Electrics - 2006/08

Electric highlights of the 2006 Weak Signals (Toledo) Show
August 2006 109
Electrics Greg Gimlick | [email protected]
Also included in this column:
• Data acquisition systems
from Eagle Tree Systems
• Improving your model the
easy way
AstroFlight’s new 120 direct-drive motor for large models spins 15- to 22-inch propellers and
runs on six- to 12-cell Lithium packs. R: Unique propeller adapter machined to perfectly fit
the APC-Es.
Greg’s Air Hog Aero Ace made the rounds
at the PERF event at Toledo. A $30, 3/4-
ounce airplane system was put in anyone’s
hands who wanted to try. John Kauk photo.
Castle Creations’ prototype Phoenix SHV 130 super-high-voltage ESC will handle up to 20s
(maybe more) input voltage (90). “Low current” version is roughly 130 amps continuous (11
kilowatts, or roughly 15 horsepower). “High current” version could be as high as 220 amps
continuous (18.5 kilowatts, or roughly 24 horsepower).
IN THE LAST column I got into some
technical things and building motors isn’t
for everyone, so this month I’ll cover a
wide variety of topics including Toledo
impressions, data acquisition, and random
thoughts of an “old guard” electric-power
modeler.
TOLEDO WEAK Signals Show: The big
question I’m asked when I return is
always, What’s the one highlight of the
show this year?
Although there were some cool things
again, the highlight had to be the pure
quantity of electric stuff available. Almost
every booth had something for the
electric-power flier, and the proliferation
of tiny indoor electrics was a marvel. Just
as impressive was the advancement in
Giant Scale Electrics, as evidenced by
visits to AstroFlight and Castle Creations
booths.
Last year I whined loudly about the
demise of the indoor fly the Perrysburg
Electric River Flyers (PERF) group used
to put on at Bowling Green State
University during Toledo Show weekend.
It was swallowed up by the more
commercial indoor Electric Tournament
of Champions, and the regular ol’ indoor
fliers with micro-sized airplanes were left
without a place to have fun.
Big kudos to the PERF group for
coming up with a gym near downtown
that allowed us to have a great evening of
relaxed micro indoor flying. We had a
blast, and even my .75-ounce Air Hogs
Aero Ace spent most of the night in the
air. This is a great little airplane, and I
think half the people in attendance must
have taken a turn at the sticks.
Thank you, PERF, for putting on this
event!
Eagle Tree Systems—Data Acquisition
for the Rest of Us: What the heck does
that mean?
For a few years there have been inflight
data-acquisition systems for
08sig4.QXD 6/23/06 10:21 AM Page 109remotely controlled vehicles, but you
needed to bring your whole wallet if you
wanted one. I’ve lusted for one to use with
product reviews so I could give real-time
results with accurate numbers when I
evaluated a system in an airplane.
In the past I’ve done the math and the
projected performance calculations with
the help of ElectriCalc and MotoCalc. It’s
been useful and pretty accurate, but
nothing can really tell you what’s going
on unless you can get the data during the
flight. Eagle Tree Systems to the rescue!
The company’s Seagull Pro system is the
ultimate but is beyond the reach of many
modelers, and quite frankly most don’t
need something that is that expandable. If
you’re a competitor, it’s certainly the way
to go, but the average flier will be more
than happy with the new MicroPower
system. Following are the MicroPower’s
key features.
• Logs pack current to 100 amps and
voltage to 45.
• Software computes wattage, mAh, etc.,
for complete electric-flight data.
• Accepts optional inexpensive sensors for
temperature and rpm (magnetic or
optical).
• Supports simultaneous temperature and
rpm sensors or two temperature sensors.
• Weighs approximately 0.5 ounce (17
grams). Version with wire leads weighs
slightly more.
• Supports USB Live Mode, which lets
you see what is happening in the model
live on the bench, on your PC.
• Has adjustable logging rate (one to 0
samples per second) and lossless data
compression for long log times.
110 MODEL AVIATION
Eagle Tree Systems’ MicroPower dataacquisition
system is the answer to many
questions for modelers. It’s small in size and
easy to use. Screen capture of one of the author’s Gee Bee tests from the MicroPower system.
• Comes with state-of-the-art Windows
virtual playback display and graphing.
• Features powerful graphing software
with advanced charting features, such as
amps vs. volts.
• Has Internet-updatable firmware. As
Eagle Tree adds new features or (heaven
forbid) has a firmware bug, the update is
just a download away! There is no need to
ship hardware back and forth.
I grabbed this list off of the Web site so
I wouldn’t have to type it myself, and
every bit of it is true to the letter. I’ve used
my system several times, and it’s
extremely helpful.
Would I like to have airspeed? Sure I
would, and it’s available on the Seagull
system if I want to spend that much. We
want to know what our current, voltage,
and rpm is doing, along with some
temperature information, and every bit of
that is available on the $70 MicroPower
system. The additional sensors you might
want are inexpensive, ranging from $10 to
$15.
