January 2010 95
Red Scholefield | redscho@The Battery Clinic bellsouth.net
Also included in this column:
• Lithium-battery use in
transmitters
• Spark-suppression update
• How to toast an AXI
• WMR upgrades to the CBA III
• If it doesn’t feel right, it
probably isn’t!
Findings of electric Old-Timer conversions
This AXI’s motor
windings show the
effect of being stalled.
The windings are
coated for protection,
but overheating will
wear away that
security measure.
Red’s West Mountain Radio CBA
III, set up to test battery packs, is
clean and efficient. He used to
have a lot of equipment to do the
same job.
I HOPE YOU will indulge me as I
address a couple of nonbattery/charger
topics.
In the September column, I lamented
an Old-Timer FF conversion’s squirrely
performance and the flutter problem in a
powered sailplane. Maybe I can stretch it
and claim that getting a model to behave
correctly falls under the topic of safety. So
with apologies to MA’s “Safety Comes
First” columnist Dave Gee, I will share
some letters from readers.
Kerswap comments begin with Will
Greenwood of Warner Robins, Georgia.
“It appears to me that you are trying to
fly a competition free-flight aircraft
outside of the limits of its design.
“The Kerswap was designed to
maximize a 15-second powered climb, in
right turns, shut off the motor, and glide
as long as allowed by the rules. A spiral
climb was found to be much more stable
than a straight climb. Therefore, the spiral
slipstream from the propeller was directed
to strike the left side of the pylon and
force the aircraft to spiral to the right.
“The high wing and rearward centerof-
gravity made the plane try to loop,
while the pylon effect added an upward,
right spiral. This combination turned the
‘loop’ into a climbing corkscrew path of
about one-and-one-half turns before the
motor stopped. The vertical stabilizer,
which was tiny by today’s standards,
allowed the tail of the airplane to ‘skid’ to
the right which kept the nose pointed
upward during the climb.
“My own successes in converting
competition free flights to RC required
enlarging the vertical stabilizer (some
modelers call it a ‘rudder’) and switching
rudder rates on the transmitter. Some of
these planes required some left rudder
during takeoff. All my high pylon planes
required full-throttle takeoffs. Gradual
takeoffs frequently resulted in ground
loops.”
Jack Albrecht added:
“You probably are aware that the SAM
R/C assist flyers have been flying them for
quite some time. I have been flying a 630
square inch wing area Lanzo Bomber for
over 20 years in the SAM Limited Motor
Run event as well as the Texaco event.
“The same old Bomber now uses a
Hacker B40 10L +4.4 Gearbox swinging a
15x8E APC propeller and the same 800
mAh pack. Climb is straight up.”
Another Old-Timer, Kenneth Spittler,
has also been adding electric to some of
his vintage FF models, but only after
01sig3.QXD_00MSTRPG.QXD 11/20/09 2:03 PM Page 9596 MODEL AVIATION
fairly extensive modifications such as
moving the wing pylon back and
increasing fin and rudder areas. Recent test
flights at our club with an electrified
Zipper by Lyman Slack showed the same
twitchy tendency as the Kerswap did.
Thanks also to replies from Robert
Hoey, Alex Zobell, and John Juechter, who
sent pictures of their conversions, it
appears that Old-Timer FF is alive and
well, as electric power and radio control
(assist) enable them to be flown in more
restrictive areas.
Howard Chapman wrote in about the
flutter issue, as follows.
“Of all the variables that can lead to the
problem I’ll only get into what probably
applies to your powered glider. Many
years ago we had 12 to 15 Ugly Sticks at
the Sepulveda Basin field. All flew with no
problems in spite of poor building and
poor equipment/linkage setups in many.
“Then they came out with MonoKote
covered Sticks instead of the normal
silk/silkspan with dope. These had aileron
flutter caused by the plastic covering being
stretchy which changed the torsional
resistance of the wing. One ugly cure used
strapping tape in a diagonal crisscross
pattern. The other went old school and
mass balanced the ailerons with lead
weights.
“Many big plane engineers did that way
back when and it’s still the best cure I
have seen over the years, either of these
cures work the same way. They change the
vibration modulus to preclude the aileron
flap speed to not get into a harmonic with
the wing rotational spring rate. Mass
balance doesn’t have to be absolute—just
enough to disrupt the modulus match
causing the problem.
“One of my friend’s pattern ships was
a flapper. When building the second one
of the same I suggested top mounting the
hinges instead of the kit center mount
instructions. The second model didn’t
flap and the hinge change didn’t affect
the flying.”
Jack Page addresses Lithium use in
transmitters. He wrote:
“I have noticed a trend among some of
our fliers to replace their transmitter and
airborne Ni-Cd’s with Li-Polys,
obviously for the additional power and
flight time possible. I think this is a
mistake.
“To my knowledge, none of our radios
have voltage limiting circuits which will
prevent the Li-Poly pack from overdischarging.
This can ruin the pack and
possibly damage the equipment.
The CBA III’s programming screen shows a number of
parameters.
You can test any type of battery with the CBA III. It has many
safety features too.
Left: Red tested a set of transmitter batteries. The CBA III
discharge cycle shows the capacity remaining.
Red learned a simple lesson in power switches. This dissected one
shows the meltdown of insulating components. Something didn’t
feel right, and he should have checked it out.
