Electrics - 2008/02

IN THE LAST column we looked at MotoCalc (Mcalc), which is
one of the two electric-flight simulation programs I feel are the
best. This month we will continue that discussion by looking at
ElectriCalc.
These “tools” might not fit your notion of tools, but we can use
them to optimize our projected setups before we lay out the money
for the gear. They are a must-have for electric-power fliers.
ElectriCalc is the brainchild of Dr. Sid Kauffman: electrical guru
and owner of SLK Electronics, which offers design consulting to a
wide variety of industries. Sid is located near the Research Triangle
Park in North Carolina and, more importantly to me, close enough
to go flying with occasionally.
I have known Sid and flown with him for roughly 15 years. His
experience in the electronic field, along with his teaching
experience, makes him one of the most helpful people around. He
designed ElectriCalc to help the modeler design a system and to
avoid wasting money by using a shotgun approach to equipment
selection.
The teacher in Sid comes out in the incredible tutorial that is
included in the help section of the program. I recommend that you
go through the entire tutorial before you do anything else with the
program.
It is set up to run as a timed slide presentation with explanations
or you can scroll through the screens at your own pace by doing it
manually. Your time will be well spent and it will teach you things
you might have thought you understood and did not.
Opening Screen: One of the things I like best about ElectriCalc
(Ecalc) is that everything is on the first screen that appears. It’s
divided into four sections: power, motor, drive, and flight
parameters.
I’ll go through each section briefly, but the beauty of this screen
being set up this way is that you can change one element of a
parameter and see all the changes it causes across the board. The
sliders are live, so you can change throttle setting or speed setting
and see how that affects everything else. This simple setup makes
ElectriCalc helps take the guesswork out of power-system choice
February 2008 119
Electrics Greg Gimlick | [email protected]
ElectriCalc has
an extensive
help section and
an automated
tutorial. This
itself is worth
the cost of the
program.
The motor database shows the parameters of the Neu the author
chose for the LT-25. Each motor can be edited as desired and saved.
This window lets you determine the drag coefficient the
program will use to determine overall performance. It’s simple
and requires no engineering degree!
ElectriCalc’s opening screen, where you’ll spend your time
working. Everything can be done from here.
9021
pm
m
hts!
02sig4.QXD 12/20/07 11:07 AM Page 119The help section has this screen for
determining CG locations if you’re doing
your own design. It is valuable to anyone
who is interested in design but not an
expert. The explanation comes up
alongside the parameters you need to
enter.
120 MODEL AVIATION
this program the choice of many beginners.
Look at the Flight Parameters section
and notice the “Plane Wt. ounces” tab. The
difference between Ecalc and Mcalc is that
Ecalc uses a total weight including motor,
controller, radio, and batteries, whereas
Mcalc uses a weight figure of only the
airframe and radio.
That isn’t a big deal to me, but it’s
something to be aware of. As you change
cell count or type in Ecalc, the program will
automatically adjust the weight to reflect
the change.
Help: Assistance is available anytime and
anywhere you’re working in the screen.
You can go to the Help section and search
for your question in the index or use a
clever little device Sid devised.