The system also features a “live mode,”
so if you’re working in the shop you can
read everything on your computer screen
while it’s happening. I normally just use
the memory buffer of the unit and
download it to my laptop after my model
lands, but the live feature is neat when
you’re trying different propellers and
gearing combinations because you can get
the static info instantly.
There are several options for sampling
rates, which will extend the record time of
the unit while reducing the number of
readings per second.
If you’re still wondering if having a
data system is worthwhile, let me tell you
a story. While setting up my 1/4-scale Gee
Bee R-2 I ran all the static numbers and
found the setup that worked well.
I called Pete Peterson at Model
Electronics Corporation (www.model
electronicscorp.com/) and bought a Merlin
2000 motor geared 5.5:1 with an MEC
Monster Gearbox, Castle Creations HV-85
controller, and two “Twenty” PolyQuest
4S-3700 Li-Poly packs in series. This
setup spins an APC-E 20 x 10 propeller at
5,500 rpm and draws approximately 43
amps, giving me roughly 90 watts per
pound.
Every now and then I heard a strange
sound from the Gee Bee, and each time I
checked things out everything seemed fine.
It was momentary, but clearly a change in
sound.
I mounted the MicroPower system with
the optical rpm sensor reading the
propeller and temperature sensor on the
motor. The system automatically logs the
voltage and current. I ran the system until I
heard the sound and it recovered, and then
I repeated the run. This gave me enough
data to see whatever was happening twice.
I downloaded the data, which is a
simple matter of hooking the special USB
cable to the unit and my laptop. When you
run the data playback, you can see the
gauges and numeric readings in real time
as the clock runs, and you can pause it at
any time. My two runs accumulated almost
five minutes of data, and the buffer wasn’t
nearly full.
08sig4.QXD 6/23/06 10:47 AM Page 110As I watched the data run, I suddenly
saw the rpm drop and the voltage rise while
the current dropped. It recovered within a
couple seconds and ran along fine until it
suddenly did it again. There were my two
data points for the sound I heard!
What does it tell me? My guess was that
something was allowing the propeller,
pinion, or spur gear to slip momentarily.
This would account for the sudden drop in
rpm which was reading from the propeller
and the reduction of load that would cause
the battery voltage to increase.
I had checked the propeller for tightness
before and all seemed fine, but this time I
tore into the system knowing one of them
was slipping, so I paid close attention as I
disassembled it.
It turned out that when I fitted the
propeller bushing it protruded out the back
of the propeller a tiny bit, and that affected
its tightness under loads. It could slip and
then be okay again. I trimmed the bushing
and made sure all was tight, and then I
reran the tests. All was fine.
Having a preliminary data log gives me
a base point to keep on file. When I think
something is not the way it used to be, I can
easily run another test and compare it to the
first. This tells me if anything is changing
and just what it is.
I highly recommend the little
MicroPower if you’re going to do Electrics
seriously. It’s light and quick to install; I
can hook it up on one of my airplanes in
approximately 10 minutes anytime I want
data.
Improving Your Model the Easy Way:
I’ve been accused of being “old guard”
because I’ve been flying Electrics for quite
awhile and remember when accomplishing
an aerobatic four-minute flight at the KRC
Electric Fun Fly was an achievement.
Those days are long gone, but the desire
to improve my setups continues. I’ll bet I
get three or four E-mails each month with
the following type of question:
“I’m flying an electric [model] with a
cobalt motor, [a certain] controller, with 10
1700 mAh Ni-Cd cells and love it. The
performance is fine, but I’d like more
duration, so I guess I have to bite the bullet
and buy a new brushless motor, controller,
and a Li-Poly pack.
“Since it’s going to be so expensive, I’m
looking for advice. Can you help me?”
The key is the sentence about being happy
with the performance but wanting more
duration. There’s nothing wrong with the new
brushless-motor setups and Li-Poly batteries. If
you’re happy with performance and want only
more duration, why not look at your batteries
first?
Replace your sub-C Ni-Cds with something
such as GP-3700 NiMH cells, and suddenly
you’ve doubled your battery capacity and
increased duration. If you really want the Li-
Poly packs, you can have them too without
replacing the whole system.Get a Li-Poly pack that will handle the
current you’re drawing and either replace the
controller or go the more economical route of
getting an Automatic Cell Detect, Low
Voltage Cutoff Device (item AVC1AIR)
from FMA Direct (www.fma
direct.com). This will allow your old
controller to use the new Li-Poly packs, and
since you’re going to lighten the model with
the Li-Polys, you’ll increase your duration
even more because it won’t require as much
power.
Don’t throw away good equipment if
you’re happy with the way your airplane is
flying. Some of the cheap brushless motors
flooding the market are no more efficient than
a quality brushed motor such as the ones
AstroFlight has produced for years. Spend
your money carefully and wisely, but don’t
get caught up in “upgrade fever”—unless you
just feel like it. MA