Copyright: Copyright 1998, SLK Electronics, L.L.C.
Citation: All rights reserved.


Table of Contents
Contents

Introduction

Overview

Power Parameters

Motor Parameters

Drive Parameters

Flight Parameters

Basic Operation

Using Databases

Cells Database

Motors Database

Props Database

Planes Database

Printing & Saving Results

Estimating Coefficient of Drag

Multiple Motor Configurations

Working with Graphs

Prop Selection Graphs

System Efficiency Graphs

Thrust & Drag Graphs

Data Analyzer

Sorting Data

Shortcut Keys

Odds & Ends

Typical Resistances

References

Shoo-fly Pie


  Introduction

Electric flight is exciting and challenging. The choices are much more complex than with liquid-fueled power plants. Electric motors are far more versatile, but with this comes a confusing array of choices of propellers, gearboxes, batteries, etc. The energy-to-weight ratio of batteries is far less than that of liquid fuels. Careful selection of each component of the power system is vital.

ElectriCalc is the most powerful tool available for electric flight. It allows you to quickly evaluate your options and provides you assurance of success. ElectriCalc's main screen provides all the information you need to evaluate the performance of your system. As you change parameters, all data is automatically updated before your eyes. You can perform "What if?" scenarios to your heart's content. You will quickly learn how components interact. ElectriCalc's other screens provide powerful tools for working with the databases , printing , using graphs as design tools, and analyzing and evaluating large amounts of data.

All databases are in ASCII format that can be edited with any text editor, and new data can be easily entered, deleted, and edited both in the program and externally.  It is hoped that the open architecture of the databases will encourage sharing of data.  You can get the latest databases, contribute data, or ask questions at the ElectriCalc web site .

If you're one of those guys who never reads the directions and just pushes buttons, go ahead. However, we would strongly recommend reading either the manual or the help program (by using the "browse" buttons at the top of the screen), or using the tutorial.

Enjoy !

PLEASE READ THE FOLLOWING CAREFULLY :

This program is not intended to put a man on the moon or otherwise provide a near-perfect simulation of any system.  There are simply too many variables to account for.  Motor and battery parameters change with temperature and that temperature is a function of how well it is cooled in the plane as well as the motor construction.  Props often have a pitch significantly different from that advertised.  The list goes on, but hopefully you get the picture.  Also, the numbers in this program do not come with a guarantee.  As long as you keep things in perspective, this program will help you to make good choices on system components.  You'll be picking close to the right prop the first time.  However, please don't use this program to conclude that motor A is better than motor B based only on a small difference in performance numbers in this program.  This program will not tell you how much current/power a motor can handle or how durable the motor is.  The program does not care if the motor is turning too fast in your setup. Likewise with power dissipation. Read the manufacturers specs. Talk to others. Use common sense.


   Overview

The main ElectriCalc screen is divided into 4 panels. From left to right they are Power Parameters, Motor Parameters, Drive Parameters, and Flight Parameters. Intuitively, this is the flow of energy from the battery to the airplane.

The top section of each panel has text boxes where information can be entered. If you click your mouse pointer in a text box, you can edit the data in the box. If you double-click, the box will turn blue and the first key you press will delete the previous data. Pressing the Enter key or clicking on another object will cause all other data to be recalculated automatically. In addition to normal editing, you can use the + and - keys to step the number up or down in fixed steps, e.g. change the prop diameter in steps of 0.5 inches.  The Amps and Wing Load boxes, when changed, will cause other panels to "light up."  This allows some reverse calculations to be performed.

The Motor Configuration text box on the Flight Parameters panel looks different and it is. When you click on it you will get a screen that will allow you to set up multiple motor/prop configurations .

The bottom section of each panel contains calculated data that is not directly changeable by the user. This information might seem bewildering at first, but it is logically arranged. Every time you change a number, you can immediately see the effect it has on your system.

ElectriCalc has 4 databases for Cells, Motors[w/gearbox], Props, and Planes, (which we will often call "setups"). Each large button will display a screen that allows you to select and manipulate data. The buttons with arrows allow you to move back and forth through the data. Of course, all other data changes automatically. If you hold the right mouse button down when the cursor is over a database button, the associated text boxes will "light up". The Planes database includes the settings of the other 3 databases and holding down the right mouse button lights up all data.

