the small ESC-associated
slide switch shown is not a “power”
switch. One glaring clue is its light-gauge
wires, which are much too small to
handle much motor current. Its purpose is
only to arm/disarm the ESC electronics;
i.e., to permit or not permit the throttle
electronics to work.
Turning it off does not remove power
from the ESC circuits, which continue to
draw a small current from the motor pack.
This is what I discussed in the April
column as the culprit in allowing packs to
drain to their death! If this is the only
kind of switch in your power system, be
sure to disconnect the battery when
you’re finished flying!
This is a special column. I’m writing this
a few days after receiving my copy of the
May issue of MA and roughly a month
after receiving my copy of the April
issue. This particular month has set a
record; I received 37 reader letters in
reaction to the April discussion of an
apparent design/manufacturing problem
in the aging ACE Pro 810/RCD Platinum
AM receivers.
This somewhat alien topic brought in
the largest, quickest reader reaction ever!
I’m truly gratified that so many found
interest and help in a topic that I
reluctantly included in this column.
So ends one more column and concludes
20 years of my association with MA and
you. Thank you all for giving me this
great opportunity to “fly” with you! Ain’t
Electrics great?
Please include an SASE with any
correspondence for which you’d like a
reply. Everyone so doing does get one.
Many happy summertime E-landings,
everyone. MA
08sig4.QXD 5/21/04 12:03 pm Page 103