Radio Control Electrics - 2004/05

126 MODEL AVIATION
THIS COLUMN INCLUDES two meet announcements; reminds
you of one good, long-running E-site; discusses two common reader
issues; and continues the discussion of power-system/radio-noise
issues that I initiated last month.
Bob Afflerback (123 Harrington Cir., Willingboro NJ 08046; Tel.:
[609] 871-8777) called to announce the 2004 Burlington County RC
Club (BCRCC) Electric meet scheduled for Saturday, June 19 at the
BCRCC Hedding Road Flying Field. Bob is the contact man and Tony
Rossi is the contest director.
The BCRCC E-meet is an established affair dating to the late
1980s, and I believe it is the longest-running E-meet in New Jersey.
I’ve attended many throughout the years, and I know this is a low-key,
friendly gathering.
You can get all the details for this year’s meet from Bob, and
do tell him I sent ya! He has been an E-flier for approximately
two decades and has served as the Electrics columnist for Flying
Models magazine for several years in the past.
Rob Kallok ([email protected]) sent an announcement for
the first Jersey Coast Sport Fliers Electric Fly-In, scheduled for
Saturday, July 17, 2004. The site is a large grass strip at Dorbrook Park
in Colts Neck, New Jersey. Flying is scheduled from 10 a.m. until 7
p.m., and Sunday, July 18 is the rain date. You can get more details
from Rob via E-mail or on the club site at www.jcsportfliers.org.
In recent years there has been an explosion of E-power sites on the
Internet, including club-related offerings. One of the longest running
such sites is at http://members.aol.com/kmyersefo.
This page is managed by Ken Myers, who is president of Electric
Flyers Only, Inc.—a Michigan-based E-group. Ken is also the editor of
Ampeer, which is the club’s monthly newsletter and the basis of the
site. He has been doing the editor job forever, it seems, and he displays
a tireless energy in this pursuit.
Bob Kopski, 25 West End Dr., Lansdale PA 19446
RADIO CONTROL ELECTRICS
Spectrum Analyzer display covers all 72-band RC channels (left
to right). No visible RC signals or power-system noise.
The Spectrum Analyzer’s display of ambient RC channels 16, 18,
38, and 55. The motor is not running.
Same as above right, but motor has been turned on and electrical
noise on ESC/receiver cable is visible all over RC band.
Conditions are exactly like those to left, but chokes have been
installed in ESC cable, clearly effecting great control over offending
ESC noise.
The newsletter, which is more similar to a
mini E-magazine, is available to anyone for
$10 per year, and it offers a great deal of Einfo
each month. Typical content includes
reader-contributed discussion of E-products,
technical offerings, some observations from
meets not found elsewhere, and more.
The site archives include several years’
worth of Ampeer articles. For those without
Internet access, Ken’s address is 1911
Bradshaw Ct., Walled Lake MI 48390 (Tel.:
[248] 669-8124). I assure you that it’s worth
your while to get in touch.
Two frequently encountered reader issues
are requests for article copies and photo
submissions for this column. I am unable to
effortlessly supply article copies, and since I
hate to say “no” to readers on any issue, I ask
that you not ask me for them! Article copies
are available from AMA at a low cost, and
that is your best route. You can also access
AMA’s archives online, but that seems to
work best with a high-speed connection.
I do like to receive reader photos, and I’m
often (but not always) able to include some in
this monthly column. I typically submit
ordinary 4 x 6-inch color glossies (such as
those herein), but sometimes smaller prints
work well too. Please do not write on the back
of your photos, and be sure to turn off the
camera time/date stamp.
MA cannot work with printouts from
digital cameras—no matter how good they
look. On one occasion I received some readerprinted
pictures that looked so good I did not
realize they were not “real” photographs. I
sent ’em to MA along with some monthly
column stuff. They did not work! End of
story!
In last month’s column I discussed a
methodology for easily checking powersystem
noise effects in the shop. I promised
continuing information this month,
including receiver behavioral specifics I’ve
observed.
What might power-system “noise” look
like? For my purposes I set up an eight-cell
brushless, sensorless power system within
some bench fixturing. This fixturing is
shown with the metal shielding covers
removed for viewing.
The right side of the compartmented
enclosure houses the motor, battery, and ESC.
The ESC cable goes through the separating
wall to the left side. This side houses an
inductive link from this cable to a coaxial
port, a stub antenna input to the same port,
and a local “servo driver” RC pulse generator.
The latter is powered from the ESC BEC and
is used to operate the ESC/motor combo via a
front-panel control knob.
The purpose of this fixturing is to observe,
in a controlled and repeatable fashion, any
noise present on an ESC/receiver cable. This
May 2004 127
Shown is an overview of the test fixturing used for the ESC noise tests. The shield
covers have been removed to show components inside.
particular setup includes a known “noisy”
(i.e., radio-interfering) ESC for illustrative
purposes. In use, the mentioned coaxial
output port is cabled to a Spectrum Analyzer
(SA).