On the menu bar at the far right is a
Airplane Kadet LT-25 Kadet LT-25 Kadet LT-25 Kadet LT-25 Kadet LT-25
Setup [Sig] [Sig] [Sig] [Sig] [Sig]
Prop KRPM 6.72 6.64 6.41 6.23 5.75
Motor KRPM 16.80 16.60 16.02 15.58 17.24
Prop Watts 499 536 635 703 418
Motor Watts 556 596 700 775 470
Motor Amps 33.5 36.3 44.1 50.1 27.6
Motor Volts 16.6 16.4 15.9 15.5 17.0
Battery Amps 33.5 36.3 44.1 50.1 27.6
mAh 2300 2300 2300 2300 2300
Minutes 3.9 3.6 3.0 2.6 4.8
% Throttle 100 100 100 100 100
% System Eff. 79 78 76 74 80
% Motor Eff. 94 95 95 96 94
*Prop Diameter 14.00 14.00 15.00 15.00 14.00
*Prop Pitch 9.00 10.00 10.00 12.00 12.00
Pitch mph 56 62 59 70 64
Plane oz. 105 105 105 105 105
Wing sq. in. 724 724 724 724 724
Wing oz./sq. ft. 20.9 20.9 20.9 20.9 20.9
Drag coeff. 0.077 0.077 0.077 0.077 0.077
Watts/pound 85 91 107 118 72
Climb ft./min. 1221 1269 1533 1585 978
Climb angle 55 58 90 90 41
Max ft./min. 1677 1802 2226 2427 1342
@ angle 37 37 46 48 28
Max climb ft. 6564 6506 6617 6351 6372
Cruise Minutes 10.4 9.9 9.5 8.3 11.3
Stall mph 17 17 17 17 17
Max. mph 58 60 62 66 56
Speed mph 17 17 17 17 17
Thrust oz. 95 99 117 121 78
Drag oz. 10 10 10 10 10
Motor Neu 2215 Neu 2215 Neu 2215 Neu 2215 Neu 2215
Type /1.5Y BAM /1.5Y BAM /1.5Y BAM /1.5Y BAM /1.5Y BAM
Manufacturer NeuMotors NeuMotors NeuMotors NeuMotors NeuMotors
Kv 1020 1020 1020 1020 1020
Rm 4 4 4 4 4
Io 1.60 1.60 1.60 1.60 1.60
Km 21.00 21.00 21.00 21.00 21.00
*Gearing 2.50 2.50 2.50 2.50 3.00
% Gear Eff. 95 95 95 95 95
Motor Config. 1 1 1 1 1
Prop APC-E APC-E APC-E APC-E APC-E
Type
K Prop 1.21 1.21 1.21 1.21 1.21
K Pitch 0.20 0.20 0.20 0.20 0.20
K Eff. 1.05 1.05 1.05 1.05 1.05
Cell Type A123-M1 A123-M1 A123-M1 A123-M1 A123-M1
Cell Count 6 6 6 6 6
Pack Weight Oz. 15.0 15.0 15.0 15.0 15.0
Cell Volts 3.15 3.15 3.15 3.15 3.15
Cell mohm 8.9 8.9 8.9 8.9 8.9
ESC mohm 15 15 15 15 15
Altitude ft. 0 0 0 0 0
Temperature F. 77 77 77 77 77
02sig4.QXD 12/20/07 11:11 AM Page 120question mark. If you click on that, you’ll
have a cursor arrow with a bold question
mark next to it. Take that to whatever
parameter you have a question about and
click on it. You’ll be presented with a small
window defining the parameter you clicked.
There’s no searching or digging for
information—just a quick and easy block of
information.
Databases: There are extensive databases
for each section pertaining to motors,
batteries, and propellers. Each is accessible
from a button in the parameter group and is
fully capable of being edited by the user.
This is important because the
manufacturer’s motor constants or battery
parameters don’t always match real-life
findings. They are usually close enough that
there won’t be a huge difference in your
results, but editing does allow you to finetune
the program or add new components to
it as they are developed.
One of the ElectriCalc Web site’s
features is database updates. Be sure to back
up your old files prior to doing that.
Battery Parameters: This is the section on
the left. It will allow you to choose what
type of battery and how many cells you will
use.
The database is extensive and will
probably have the cells you’re looking for.
If you can’t find them, you can do an online
search of the various forums, and chances
are you’ll come up with the numbers you
need.
Most people find that if the voltage and
current predictions differ greatly from the
projection, they can adjust the voltage in the
respective tab and bring the program in line
with real-time data-acquisition info. Others
change the cell resistance in milliohms, but I
find it easier to just change the cell voltage.
Your mileage may vary.
Motor Parameters: The next section
contains all the data for the motors in the
database. You can edit the database and add
motors as you want.