The Power Parameters panel has an additional Throttle slider that simulates the operation of an Electronic Speed Control (ESC). The "slider" control has the same effect on the motor as your throttle stick controlling a high-rate speed control. This is a type of ESC where the switching rate is independent of the transmitter, typically 1-5 kHz. A frame-rate ESC is a type of ESC where the switching rate is the same as the rate that the transmitter sends out data, typically 20-30 ms.  This is very inefficient (gets hot) at partial throttle. You can use this slider to see what your system does "throttled back".

The Flight Parameters panel has an additional MPH slider that specifies the speed to be used in the aerodynamic calculations. This "slider" control sets the flying speed of the aircraft, which affects the aerodynamic calculations, such as thrust and drag.


   Power Parameters

This is simply the number of cells in your flight battery pack. Stored in Planes database. The most popular values are 7 and 10 cells. It is common to hook packs in series to make larger sizes. If you need to model two packs in parallel, create a new cell type with half the Cell mohm and twice the MAH and name it something like "2xRC2000".

This is the nominal internal cell voltage. Stored in file ECALC.INI . This is not the voltage you would measure under load, since this would also include the drop due to the internal resistance. A NiCad normally starts at 1.30-1.35 volts, levels off at around 1.25, and at 1.20 is about empty! The simple model of a NiCad cell is an ideal voltage source and a series resistance. During the 'plateau' of the discharge curve the voltage drops a few hundredths of a volt. We have measured 1.25 as a typical value but some feel that a slightly lower number is more realistic.

This is the equivalent cell resistance in milliohms. Stored in Cells database. The lowest resistance is obtained with end-end soldered cells. Cell resistance should include the resistance of the cell interconnections.  The original data assumes minimal (end-end soldered) resistance. Bars or heavy braid will be somewhat more (+0.5 milliohm) and welded tabs could be substantially more (>1 milliohm). You can measure this yourself with a good DVM, ammeter, and load. Basically you need to measure under load and no-load voltage quickly so that chemical processes do not interfere. Use at least a 10-amp load. Cell resistance is voltage difference divided by load current divided by number of cells. See our web site for information on end-end packs.

This is the equivalent resistance of the ESC (Electronic Speed Control) plus all the wiring and the connectors, fuse(s), and switch(es). Stored in Planes database . The resistance of ESCs is a function of design and number and type of FETs. Also, brushless controllers have inherently higher resistance because they must switch both sides of the winding and this requires p-channel FETs with higher resistance. High performance brushless controllers have a bunch of FETs.

This is the typical milliampere-hour capacity of a cell. Stored in Cells database . This basically means that the cell can supply that many milliamps for one hour before the voltage drops substantially. This is generally higher than the manufacturer's rating, but will vary as a function of the charge method, discharge rate, and temperature. This number is used to estimate the motor run time at the calculated battery current. MAH is normally measured assuming a cutoff voltage of one volt or less. With high cell-count packs you can't afford to let the pack get down this low per cell without risking damage to the lower-capacity cells. You can expect the capacity of a higher cell-count pack to appear less due to the higher probability of a spread in cell capacities.

This is a description of the selected cell. Stored in the Cells database . These cells are mainly Sanyo. The most popular are the N-1700SCRC and RC2000 for sport flying, and the KR-600AE and N-500AR for the smaller "Speed 400" models. This brand has a proven track record. Cells with an 'R' in the suffix are especially suited for the high charge and discharge rates needed for electric flight. Other cells have a higher energy to weight ratio but at the expense of lower current handling and/or charge rate.

 This is the Cells database control. If you click the big button, you jump to the Cells database. The smaller buttons step you back and forth through the database. Use CTRL_C as a shortcut to access the database. This selects the cell information on the screen which includes cell resistance, cell capacity in MAH, and a description of the cell.

This is the current supplied by the battery. It is equal to the motor current at full throttle and less than the motor current at partial throttle. For motors wired in parallel, the battery current is the total to all motors. At part throttle, battery amps will be less than motor amps. This seems wrong, but what is happening is sort of a transformer effect. The watts out of the battery are roughly the same as the watts into the motor. However, the ESC essentially lowers the average motor voltage. If you have the same wattage, you must have more current. How can this be? When the ESC switches off the motor. The current in the motor continues to flow via a special diode or equivalent in the ESC.

This is the estimated battery duration at the indicated current. This number is often much lower than the flight time you would like. The key to success is intelligent use of the throttle.

This is the percentage of total energy that is delivered to the propeller. This does not include any propeller losses, but includes losses in the cells, wiring, ESC, and the motor itself. Generally, efficiencies below 45% for ferrite motors and 50% for others indicates an overloaded system. Use the System Efficiency graph to figure out where the problem is.