01sig3.QXD_00MSTRPG.QXD 11/20/09 2:03 PM Page 96January 2010 97
“Electric fliers have some protection
via their ESCs but this protects the
airborne pack only. Wet fliers have no
protection at all.
“And how many times have you
accidentally left your radio turned on after
finishing a day’s flying? That total
discharge could be a disaster. Has anyone
ever made your readers aware of this
potential problem?”
This issue has concerned me since it
emerged. Leave your transmitter on one
time, and you have ruined the battery. Or
worse, the battery could start a fire.
I have a Lithium pack for my
transmitter but use it only as a backup or to
extend my flying time at the field. I
remove it after use, for charging and
storage.
Your flying environment will have
some bearing on what kind of battery you
employ. Li-Poly packs will enhance
daylong sessions at the field. I have asked
Tony Stillman of Radio South if there is an
issue with the voltage, but he assures me
that there is not.
The information, in the September
issue, regarding spark suppression has
some caveats. “DustyIV” posted the
following on the RCGroups forum.
“What happens here is the Castle
Creations ESC by default is set to
automatically count the number of Li-Poly
cells. If a resistor is added on the input to
slowly charge the caps, the auto detect will
grab a count before the charge is complete.
“So let’s say you are using a 4-cell
pack. The auto detect may think it’s a 3-
cell. You can take off and everything
seems fine. Then it shuts the motor off
thinking the voltage is pulled low.
“I checked with Castle Creations and
this is their response: ‘We recommend a
1ohm 5W resistor with our ESCs. A higher
resistance rating can cause issues with the
auto-Lipo detection.’”
For those interested, there is a long
thread on the subject. See the “Sources”
listing for where to find it.
Toasting an AXI: I have been a strong
proponent of AXI motors since they
became available. I have never found one
to fail. But you can make it happen if you
want to badly enough.
Leave the throttle up a bit if you make a
forced landing in high grass. Some ESCs
have a cutout, but under the right
circumstances, it doesn’t happen before the
stalled motor is damaged. You can see the
results in an accompanying photo.
West Mountain Radio’s original CBA II
(Computerized Battery Analyzer) has
established itself as one of the best batterytest
devices in the hobby. Now it has been
replaced with the CBA III (costing
$149.95 for the consumer version), which
has significant new features and its
software update to Version 2.1 (which
works on all CBA units).
As did earlier models, the CBA III
works in conjunction with your computer,
plugging into a USB port where it is set up
with a program from the provided CD. It
covers all battery types that we
aeromodelers use and allows you to set the
discharge parameters. Check out the
photos of the setup options and the battery
types served.
The CD that is supplied with the CBA
III has Microsoft Windows WHQLcertified
drivers for Windows 98SE, XP,
Vista 32, and Vista 64. It is also tested and
ready for Windows 7.
The calibration has been tightened, to
typically plus or minus 0.5% from .5 to 40
amps and plus or minus 0.5% throughout
the voltage range. Maximum testing
voltage increased to 55, with voltage
ranges of 0-5, 5-15, and 15-60. The wire
pigtail on the earlier CBA has been
replaced with Anderson Powerpole
connectors.
Dual FETs lower the internal
resistance, allowing regulation of more
than 30 amps down to .9 volt for nickel
cell discharges. They also make it much
Visit the AMA Web site at www.modelaircraft.org.
01sig3.QXD_00MSTRPG.QXD 11/20/09 2:03 PM Page 9798 MODEL AVIATION
more difficult to burn out, with reverse
polarity or loose connections to the battery
and lowering the operating temperatures for
better reliability.
The CBA gives you a clear and concise
story of your batteries’ performance. I
upgraded my transmitter to one of the new
packs made with Sanyo Eneloop cells. I
wanted to see how much flying time I had
after my morning at the field—mostly
thermal hunting with my converted Bird of
Time.
I ran a discharge with the CBA III,
programmed to show minutes rather than
amp-hours, and set for what my transmitter
current drain would be. As you can see in
the provided photo, after more than an hour
of flying, I had enough capacity for much
longer. After a few sessions with a CBA III,
you won’t have to wonder how close you are
to the edge with your battery packs.
And significant other: this would make a
great gift for the aeromodeler in your life.
I use a double-pole toggle switch for my
main power on electrics, wiring across both
sets of poles in parallel. After many flights, I
noticed that the switch didn’t feel right. But
since it was in one of my clunkers, I flew
anyway, only to lose power immediately
after takeoff.
When I retrieved the model, I couldn’t
turn the switch to the off position and found
that one of the solder connections had
melted from the switch. In the following
autopsy, I learned that the plastic bar that
toggles the contacts had given up, making a
high-resistance contact, resulting in
overheating at the switch contacts. In an
accompanying photo, look at the two metal
contact trips removed from the switch
housing and the deformed plastic toggle at
the left.
If it doesn’t feel right, it probably isn’t!
Thanks for the e-mails and letters
addressing my “problems.” I hope I have
solved some of yours in the meantime.
Please note that I have canceled my
membership at RC Universe. If you have
battery questions, I do monitor the battery
and charger forum on RCGroups. MA
Sources:
Jack Page
page-john@att.net
Spark-suppression discussion:
www.rcgroups.com/forums/showthread.ph
p?t=1090782
RC Groups’ battery and charger forum:
www.rcgroups.com/batteries-andchargers-
129
Red Scholefield at the Battery Clinic
12219 NW 9th Ln.
Newberry FL 32669
www.hangtimes.com/redsbatteryclinic.html
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