Radio Control Electrics - 2004/04

April 2004 129
THIS COLUMN INCLUDES an Electric Connection Service
(ECS) request, a Lithium-Polymer (Li-Poly) battery advisory, a
receiver-problem advisory, an application for the Astro 05
brushless motor, a simple test for power-system noise effects,
and one potential product announcement!
Ron Evans (1262 Elizabeth St. #204, Denver CO 80206) wrote
to tell me about electric activity in his area. A local group flies a
wide variety of Electrics in a Denver-area sports complex and is
expecting to soon formalize as an AMA chartered club: the
Rocky Mountain Electric Flyers.
As club secretary, Ron is extending an invitation to those of
E-interest in the area to get in touch with him. You are also
invited to visit the flying site every Sunday (weather permitting)
at the soccer complex west of Kipling Street and 58th Avenue in
Arvada. Flying is from 9 a.m. to 2 p.m. And when you visit, do
be sure to tell the guys that Bob sent ya!
As a reminder to all, this column’s exclusive ECS service is
available to all individuals and groups looking for E-others
nearby. Just send me the pertinent info, and I’ll include it in an
upcoming column—free for the asking!
Li-Poly batteries for motor power are getting popular, and some
related problems are becoming common. Li-Poly charging and
discharging protocol is critical, and it is important to treat both
with great care. Some modelers have inadvertently ruined their
Li-Poly packs without knowing it by leaving them connected
following flight.
Some Electronic Speed Controls (ESCs) are equipped with
prewired on-off switches. The switches I’ve seen only control
the electronic operation of the ESC and do not disconnect power
to it. These switches are easy to recognize; they are small and
have light-gauge wire connecting them. They are not “power”
switches.
An ESC so implemented can still draw standby current with
the control switch off and eventually drain the motor battery.
Unfortunately, draining a Li-Poly too far immediately destroys
it. In fact, draining a Ni-Cd or NiMH pack way down—although
perhaps not immediately obviously destructive—does eventually
impair the pack and in time can seriously degrade its
performance.
Therefore, it’s extremely important to disconnect a Li-Poly
(or any other) battery at the end of a flight. Think of it as a
simple act to save big bucks!
The January 2004 column described my good experiences with
some new AstroFlight 05 geared brushless motors, and the
March column added to the topic. The January column described
how I resurrected my 13-year-old Skyvolt and how equipping it
with the new product produced a whole new airplane.
Regrettably, this original “cover girl” Skyvolt is no more. I
identified an intermittent receiver as the crash-causing culprit. It
was an old but honorable ACE Pro 810—an AM receiver
operating on six meters. I found the problem in the receiver, and
it turned out to be the result of a design/manufacturing flaw. I
then examined three similar receivers and found the same latent
condition.
Specifically, there is a polarized tantalum timing capacitor
installed backward (reversed polarity) on the board, and in time
this causes the capacitor to degrade into intermittent operation.
I realize that this is an “old” product, but if you are using the
Bob Kopski, 25 West End Dr., Lansdale PA 19446
RADIO CONTROL ELECTRICS
The beginnings of the Rocky Mountain Electric Flyers in Arvada
CO. See text for how to hook up with this group.
Circa 1975-1980 Astro can 05 system raises question of meaning
of “05,” given today’s more powerful Astro 05 brushless.
The 390-square-inch Caliph was pressed into service as test bed
for Astro two-turn 05 brushless, sensorless system.
130 MODEL AVIATION
ACE Pro 810 AM receiver, you may encounter this situation. If
you are interested, write to me and I’ll expand on the specifics,
including how to fix it. Meanwhile, I’m flying my repaired
receivers with renewed, solid performance. (The same problem
occurs with the same-design, same-vintage RCD Platinum
receiver.)
As previously described, the Skyvolt was equipped with a twoturn
AstroFlight geared brushless, sensorless motor on eight
2400s. The resulting performance, with a 10 x 5E propeller, was
spectacular—vastly superior to any earlier power system used in
that model.
The January column suggested that this power system could
make new airplanes out of similar-sized models from that earlier
time, such as the Mirage, the PT Electric, the AeroLectric, and
others. Having lost the Skyvolt, I went digging through my
inventory.
One photo shows my old 48-inch Davey Systems Caliph. I
discussed this model in detail in the July 1987 column (yes—
nearly 17 years ago!), so it’s even older than the Skyvolt. I
rescued the Caliph from a heap in my attic, washed it, and sized it
up for the Astro two-turn. Basically I installed the same system
that was in the Skyvolt, and, as before, this installation produced a
gratifying “whole new airplane.” But there is more.
Realizing that many similar airplanes from that era were
intended to be flown with “can” motors on six or seven cells, I
wanted to find out how this reduced cell count would affect the
flight results. I substituted a seven-pack and, with the same
propeller (10 x 5E), flew a satisfactory Caliph—one that well
outperformed any previous power installation.
Going further, I installed a six-cell pack, and on the bench I
determined that a 10 x 6 Master Airscrew Electric Wood propeller
would probably be a better choice. The Caliph now weighs 41
ounces—down from 48-49 ounces in 1987. I’ve flown this
combination several times, and this lower-weight, higher-power,
longer-duration four-channel Electric is much better than with any
earlier power system.
