Electrics - 2012/02

94 MODEL AVIATION
entered electrics 20 years ago. He tolerates
my silly questions and puts things in plain
language for me.
The main question I want to address is:
Is it better to lengthen the wires from the
battery to the ESC or to lengthen the wires
from the ESC to the motor? The online
forums are full of ideas, opinions,
conjecture, and debate about this question.
Forums have done more to confuse the
issue than to answer the question.
Let me give the simple answer first. It is
better to lengthen the wires from the ESC
to the motor and keep the battery wires as
short as possible. That’s it, plain and
simple.
The debate centers on resistance and
inductance. Some
argue that by using
a larger-gauge wire,
resistance is
reduced, making the
longer battery wires
acceptable. What
that doesn’t address
is the increased
inductance it
causes. The
proponents of
lengthening the battery wires say that can
be overcome by adding additional
capacitors to the front of the ESC. This is
not a fix, but a patch.
The ESC already comes with capacitors
installed as determined by the designer for
its intended application. Without specific
knowledge about current and how good the
flyback diodes are, along with the
switching speed of, the voltage rating of,
and types of Field-Effect Transistors
(FETs), you’re grasping at straws. Even if
you do know those things, you’ll need to
do a lot of math to figure out the
appropriate caps to add.
Here is a quote from Bob Boucher on
the topic of which wire to lengthen:
Also included in this column:
• AR Drone
ESC wiring
Electrics Greg Gimlick | [email protected]
Top: Keeping the battery wires short is the best option.
Note the short run between motor and battery to the
ESC in my Fw 190.
Above: My Waco employs a 12S LiPo pack and Astro Mega
motor and draws nearly 100 amps, so wire length is critical in
keeping everything running happily.
Left: The author’s AR.Drone rests on the shop floor between
sorties.
TAKING OFF: I hope you have a warm
shop and are spending time in it getting
your creations ready to fly when the
weather breaks. Don’t forget to share
photos and information so I can pass it on
to others.
Do you have a cool way of doing
something that might be of interest? I’m
always looking for tips and tricks to share,
so don’t be shy. Email me with the details
and photos.
Let’s continue down the path of figuring
out problems and look at some more things
that can give you nightmares if you’re not
careful.
ESC Wiring: I’m going to start with my
usual disclaimer: I am not an electrical
engineer! This information is meant for the
everyday flier who is trying to keep from
ruining his or her equipment. It is gleaned
from information I received from engineers
who design speed controls for various
manufacturers. I’ve tried to keep it accurate
and put it in layman’s terms.
Many thanks to Doug Ingraham for
helping me work through this debate. Doug
has been designing some of the top speed
controls and chargers on the market since I
02sig3.QXD_00MSTRPG.QXD 12/16/11 1:56 PM Page 94February 2012 95
Bob is comparing inductance in the
motor-to-ESC wire to inductance in the
ESC-to-battery wire.
Bob is better known as “AstroBob,”
former owner of AstroFlight and holder of a
patent on electric flight. He knows his stuff,
so I listen.
Books could be written about the science
behind this, but I think you get the idea. If
it’s possible, always lengthen the wires
from the motor to the ESC. The best
possible solution, of course, is to keep all
wires as short as possible, but we know
that’s not always easy when you’re doing
that special Scale project.
Thanks to the people at AstroFlight,
Castle Creations, Schulze Elektronik, and
Doug Ingraham for the help.
AR.Drone: I hardly
know where to start
with this little gem. I
don’t know of it’s a
“toy,” or a
“quadricopter,” or a
“First Person View
(FPV) vehicle,” or
the coolest school
science project ever.
This is a gold mine
for science and math
teachers, along with
computer science
teachers, industrial
arts teachers, etc.
Based on the
open-source Linux
operating system,
with developer
support from Parrot,
the potential is
endless. I’ve
mentioned this flying
machine before, but I’m seeing more of
them popping up in local hobby shops and
hearing about them from readers, so I
guess the following is growing. Because
it’s the dead of winter, I thought maybe a
look at this would be interesting because
you can fly it around in your shop.
The AR.Drone is a quadricopter
designed by Parrot that uses a Wi-Fi
connection to your iPhone, iPad, or iPod
Touch for control. If you don’t have an
Apple product, don’t despair. There are
applications—apps—to support other
products as well. The cool thing about this
is that it also gives you the ability to fly
using FPV technology and I’ve done that
right inside my shop.
