Electrics - 2008/02 | Model Aviation Library

Author: Greg Gimlick

Edition: Model Aviation - 2008/02
Page Numbers: 119,120,122

ElectriCalc helps take the guesswork out of power-system choice

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 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 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 on 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 question-mark icon. 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 fine-tune the program or add new components to it as they are developed.

One of the ElectriCalc website'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: 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: 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: 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 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 self-explanatory, 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.

Airplane Setup

Airplane: Kadet LT-25 (Sig) — five configurations

Configuration 1

Prop KRPM: 6.72
Motor KRPM: 16.80
Prop Watts: 499
Motor Watts: 556
Motor Amps: 33.5
Motor Volts: 16.6
Battery Amps: 33.5
mAh: 2300
Minutes: 3.9
% Throttle: 100
% System Eff.: 79
% Motor Eff.: 94
Prop Diameter: 14.00
Prop Pitch: 9.00
Pitch mph: 56
Plane oz.: 105
Wing sq. in.: 724
Wing oz./sq. ft.: 20.9
Drag coeff.: 0.077
Watts/pound: 85
Climb ft./min.: 1221
Climb angle: 55
Max ft./min.: 1677
@ angle: 37
Max climb ft.: 6564
Cruise Minutes: 10.4
Stall mph: 17
Max mph: 58
Speed mph: 17
Thrust oz.: 95
Drag oz.: 10
Motor: Neu 2215
Type: /1.5Y BAM
Manufacturer: NeuMotors
Kv: 1020
Rm (mΩ): 4
Io (A): 1.60
Km: 21.00
Gearing: 2.50
% Gear Eff.: 95
Motor Config.: 1
Prop: APC-E
K Prop: 1.21
K Pitch: 0.20
K Eff.: 1.05
Cell Type: A123-M1
Cell Count: 6
Pack Weight Oz.: 15.0
Cell Volts: 3.15
Cell mohm: 8.9
ESC mohm: 15
Altitude ft.: 0
Temperature F.: 77

Configuration 2

Prop KRPM: 6.64
Motor KRPM: 16.60
Prop Watts: 536
Motor Watts: 596
Motor Amps: 36.3
Motor Volts: 16.4
Battery Amps: 36.3
mAh: 2300
Minutes: 3.6
% Throttle: 100
% System Eff.: 78
% Motor Eff.: 95
Prop Diameter: 14.00
Prop Pitch: 10.00
Pitch mph: 62
Plane oz.: 105
Wing sq. in.: 724
Wing oz./sq. ft.: 20.9
Drag coeff.: 0.077
Watts/pound: 91
Climb ft./min.: 1269
Climb angle: 58
Max ft./min.: 1802
@ angle: 37
Max climb ft.: 6506
Cruise Minutes: 9.9
Stall mph: 17
Max mph: 60
Speed mph: 17
Thrust oz.: 99
Drag oz.: 10
Motor: Neu 2215
Type: /1.5Y BAM
Manufacturer: NeuMotors
Kv: 1020
Rm (mΩ): 4
Io (A): 1.60
Km: 21.00
Gearing: 2.50
% Gear Eff.: 95
Motor Config.: 1
Prop: APC-E
K Prop: 1.21
K Pitch: 0.20
K Eff.: 1.05
Cell Type: A123-M1
Cell Count: 6
Pack Weight Oz.: 15.0
Cell Volts: 3.15
Cell mohm: 8.9
ESC mohm: 15
Altitude ft.: 0
Temperature F.: 77

