Electrics - 2009/08

TAKING OFF: This month I’ll update you
on my converted Multiplex Royal Evo 12
radio and then look at some terms we run
into when dealing with ESCs. That’s a lot for
one column, so let’s get going.
“Spektrumized” Evo, aka Franken-Evo: In
the June column I showed you my Evo radio
with a module fastened to the back with
Velcro, using Michel Moret’s ingenious way
of utilizing a stock Spektrum 2.4 GHz
module for Futaba radios. Jim Ryan of Ryan
Aircraft is to credit
for our latest
conversion effort
using the Spektrum
system, and it’s the
cleanest method I’ve
seen.
Remember that
doing this sort of
experimenting will
void any warranty.
Michel made a
version of his “light
adapter” without the
plug for us so we
could wire it directly
to the back of the
radio motherboard.
This allowed us to
install a plug inside
that connects the
adapter wire from the
Spektrum module,
Also included in this column:
• ESC intro
Update on the Franken-Evo
Electrics Greg Gimlick | [email protected]
The Power RC Electronics conversion of the author’s Royal Evo radio. The red plug
disconnects the module for removal and conversion back to his XPS system.
Jim Ryan soldered wires to the universal plug on the backside of
the motherboard that connects to Power RC Electronics’ “lite”
module. If you don’t solder excellently, don’t attempt this.
Jim Ryan fashioned a brass tube
and plastic bushing to get the
antenna to fit perfectly in the
channel.
which makes it removable, which allows me
to disconnect this system and return it to my
XPS system in minutes.
The challenge with this installation is the
antenna. We wanted to make it internal, as
with the one that the XPS uses, and we were
able to order some custom antenna
connections from an eBay dealer in China.
These wires are perfect and only required
us to drill a small hole on the module board,
to provide support and strain relief. We
drilled a hole in the back case, to gain access
to the binding button, and everything works
great.
If you’re the experimenting type and want
to try this, contact Michel at his Power RC
Electronics Web site. This is a much easier
way to convert the radio than any other
methods I’ve seen for hacking the Spektrum
modules. The photos tell the story.
ESCs 101: Read the instructions! This may
seem elementary, but it’s the number-one
reason behind most of the questions I get and
how people manage to damage equipment.
Yes, they are boring, but they are terribly
important. I can’t overemphasize that
enough.
The instructions not only tell you about
the programming options, but they also let
you know how to avoid damaging your
model or equipment. The instructions contain
safety tips that are important, so read them
programming. Safety first!
Never trust an armed controller.
Controllers are smarter and safer than ever,
but I always treat them as if they are about
to start. Whether they have arming switches
or not, I treat them the same way.
Never leave a motor battery plugged into
a controller, even if it has an arming switch.
There will be a slight current drain that will
eventually kill your battery, so remove the
battery each time you finish flying.
The Big Myth: Many fliers still believe that
they can use a smaller controller than is
actually required, because they don’t plan to
run the motor at full throttle all the time. If
the system draws 40 amps at full throttle
and they know that the model flies fine at
half throttle, they assume that a 25-amp
controller will work. Wrong!
At the most basic level, an ESC is
nothing more than a switch. The controller
is either full on or off all the time. The
secret is that you’d be amazed by how
quickly it turns on and off. It does so
thousands of times per second, and the time
it’s on or off varies by throttle position.
All the way off means that
no power is being sent to the
motor; all the way on means
that power is being sent to the motor. Any
throttle position between off and on means
that the ESC is switching on and off, to
achieve the power required for that
position.
Why do we care? Because if your
system draws 40 amps at full throttle, it
also draws it at half throttle, but it’s only
there for a microsecond at a time. It’s still
40 amps, so you can’t expect a controller
rated at 25 amps to handle the setup even
at half throttle.
Basic Settings: Controllers have a myriad
of features that can be changed to optimize
your system. Some you will use and others
you will disable. I’ll cover the most
common elements. In most cases, your
controller will come with factory defaults
that will be okay for 90% of user
applications.
• Brake Setting: Most controllers will let
you decide if you want a brake set or not. It
can be set to “on” if you want your propeller
to stop when you reduce your throttle to
idle/off. This is mostly used for folding
propellers, but some fliers like to stop their
models’ propellers for better glide with the
motor off, even if it’s not a folding type.
There are settings for soft brake, hard
brake, and no brake. The default for most
manufacturers is no brake or soft brake, but,
again, read the instructions. Some Jeti
controllers default to full brake. If you’re
flying a helicopter, make sure that the brake
is set to “off.”
• Low-Voltage Cutoff: This feature ensures
that you don’t damage your Li-Poly pack by
drawing the voltage too low during a flight.
The default on most controllers is “auto,”
and most of the time that is fine.
Various brands use different methods to
determine that, but the standard is
somewhere near 70%-75% of the voltage
level detected when first armed. This is
important, because if you fly more than one
flight on a pack without recharging between
flights, the controller may misinterpret the
voltage to drop too low.