The SA used here is automatically
sweeping (tuning) from 72.0 MHz to 73.0
MHz. As such, it is “looking” at our complete
RC band. That is, it can display any radiofrequency
(RF) signal activity on any and all
of our RC channels—simultaneously. You
can think of the SA as a sort of “visual radio.”
The horizontal scale represents a radio dial,
with each major grid representing five of our
50 channels of operation.
As in the preceding, the SA input is looselinked
to the ESC cable and to a stub antenna.
As such, any RF signals present in the ESC
cable and in the local air can be seen. That is,
any signals that fall within our RC band of
interest that may be present on this cable as
noise, or in the local air as “real” RC signals,
can be seen on the SA display. “Noise” is
generally defined as any undesired signal. For
the technically interested, the vertical scale is
a logarithmic display having a 10 decibel/Div
scale factor.
Another photo is just such a picture; in
128 MODEL AVIATION
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this case it shows nothing present. The lownoise
baseline represents ambient signal
conditions viewed at the full sensitivity
available with the SA, just like what a
receiver antenna may “see” in a no-signal,
RF-quiet environment. In this case this
baseline noise is simply that which occurs
naturally in electronics; i.e., “thermal noise,”
and is so small that it has no effect on an RC
system.
A different photo shows a display that
might typify active flightline conditions.
Specifically, I turned on four nearby
transmitters—one each on channels 16, 18,
38, and 55. The four vertical lines represent
these real RC signals. Keep in mind that here
the SA is acting as an RC receiver; the big
difference is that the SA tunes and displays
every RC channel all the time.
A photo shows the added presence of
power-system noise actually picked up off the
ESC-receiver cable. Here the power system
was run up using the built-in servo driver
circuit of the fixturing. The four ambient RC
signals remain in place as markers. It should
be clear that this power-system noise covers
all of our RC spots!
Thus should any controlling RC
transmitter signal ever fade in flight (it will!),
electrical noise present could easily get into
the RC receiver as dominant (and possibly
problematic) interference. Depending on how
weak the real signal, how strong the ESC
noise, and how the specific receiver would
react, the airplane could then glitch
accordingly. Any response ranging from
nothing to a major consequence is possible.
To complete this picture story, one of the
photos is the same as another—but with
chokes installed in the ESC-receiver cable! In
this case, as is usually the case, the “chokes”
method is highly effective in reducing or
eliminating most power-system noise
problems. (In rare instances, chokes are
ineffective because the noise problem may not
be associated with the ESC-receiver cable.)
Longtime readers may recognize some of
this presentation as similar to one in the May
1995 column. I’ve been pursuing this general
topic for many years. What is new here is a
more highly refined and repeatable test
methodology combined with vastly improved
SA resources. That is, I am now doing what
I’ve been doing much better!
As part of this recent effort, I have also
studied the effects of ESC-related noise on
various receivers. In particular, I have six
different receiver types on channel 38, and I
tried each on the bench in conjunction with the
same eight-cell brushless motor, controller,
and transmitter. These receivers include an
FMA Extreme, an FMA Fortress, a Futaba
127DF, a Futaba 148DF, a Hitec 555, and a
FMA Quantum 6. (The order has meaning as
follows.)
Each receiver was powered by the ESC
BEC, and servos were connected to the
elevator and rudder outputs—on each side of
the throttle slot. I proceeded as described in
detail last month, running up the throttle some
and then turning off the transmitter to observe
resulting servo and motor behavior.
What I found was eye-opening. Depending
on the specific receiver in use, servo glitching
and/or erratic motor behavior would variably
occur upon loss of the transmitter signal. That
is, when the transmitter signal went away, with
the motor running, the power-system noise
would “take over” the receiver and result in
glitching that would last varying amounts of
time until the motor would finally stop.
For this particular set of conditions, with
this specific motor/controller, the FMA
Extreme was the best of all receivers tested. It
has been discontinued, and I have no FMA M5
(the replacement receiver) to try in its place.
With the Extreme, the servos did not twitch
at all upon transmitter shutdown, and the
motor shutdown was smooth and uneventful. It
was the only receiver to display this solid
behavior. The Extreme was so good that I had
no way to observe the effect of chokes; there
was nothing to improve! The performance was
impressive!
Each of the other five receivers had
associated servo twitching and/or motor
misbehavior upon transmitter shutdown—at
least to some degree. Response ranged from a
little to a lot in the order that I listed the
receivers. I then tried chokes in the ESCreceiver
cable with each and, as expected,
offered total (or nearly) improvement.
ESCs (especially microprocessor-based
ones) can “pump” offending power-system
electrical noise into your airborne receiver via
the ESC-receiver cable; this offending noise
can adversely manifest, especially during those
times of in-air signal nulls (signal dropouts);
the resulting system behavior (glitching or not)
can depend heavily on the response of the
particular receiver; and chokes usually help
with this.
Please include an SASE with any inquiry for
which you’d like a reply. Everyone so doing
does get one.
Have a great Electri-flyin’ springtime,
everyone. MA