This is the power supplied by the ideal battery, not including losses due to internal cell resistance. This is the denominator in determining system efficiency. In the ideal cell model, this is the cell open-circuit voltage times the current times the number of cells.

This is the power loss in the battery, wiring, and ESC. Most of the loss will be in the pack itself, so the lower the cell resistance the better. It's not a bad idea to check your wiring with a DVM with the motor running to look for excessive voltage drops. At 20A, you should generally see less than 0.02V across connectors & switches.

 This is an estimate of the pack weight based on the weight per cell from the Cells database plus a small amount for solder and shrink wrap. End-end soldering yields the lightest packs. Braid works well but a lot of solder can wick into the braid. You can save a little weight by removing the wrapper(s) but you must be REALLY careful how you handle the cells and how you insulate the pack.

This is the current at which the % system efficiency will be maximized. This always occurs at a lower current than the maximum motor efficiency current. For sport flying you don't want your full-throttle current to be this low. It's better to prop for something higher than max. sys. eff. current, and use your throttle.

This is the duty cycle of the (high rate) ESC. This is controlled by a slider control. This reduces the average voltage seen by the motor(s). Clicking the arrows steps 1% and clicking in the white area steps 5%. Set your speed for twice stall speed and then back off the throttle until you get a 5-degree climbout. This is a good upper bound on your expected flight time.


   Motor Parameters

This 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. Stored in Motors database. It is inversely proportional to Kt, the torque constant. Kv is usually measured by chucking the motor shaft in a drillpress (hold the motor!) with a DVM connected to the motor leads. Run the drillpress and measure the DC volts from the motor (generator). Divide the drillpress RPM by the measured voltage. This should be done with neutral timing.

This is a motor constant , expressed in milliohms, which characterizes the equivalent internal resistance of the motor. Stored in Motors database . Rm is the most difficult motor constant to measure. You typically need to supply about 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. A battery pack with a load (power resistor or headlight) could supply the current. The motor timing does not matter, but shaft position can vary the reading. We like to take several readings while slowly rotating the shaft.

This 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. Stored in Motors database . 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.

This Is the computed motor current. You can also enter a desired current and the program will determine the prop diameter or pitch or motor gearing to obtain this current. This value is not stored in any database. If you enter a desired Amps value, the Diameter, Pitch, and Gearing text boxes will "light up". If you double-click on one of these, the program will recalculate its value to that which gives the Amps value entered.

This is the manufacturer or reseller of the motor. Stored in Motors database .

This is a description of the selected motor. Stored in the Motors database . Many of the European motors and the Aveox motors have a numbering system that describes the length and diameter of the motor. Unfortunately this standard is far from universal.

This is the Motors database control. If you click the big button, you jump to the Motors database. The smaller buttons step you back and forth through the database. Use CTRL_M as a shortcut to access the database. This selects a motor/gearbox combination, including Kv, Rm, Io, gear ratio, manufacturer and description.

This is the rotational speed of the motor in thousands (K) of revolutions per minute. If there is a gearbox, it is input side RPM. The motor tries to get the RPM to the value determined by Kv and the input voltage. The power required to turn the prop is proportional to the cube of the RPM. This load causes current to be drawn which reduces the voltage seen by the "ideal" motor. This ultimately results in an equilibrium where the motor is "happy".

This is the percentage of energy to the motor that is delivered to the propeller or gearbox. This does not include any propeller or gearbox losses, but includes losses in the motor itself. Motor efficiency is generally higher for rare-earth (cobalt and neodymium) magnets than for ferrite. However, high efficiencies can be attained with ferrite motors that are designed to run at very high RPM. These require a high-ratio gearbox and brush life is an issue. Brushless motors have somewhat higher efficiencies than brushed motors.

This is the power loss in the internal motor resistance and Io. This is what makes the motor get hot. This number is difficult to measure without a dynamometer.

This is the power supplied to the motor. It is the motor voltage multiplied by the motor current. This is the denominator in determining motor efficiency. This is easy to check with an Astro meter or equivalent. It is a good idea to do this with a new setup and compare it with ElectriCalc predictions. This frequently points out wiring and other problems such as a weak battery pack.

This is the voltage across the motor terminals. The RPM of an ideal motor model should be Kv times the difference of the motor voltage and the motor current times the internal resistance.

This is a number based on certain motor parameters that is an indicator of the "quality" of a motor. If you have two motors of about the same size, the one with the higher motor constant would generally be better. Larger motors generally have higher motor constants. Don't worry about this number. This number is obtained by taking the motor Kt and multiplying by the square root of Rm. The torque constant Kt is 1352 divided by Kv.