With the constant influx of new motors
on the market, it’s nearly impossible to keep
this section up to date. Fortunately the
online forums are a wealth of information
about motor parameters, and you can find
almost anything you need to add without
doing your own testing.
Since this section is made up of the three
primary motor constants we refer to in
electrics, I’ll touch on some of that now.
Recently I’ve had some errors printed
because of editors misunderstanding the
abbreviations we use. Since that happens I
assume it can also happen with readers who
are unfamiliar with our technical terms, so
I’ll pull the definitions from Ecalc’s help
files.
Kv is a motor constant, expressed in
rpm/volt, that indicates how fast the motor
would turn for a given voltage if there were
no internal resistance. It is inversely
proportional to Kt: the torque constant.
Kv is usually measured by chucking the
motor shaft in a drill press (hold the motor!)
with a digital voltmeter (DVM) connected
to the motor leads. Run the drill press and
measure the DC volts from the motor
(generator). Divide the drill press rpm by
the measured voltage. This should be done
with neutral timing.
Io is a motor constant (Izero), expressed
in amps, that indicates the amount of current
necessary to turn a motor without load, or
how much current does not contribute to the
output power. Io is easy to measure, but it
generally requires the motor to be at neutral
timing. In fact, we say we have neutral
timing when we adjust for minimum Io.
This must be done quickly since a motor
gets surprisingly hot under these conditions.
Rm is a motor constant, expressed in
milliohms, that characterizes the equivalent
internal resistance of the motor. Rm is the
most difficult motor constant to measure.
You typically need to supply approximately
10 amps to the motor while keeping the
motor shaft from turning while measuring
motor voltage and current. You need an
accurate DVM to measure the voltage, and
an Astro meter is fine for the current.
Drive Parameters: This section is
information about the propeller and gearing
you’ll use. The constants for the main
brands of propellers we run into are in the
database, and figuring them on your own is
122 MODEL AVIATION
next to impossible. The manufacturers
provide these, and they should be taken as
provided.
The other parameter is the gearing you
intend to use. If you’re using direct drive,
plug in “1” for the ratio. Being able to
change the gear ratio is a big help when
looking at your overall decision on power
setups because it allows you to see all the
changes in current and performance as soon
as you enter the new ratio.
You can change the ratio and save the
motor along with that ratio in your motor
database so you won’t have to re-enter it the
next time. This program is incredibly
flexible.
Flight Parameters: The section on the right
describes the wing area, ready-to-fly weight,
wing loading, drag coefficient, and motor
configuration. The first three are selfexplanatory,
and the fourth usually makes
people’s eyes roll back in their head.
Don’t panic. As does Mcalc, this
program makes it easy for you to
guesstimate this difficult parameter without
having to get your aeronautical engineering
degree. If you know the airfoil shape, the
model’s general characteristics, and how the
landing gear is configured, it will come up
with a number for you.
The motor configuration is how many
motors you’re using and how they are
wired. This lets you estimate performance
for multiengine models and will help you
decide where you want to wire them in
parallel or series. If you’re confused by that,
you’ll be happy to know that diagrams are
provided in the help files to explain it.
The Results: Everything about the setup’s
performance is shown below each section.
As you change the throttle or airspeed
slider, you can watch the numbers change. If
you change anything within any of the
parameter columns, you’ll instantly see the
results in the areas below.
You can hit the print menu and get a
complete listing of the setup, and lay it
alongside other setups. This lets you
compare them side by side. This is a great
feature of both Ecalc and Mcalc.
I have included the printout for the LT-
25 I’ve been writing about. I made changes
in propeller size, highlighting the significant
elements of change.
Final Approach: I could go on and on
showing you both programs’ capabilities,
but it would fill a book. You won’t go
wrong with either, and you’ll be glad you
spent the little bit of money they cost. Check
out Ecalc’s Web site, and all the help files
are there to read through.
Now, enough of the computer work; go
out and fly! MA
Sources:
SLK Electronics
(336) 676-1681
www.slkelectronics.com/ecalc/index.htm
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