A three-cell Li-Poly pack is fully charged
at 12.6 volts and the nominal voltage is 11.1.
The ESC accurately detects the cell count
and sets the cutoff at 75%, or 9 volts,
assuming that it sees 12 volts when you
connect it. You fly around and land with
plenty of power left.
After a break, you reconnect the same
pack without charging and it detects 11.5
volts. The ESC sets the cutoff at 75%, or
8.12 volts. That’s too low for a three-cell
pack, since you’ve discharged it to 2.8 volts
per cell and they don’t like much less than 3
volts per cell. This example isn’t too bad, but
you can see the potential problem with
multiple flights before recharging.
Check your ESC’s instructions. Some set
for 3 volts per cell, and you get a tone upon
arming that lets you know how many cells
the ESC thinks are in your pack. Be sure to
verify that it is correct before flying.
Some controllers allow you to override
the auto setting and select a minimum
discharge voltage. Always fly with a freshly
charged pack, so that the controller has the
best chance of properly identifying the cell
count.
• Cutoff Mode: Most controllers allow you to
choose whether you want a hard or soft
cutoff when it reaches its minimum voltage
level. A hard cutoff means that your motor is
going to stop when the voltage is reached.
A soft cutoff means that the motor will
pulse on and off, to let you know it’s time to
land. When this happens, you can often
reduce your throttle to idle for a second and
then return to normal operation long enough
to get the model on the ground.
Don’t abuse this ability. It is overriding
the cutoff and meant to give you power to
avoid a dead-stick landing.
• Startup Mode: This defines how the motor
starts when you open the throttle. The
choices are generally “normal,” “soft start,”
and “super soft start,” or something similar.
It will probably be self-explanatory.
Normal is usually the default and fine for
most airplanes. If you’re flying an aircraft
with a gearbox, you might want to select
soft, to make it easier on the gears and motor
when it starts.
If you are flying a helicopter, you will
want a very soft start most of the time, to
soften the strain on the main gear while the
motor attempts to get the rotor blades
started. Using normal on a helicopter often
strips a gear.
• Timing: This causes more questions than a
paragraph or two can answer. The default for
most ESCs is “standard” or “medium.”
Unless you really want to get into learning
motor theory and optimize for competition,
you’re safe leaving this alone.
The instructions will provide special
notes in case you have a problem with your
motor running roughly, and that’s the best
place to go. With a park flyer, chances are
that you won’t use a motor that requires
special timing. I will go into this in a later
column, but sticking with the default setting
is usually a safe bet. Some ESCs will instruct
you to set it for “high” on some outrunners.
• PWM Switching Frequency: Again, stick
with the factory defaults unless there is a
problem. If you encounter an issue, check
the instructions or contact technical support.
A full description of this is beyond the
scope of this introduction. This figure
represents the number of times per second
that a pulse is sent to the motor. This might
be between 8,000 and 32,000.
• Operating Mode: Some controllers give
you the option of selecting a preprogrammed
set of parameters such as “airplane,”
“glider,” or “helicopter.” When choosing one
of these operating modes, the ESC will have
preset features to optimize that choice.
When choosing “helicopter,” many
controllers will let you activate a governor
mode to help with throttle/collective
coordination and use the softest start mode.
The “glider” mode usually sets a hard brake,
assuming that you’re using a folding
propeller.
One Last Thing: I get many questions about
how to connect the three wires to the motors.
This is easy; it doesn’t matter.
Hook up the wires in any order. If the
motor runs backward, change any two wires.
You won’t hurt a thing. Some ESCs will also
let you reverse the motor’s direction in its
programming.
One More Last Thing: I talked to Tim
Dawson of Approach Engineering about his
all-balsa scale helicopter kits. He bought the
company after James Linder died last year
and has been tooling up for full production.
I’m happy to report that Tim is in full
gear now, and kits are available in all sizes
from Starwood Scale Models. His Dawson’s
Approach Engineering Web site is also in
full swing.
These are high-quality, laser-cut kits into
which you can drop several 30-size
helicopter mechanics. There is also a new
60-size Cobra out for those who like larger
scale models. I’ve built the eCobra and will
be constructing the Apache soon. Check
them out!
One more thing: Tim donates a portion of
all proceeds to a fund for James Linder’s
three sons. That’s class worth supporting.
Final Approach: We can do so much with
our ESCs because of their program options.
There are multiple ways to change the
settings, but I prefer the external devices-tothe-
transmitter method. It’s easier, and you
can see all the options without having to
count beeps and move the throttle stick. I’ll
show you some of these later. MA
Sources:
Michel Moret Power RC Electronics
[email protected]
www.power-rc-electronic.com
Ryan Aircraft
(513) 729-3323
http://home.fuse.net/ryan/
Starwood Scale Models
(650) 851-9027
www.starwoodmodels.com
Dawson’s Approach Engineering
220 W. Mariposa Ave.
Ridgecrest CA 93555
www.approachengineering.com