This is the motor input current that results in the greatest motor efficiency. It is higher than the current for best system efficiency. The motor efficiency curve is zero at Io and peaks rather quickly. It falls off gradually and is zero at Istall. It is generally better to prop higher than the max. eff. current as long as you keep within the rating of the motor.


   Drive Parameters

This is the propeller diameter expressed in inches. Stored in Planes database. The power required to turn a prop goes up as the 4th power of the diameter. There are pros and cons to 3-bladed props. They look cool (when the motor's not running) and save a little ground clearance. However, they're significantly less efficient and that's a BIG con.

This is the propeller pitch expressed in inches. Stored in Planes database . The number represents the number of inches the prop would advance if it were a screw in an inelastic medium. Pitch is normally measured at 75% of the distance from the center to the tip. The best pitch for most electric applications is between half the diameter (P/D=0.5) and the diameter (P/D=1.0). This assumption is used in some of the tools. TIP: try modeling a 6-10 pitch as an 8.5 or 9.0.

This is a propeller constant used in calculating the power absorbed by a propeller. Stored in Props database. It indicates the manufacturers generic prop shape and its effect on power. A prop with a higher Kprop absorbs more power for a given diameter and pitch. This number is difficult to measure, and much of the data is empirical. However, there is substantial variation in prop factors (usually pitch) in what you buy which often overshadows the accuracy of other numbers.

This coefficient accounts for efficiency differences between props, e.g. 2- vs. 3-blade. Stored in Props database . This coefficient is new to Version 2. The coefficient Kpitch from Version 1 is still used but can only be changed on the database screen .

This is the number of revolutions the motor must make to rotate the prop one revolution. Stored in Motors database. There is a gearbox efficiency number in the ecalc.ini file. You can change this by editing this file. ElectriCalc will not let you put unreasonable numbers here.

This is simply a brief description of the prop and manufacturer. Stored in the Props database .

This is the Props database control. If you click the big button, you jump to the Props database. The smaller buttons step you back and forth through the database. Use CTRL_P as a shortcut to access the database. This selects different prop types. This includes Kprop, Keff, Kpitch, and a description of the prop.

This is the rotational speed of the prop in thousands (K) of revolutions per minute. Dividing the motor RPM by the Prop RPM yields the gear ratio. When using a gearbox, you need to be aware that the motor is turning faster than the prop. There is a limit to how fast a motor should be allowed to turn. These limits are due to such factors as type of bearings, brushes, how the windings and magnets are secured, etc. These limits range from about 20K to 50K+. Check your motor data sheet.

This is the power supplied to the prop. It is an empirical equation which generally provides a reasonable approximation. This is the power into the prop from the motor/gearbox. How much of this actually moves the plane through the air is a function of the efficiency of the prop. This is a complex function. Best to experiment or share the experiences of others.

This is the ratio of the power into the motor(s) to the total weight of the plane. This is a rule of thumb measure of a planes flying ability. In general, 50 watts/lb. is indicative of a plane with adequate power, with higher numbers implying greater aerobatics capability. This is based on brushed cobalt motors. Ferrite motors generally require somewhat higher numbers for the same flight performance. Although this is a handy rule-of-thumb, ElectriCalc provides more important data such as climb rate and cruise time. Watts per pound doesn't guarantee your plane will climb.

This is the power loss in the gearbox. The benefits of using larger, slower-turning props generally outweigh these small losses. The gearbox efficiency factor is found in ecalc.ini and can be changed using a text editor.

This is the theoretical speed of a plane with zero drag, based solely on the pitch and RPM of the prop. Planes with low drag can fly faster than this number because of the 'lift' generated by the prop blades and the 'unloading' of the prop at higher speeds.

This is the force in ounces or grams provided by the motor(s) to pull or push the plane through the air. The difference between thrust and drag is what can provide acceleration and climb. There is controversy about the value of static thrust measurements as a figure of merit. If you study a typical thrust graph , you will see why these measurements can mislead. Lower-pitched props yield the highest static thrust, but this drops off more rapidly than a higher-pitched prop.

This is the force in ounces or grams due to the drag of the plane. This includes drag due to creating lift as well as drag due to the shape of the plane. At higher speeds, this second component is dominant, and is proportional to the square of aircraft speed.


   Flight Parameters

This is the total aircraft weight in ounces or grams. Stored in Planes database. Don't forget to adjust the weight if you change motors. This weight should be appropriate for the number and type of cells you have entered, since the program adjusts the weight with cell changes. ElectriCalc is not ambitious enough to keep up with the weight of hundreds of motor/gearbox combinations (or the weight of different props for that matter!).