Again, consider the Astro brushless in airplanes of old (or new,
for that matter). If you have some similar-sized six- and sevencell
Electrics gathering dust, render them new with a simple
power-system change. I’m confident that you will be impressed
and happy with your completely revitalized aging Electric.
This column has discussed power-system noise problems and
fixes many times throughout the years. Many readers have used
my oft-mentioned “chokes” solution to such problems. More
recently I’ve had more experience with this noise subject and
want to share it here. First, a review.
Within any power system there are several potential radiointerfering
noise sources. These include speed controls (especially
microprocessor-based ones) and, in the case of brushed motors,
sparking at the brush/commutator interface. Related adverse radio
effects can cover unflyable all the way down to slight or no
reduced-range noise levels. In general, higher-power systems are
more likely to be problematic.
The classic power-system noise test is to do a normal walking
radio range test and then do it again with the motor running at
partial throttle (typically the worst case). Marginal control may
then occur closer to the transmitter (i.e., less range) with partial
throttle compared to with the motor off—a sure sign of powersystem
noise influence.
I usually only accept a small range reduction—a few steps,
perhaps—depending on the distance baseline for the test. Of
course, opinion varies, and I know some who would accept half
range—a performance degradation that would make me quit for
the day! In principle, I see no need to give up any range.
Signal conditions at the receiver can vary tremendously
throughout a flight. Not only is the airborne receiving antenna
(thus received signal strength) all over the place, but there are
naturally occurring signal nulls, or “dropouts,” in signal in the air
over almost any field. These can even occur close-in and so are
unrelated to radio range per se.
As in the preceding, it’s during conditions of weak signal at
the receiver that noise can manifest—usually as surface jitter
and/or erratic motor operation. The latter is often the first noticed
effect. Think of your power system as a potential interfering noise
generator, always right with your airplane, just waiting to invade
the nearby receiver when the intended controlling signal is
weakened or absent.
I have been experimenting with a methodology to check for
such effects without having to do a range test for noise on the
field. This can be done with all equipment “on the bench” or with
everything installed in a finished airplane at home. As such, it’s a
big help in verifying new installations or working on problematic
ones. However, it’s only appropriate with radios otherwise known
to have proper flight range in the first place.
You can try this approach in your shop. Turn everything on
and verify your surface controls. Run up the motor over the
throttle range to assure proper operation, and then return the
throttle stick to full off. If everything seems okay, turn off the
transmitter power switch and observe the surface and motor
reaction.
Many radio systems will display a small surface “twitch” at
this time, and some may display a short motor indication as well.
Repeat this several times to firmly establish what is “normal” for
your system so you know what to expect hereafter. If the motor
starts momentarily but then erratically continues on a bit, you
have probably already found a noise problem!
The common “twitch” often experienced when turning a
transmitter off seems to be a characteristic behavior of the
receiver. I have examined several receivers in the same setup and
have experienced a range of resulting behaviors. I’ll share what I
have on this next month.
When you’re confident about what to expect following
shutdown of your transmitter, repower the transmitter, reverify
normal surface operation, and then advance the throttle until the
motor is running steady at roughly idle level. Switch the
transmitter power off, and observe the control surfaces and motor
behavior again. Look for the same patterned response established
previously.
If the earlier pattern was for some characteristic “twitch” of
the surfaces and/or minor motor disturbance, you should expect
the same thing now. But if there are now lingering or exaggerated
surface jitters and/or erratic motor operation, you almost certainly
have noise influence. Except for the most minor or rarely
occurring effects, this is unacceptable to me and generally
curable.
The next step is to repeat this regimen, but with a more
advanced throttle setting—say approximately halfway, and then
again at full throttle. Everything else in the preceding descriptions
remains the same.
Do each test several times to establish or verify pattern
New geared motor nested in “V” block, clamped with “Golden
Rod” inners and #2 draw screws. Motor-mounting scheme
introduced in July 1987 column became popular.
behavior. The goal is to have the same
effects when the transmitter signal
disappears no matter the motor power level,
as would happen if the motor were always
off. All of this is an at-home attempt to
simulate an in-air severe signal reduction or
loss.
Some ESCs do have a designed-in delay
that permits the motor to continue running
(smoothly!) for a short time upon momentary
loss or corruption of signal. This, then,
would be a “normal” or expected behavior
for such an ESC. In this case, a quicker or
longer and/or erratic motor shutdown would
be a departure from normal. (I had one
experience where the motor would not stop
at all!)
As best as I can tell so far, this
methodology may be a bit more stringent
than the classic field test. That may only be
the case for some radios, but it is okay by
me. I’m continuing to pursue this stuff and
will expand on it if and when there is more to
offer. In the next column I’ll review some
related “dos” and “don’ts” and cures for
common power-system noise problems.
Great News! The October 2003 column
described what I believe is a much-needed
electric product: ESCs with BECs (Battery
Eliminator Circuits) of “switch mode” design
so that even “high cell count” power systems
could shed the normal radio-system battery.
At least one such ESC design is “in the
mill,” but I have no more to offer at this
time. Stay tuned. I can’t wait, because such a
product is long overdue!
So ends another column. Here’s wishing
you many happy springtime (or anytime!) Elandings!
Please do enclose a self-addressed,
stamped envelope with any correspondence
for which you’d like a reply. Everyone so
doing does get one. MA
April 2004 131