Configuration 3

Prop KRPM: 6.41
Motor KRPM: 16.02
Prop Watts: 635
Motor Watts: 700
Motor Amps: 44.1
Motor Volts: 15.9
Battery Amps: 44.1
mAh: 2300
Minutes: 3.0
% Throttle: 100
% System Eff.: 76
% Motor Eff.: 95
Prop Diameter: 15.00
Prop Pitch: 10.00
Pitch mph: 59
Plane oz.: 105
Wing sq. in.: 724
Wing oz./sq. ft.: 20.9
Drag coeff.: 0.077
Watts/pound: 107
Climb ft./min.: 1533
Climb angle: 90
Max ft./min.: 2226
@ angle: 46
Max climb ft.: 6617
Cruise Minutes: 9.5
Stall mph: 17
Max mph: 62
Speed mph: 17
Thrust oz.: 117
Drag oz.: 10
Motor: Neu 2215
Type: /1.5Y BAM
Manufacturer: NeuMotors
Kv: 1020
Rm (mΩ): 4
Io (A): 1.60
Km: 21.00
Gearing: 2.50
% Gear Eff.: 95
Motor Config.: 1
Prop: APC-E
K Prop: 1.21
K Pitch: 0.20
K Eff.: 1.05
Cell Type: A123-M1
Cell Count: 6
Pack Weight Oz.: 15.0
Cell Volts: 3.15
Cell mohm: 8.9
ESC mohm: 15
Altitude ft.: 0
Temperature F.: 77

Configuration 4

Prop KRPM: 6.23
Motor KRPM: 15.58
Prop Watts: 703
Motor Watts: 775
Motor Amps: 50.1
Motor Volts: 15.5
Battery Amps: 50.1
mAh: 2300
Minutes: 2.6
% Throttle: 100
% System Eff.: 74
% Motor Eff.: 96
Prop Diameter: 15.00
Prop Pitch: 12.00
Pitch mph: 70
Plane oz.: 105
Wing sq. in.: 724
Wing oz./sq. ft.: 20.9
Drag coeff.: 0.077
Watts/pound: 118
Climb ft./min.: 1585
Climb angle: 90
Max ft./min.: 2427
@ angle: 48
Max climb ft.: 6351
Cruise Minutes: 8.3
Stall mph: 17
Max mph: 66
Speed mph: 17
Thrust oz.: 121
Drag oz.: 10
Motor: Neu 2215
Type: /1.5Y BAM
Manufacturer: NeuMotors
Kv: 1020
Rm (mΩ): 4
Io (A): 1.60
Km: 21.00
Gearing: 2.50
% Gear Eff.: 95
Motor Config.: 1
Prop: APC-E
K Prop: 1.21
K Pitch: 0.20
K Eff.: 1.05
Cell Type: A123-M1
Cell Count: 6
Pack Weight Oz.: 15.0
Cell Volts: 3.15
Cell mohm: 8.9
ESC mohm: 15
Altitude ft.: 0
Temperature F.: 77

Configuration 5

Prop KRPM: 5.75
Motor KRPM: 17.24
Prop Watts: 418
Motor Watts: 470
Motor Amps: 27.6
Motor Volts: 17.0
Battery Amps: 27.6
mAh: 2300
Minutes: 4.8
% Throttle: 100
% System Eff.: 80
% Motor Eff.: 94
Prop Diameter: 14.00
Prop Pitch: 12.00
Pitch mph: 64
Plane oz.: 105
Wing sq. in.: 724
Wing oz./sq. ft.: 20.9
Drag coeff.: 0.077
Watts/pound: 72
Climb ft./min.: 978
Climb angle: 41
Max ft./min.: 1342
@ angle: 28
Max climb ft.: 6372
Cruise Minutes: 11.3
Stall mph: 17
Max mph: 56
Speed mph: 17
Thrust oz.: 78
Drag oz.: 10
Motor: Neu 2215
Type: /1.5Y BAM
Manufacturer: NeuMotors
Kv: 1020
Rm (mΩ): 4
Io (A): 1.60
Km: 21.00
Gearing: 3.00
% Gear Eff.: 95
Motor Config.: 1
Prop: APC-E
K Prop: 1.21
K Pitch: 0.20
K Eff.: 1.05
Cell Type: A123-M1
Cell Count: 6
Pack Weight Oz.: 15.0
Cell Volts: 3.15
Cell mohm: 8.9
ESC mohm: 15
Altitude ft.: 0
Temperature F.: 77

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 website, and all the help files are there to read through.

Now, enough of the computer work; go out and fly! GG

Sources:

SLK Electronics
Phone: (336) 676-1681
www.slkelectronics.com/ecalc/index.htm

Transcribed from original scans by AI. Minor OCR errors may remain.