In case you’re curious, AR. is short for
augmented reality. Think heads-up
displays, where you’re integrating reality
with virtual input. Remember the movie
The Terminator? His display was
augmented reality. Flying the system in a
full-scale Apache is the same thing. The
pilot flies the helicopter using the
monocle displaying the Forward-Looking
Infrared (FLIR) image with all the flight
and weapons systems superimposed. This
is super-cool stuff for a hobbyist’s
machine.
Here’s a look at the specifications:
Embedded Computer System:
• ARM9 468 MHz
• DDR 128 MB at 200 MHz
• Wi-Fi b/g
• USB high speed
• Linux OS
Inertial Guidance Systems with Mems:
• 3-axes accelerometer
• 2-axes gyrometer
• 1-axis yaw precision gyrometer
Above top: This iPad screen capture shows
the author using the MatrixFlight HD
program to fly the AR.Drone.
Above: A screen capture of his iPad
displays the author flying his AR.Drone
with the free AR.FreeFlight software.
Right: The author flying the Drone with
the iPhone, while the Drone looks back
at him taking a photo of him flying, while
his brother- in- law takes a photo …
confused yet?
“I will repeat the answer previously given.
I hope you heed some sound advice based
on theory and practice.
“1. Wire resistance may rob you of a bit
of power but will not destroy your speed
control or motor.
“2. Wire inductance will not damage
your motor, nor will you be able to detect
any effect even with 100 feet of wire.
“3. Wire inductance will kill the
MOSFETs [metal-oxide semiconductor
field-effect transistor] in your control and
may even blow the caps.
“I’ve been a design engineer and
manufacturer of motors and controls for
over 30 years. You must keep battery wires
as short as practical. Short means 1 foot or
less, brushed or brushless, [it] makes no
difference.”
02sig3.QXD_00MSTRPG.QXD 12/16/11 1:56 PM Page 95Specifications:
• Running speed: 5 meters per second/18
kilometers per hour (16.4 feet per
second/11.2 miles per hour)
• Weight:
- 380 grams with outdoor hull (13.4
ounces)
- 420 grams with indoor hull (14.82
ounces)
• Flying time: approximately 12 minutes
• Quadricopter constructed of carbon fiber
and high-resistance PA66 plastic
The device can be flown using one of
several available apps, but the “official”
one is called AR.FreeFlight. The others are
variations that add extra capabilities or
features and more are being developed all
the time. There have been apps developed
that will allow for video capture, as well as
flying it from computers instead of
iPhones.
I’m not quite the geek I once wanted to
be, so I haven’t ventured into flying it with
my computer—yet. There are
approximately one dozen apps available for
the iPhone, and I keep exploring more and
more. I need a neighbor with one so we can
dogfight!
The AR.Drone comes with two bodies. I
recommend using the big foam indoor body
for indoor flying. It protects the rotors from
strikes against anything and if you’re like
me, you’ll bump into a few things while
learning the ropes.
I’ve also climbed too high in the garage
and had one of my hanging airplane’s gears
stick down into the rotors. That causes the
safety feature to kick in and stop all the
rotors (this saves little fingers) and it
crashed 10 feet to the floor. Amazingly,
there has been no damage because of the
big foam body. This is a kid-friendly
machine.
Camera views can be switched from
forward to down-looking cameras with the
touch of a finger. All the apps pretty much
work the same with controls. The left
button activates the accelerometer function
of the iPad or iPhone, and as you tip the
phone, the Drone will fly in that direction.
The button on the right allows you to rotate
the drone around its vertical axis and adjust
altitude.
If you get yourself into trouble, let it go
and it will stabilize itself into a solid hover.
If you wonder how stabile it is, just give
the big foam body a push with your finger
and watch it recover. This is amazing.
What is even more amazing is that
something this sophisticated can be sold for
approximately $300!
I’m impressed with this Drone and as
applications grow, it will become
increasingly capable. There are forums and
websites dedicated to the full spectrum of
its development and use. The Tamiya-type
battery connector is cheap and safe, but as
we’ve seen in the electric flight world
throughout the years, it’s inefficient.
Any modification to the aircraft will
void your warranty, but I chose to replace
my connectors with Anderson Power Poles.
This allowed me to use several LiPo packs
I had on the shelf and one of my high-end
balancing chargers.
The AR.Drone comes with its own
balancing charger, but I’ve found by
comparing the state of charge and balance
to the ones from my other chargers, it’s not
the best. Then again, I’m comparing this to
chargers that cost almost as much as this
entire system, so take that for what it’s
worth. The system it comes with will serve
you well.
Taking Off: It’s off to the shop. I still have
many projects in the works and warmer
weather will be here before you know it. I
hope I’ll be showing you a great conversion
of an old aerotow tug that’s been in storage
for 15 years and is now being reborn as an
electric. It should be awesome! MA