Micro-Flying - 2010/11

ONE OF THE
biggest challenges
we face in
constructing and
designing a
micromodel is
keeping the weight
to a minimum. With
advances in battery
technology and
ultralightweight receivers and construction materials, we can build
models weighing only a few grams or less.
One of the last obstacles we face is a lightweight power source.
Fortunately several modelers are making great progress in designing
single-phase micro brushless motors that weigh mere milligrams and
consume less current than standard brushed motors.
These single-phase brushless motors are relatively simple in
design. They consist of a coil, magnet, motor shaft, bearings, and
brushless DC motor driver such as the Allegro A1442.
The A1442 uses a single Hall element sensor to detect the
rotational position of the magnet. This small chip measures only 1.5
x 2 mm, weighs 3.8 milligrams, and can handle up to 400 mA. Wire
size, coil ohms, magnet size, air gap, and chip location are variables
that affect the power the motor can produce.
The first model that I witnessed flying with a single-phase
brushless motor was my friend Robert Guillot’s incredible 3.8-inchspan
Ord Hume 7. I was blown away by the scale performance of
the little aircraft. He made every part on the 1.1-gram airplane
except for the receiver and battery.
The tiny motor was the key to the aircraft’s success. It weighs
only 175 milligrams with a 3 x 2 mm magnet and a coil wound to 38
ohms. It can fly the model for 2-3 minutes on an 8 mAh Li-Poly
cell.
Robert used Martin Newell’s Rabbit receiver with Hip Hop
programming, which is also a major contributing factor to the
success of this model. Robert has since built several brushless
motors with improved performance.
November 2010 97
Joe Malinchak Micro-Flying | [email protected]
Also included in this column:
• 1/72-scale MiG-15 with EDF
power
Ultramicro brushless motors
Dan Baird constructed this amazingly tiny 0.5mm motor, to see
how small of a power plant he could build.
Robert Guillot built
these micro singlephase
brushless
motors. The larger
one weighs 320
milligrams, draws 120
mA at 3.6 volts, and
puts out 1.5 grams of
static thrust. The
smaller motor draws
120 mA at 3.6 volts
and puts out .75
gram of thrust—
perfect for use on an
ultramicro model.
The author and Stefan Gasparin collaborated on this 1/72-scale MiG-
15. Joe designed the model and Stefan designed the amazing EDF
20. It might be the world’s first 1/72-scale EDF-powered jet!
With 4 grams of thrust, Joe had high hopes of success for the MiG;
however, he had to fly it without the nose section because of the
small intake area. He has to make a few changes in the design, and
then it should be great.
Another modeler who is doing an
excellent job on the design and
construction of these new brushless motors
is Dan Baird. He has been working hard to
build a motor with power equal to or more
than the 4mm, 13-ohm pager motor. This
interests me, because that type of motor
can power models such as my 1/72-scale
designs.
Dan designed a motor that uses a
2.5mm magnet and an 18-ohm coil. The
power plant is close to the 4mm pager’s
performance, with much less current draw
and one-third of the weight.
For fun, Dan wanted to see how small
of a motor he could build. He ended up
building an incredibly tiny 0.5mm motor
with an 8mm propeller.
I think his best achievement to date is
his work on a 6-inch-span, four-channel
Ultimate biplane. Dan built everything on
it except the fourchannel
Rabbit
receiver. The
model is
constructed from
Durobatics foam
and weighs 2.25
grams with a 10
mAh Li-Poly cell.
For power, Dan
designed a geared,
brushless motor
that weighs only
0.42 gram.
For those who
are interested in
building motors,
Dan has a
wonderful thread
regarding his
motors and
information about
his Ultimate
biplane. See the
“Sources” listing
for the Web site address.
If you are interested in trying a motor
of this type but do not want to make your
own, Nick Leichty of Micro Flier Radio
has added them to his site. Nick also sells
the Rabbit receiver, coils, and many other
great products for your next micro project.
1/72-Scale MiG-15 EDF: In the last column
I mentioned the progress I had made on my
1909 military Wright Flyer and included
photos. I had planned to have it flying by
now, but I got sidetracked again.
My friend, Stefan Gasparin, started
working on some great new electric-ductedfan
(EDF) motor designs. He sent me a
beautiful prototype EDF 30 that I plan to use
on a 1/32-scale F-86.
After discussing plans for my F-86
design, I mentioned that it would be great if
we could go smaller to power a 1/72-scale jet.
He wrote back that
it was a crazy idea. I
reported that his
little 400-milligram
brushless outrunner
that I used in my
1/72-scale Corsair
has plenty of power and suggested that he
design a version for a little EDF.
So this joint project began. I knew we
needed a model with a wide fuselage for
an efficient EDF unit. I choose the MiG-
15, because the fuselage is 20mm at its
widest part in 1/72 scale.
I started designing the MiG, and
Stefan went to work on the 20mm EDF.
He ended up designing a beautiful unit
that used the G09UL 1000 motor.
The complete EDF 20 weighs 1.65
grams. It was slightly heavier than I had
hoped, but it showed great potential.
Static thrust is 4 grams on the Fullriver
30 mAh cell. My MiG-15 is constructed
from Durobatics foam, has a 51/2-inch
span, and weighs .94 gram empty.
I had to keep the weight of everything
to a minimum. I use a four-channel
Rabbit receiver that Martin Newell made
for me, which has pulse-width
modulation output for a brushless ESC. I
used only one coil for rudder control.
The completed MiG-15 weighed 4.84
grams, so I knew it had a good chance of
flying; however, the initial attempt was
unsuccessful. My first thought was that
the intake was too small, and I was right
on the money.
I tried the model without the nose
cone and it flew. That was only a few
hours before I completed this column on
August 10, 2010.
The flight was short—approximately
a minute—but it was an exhilarating
minute. It might be the world’s first 1/72-
scale jet model to fly. I plan to redesign
it with a larger intake duct and maybe a
little more wing area. MA
Sources:
Dan Baird’s build thread:
www.westknoxrc.com
Micro Flier Radio
(941) 377-9808
http://microflierradio.com
Gasparin CO2 Motors
+420 323 603 00
www.gasparin.cz
98 MODEL AVIATION
Stefan Gasparin’s EDF 20 unit weighs 1.65 grams and uses his
G09UL 1000 motor. It measures 20 x 16 mm and puts out 4
grams of thrust on the Fullriver 30 mAh Li-Poly cell.
Dan Baird constructed everything except the receiver on this 6-inchspan,
four-channel Ultimate biplane. Made from Durobatics foam, it
weighs 2.25 grams and features a geared .42-gram, single-phase
brushless motor.
Robert Guillot’s incredible Ord-Hume has a 3.8-inch span and
weighs 1.1 grams. He built its single-phase brushless motor that can
fly for up to 3 minutes on an 8 mAh Li-Poly cell.