This is the wing loading, or ratio of plane weight to total wing area expressed in ounces per square foot or grams per square decimeter. This value is calculated and not stored in any database. If you enter a value for wing loading, the Plane Wt. and Wing Area will "light up". Double-clicking on either of these will recalculate that value to correspond to the specified loading. This is useful for things like determining a target weight for a model when you know the wing area and the desired wing loading Tolerable wing loading goes up as the size of the plane increases. 18 oz. per sq. ft. is good for "Speed 400" size planes. 24 oz. per sq. ft. is good for "40-size" planes. 30+ oz. per sq. ft. can be tolerated in the very large models. Biplanes require lower loading because the two wings in close proximity are not as efficient.

This is the total wing area in square inches or square decimeters. Stored in Planes database. Wing area is normally considered to include the area over/under the fuselage. The area of a wing with non-parallel leading & trailing edges can be figured by taking the width at the center plus the width at the tip and multiplying by the length (perpendicular to fuselage) from the center to the tip.

This is an aerodynamic constant used in calculating the thrust required to move the plane through the air at a given speed. Stored in Planes database This number can be entered here or a reasonably good estimate can be quickly made by selecting C drag from the menubar.. Wing struts and wires add a lot of drag. A good aerodynamics text is "Model Airplane Design and Performance for the Modeler" by Howard Chevalier. Reduction of drag in electric models is quite important. Biplanes in particular give disappointing flight times. Thick airfoils, fat fuselages, struts and wires should be avoided or minimized wherever possible. Remember that wing loading also contributes to drag.

This is an alphanumeric representation of the motor configuration. Stored in Planes database. Information cannot be entered directly here, but can be selected by clicking the raised panel or the Multi menubar selection. Two motors in parallel have the same Kv , half the Rm , and twice the Io . Two in series have half the Kv, twice the Rm, and the same Io. Etc, etc.

This is a description of the selected plane. Stored in Planes database.

This is the Planes database control. If you click the big button, you jump to the Planes database. The smaller buttons step you back and forth through the database. Use CTRL_S as a shortcut to access the database. This selects the plane that is displayed. This includes the cell count, wiring resistance, prop diameter & pitch, weight, wing area, Cdrag, and motor configuration. It also selects a cell, motor/gearbox, and prop from their respective databases.

This is the rate of climb at the maximum climb angle possible at the current throttle and speed slider settings. Climb rate drops off dramatically with speed because the drag increases as roughly the square of the speed, and the available thrust drops with increasing speed. The climb rate has a peak between stall and max speeds that is related to the lift, drag, and thrust relationships.

This is the maximum sustainable climb angle at the current throttle and speed slider settings. It corresponds to the climb rate above. Physically, this number is derived from the amount of thrust remaining to lift the plane after subtracting that necessary to pull the plane through the air at the set speed. Climb angle (sustained) drops off dramatically with speed because the drag increases as roughly the square of the speed, and the available thrust also drops with increasing speed

This is the maximum rate of climb obtainable at the current throttle setting, independent of the speed slider. It is obtained at the angle indicated. The steepest climb angle does not yield the fastest climb.

This is the theoretical total height at the max climb rate for the indicated minutes. Although this number is calculated by multiplying the calculated max climb rate times the calculated minutes, it's really just a relative measure. It does not integrate this number over the discharge profile of the battery pack.

This is the theoretical minimum flying speed using a rule of thumb based on the wing loading. It is only an approximation but normally close enough. This number is the standard rule of thumb of 3.7 times the square root of the wing loading in oz. per sq. ft or grams per sq. dm.

This is the calculated maximum plane speed in level flight based on the thrust of the prop(s) and the drag of the plane. This is the speed where the thrust and drag curves cross. Climb rate is zero because there is no thrust available to lift the plane.

This is a magic number computed by ElectriCalc to give you a measure of flying time assuming mild maneuvers and good throttle management. This number is based on sustaining an average climb rate and speed related to the rate-of-climb vs. speed curve. This calculated speed is then obtained by backing off the throttle and then calculating the run time. It's just a guideline, not something to lose sleep over.

This speedometer control sets the speed at which you want the performance calculations made. More speed . . . less climb, more drag . . . less thrust, etc. Clicking the arrows steps 1% and clicking in the white area steps 5%. Try stepping the speed from stall to max and watching the rate of climb first increase and then decrease.


  Basic Operation

ElectriCalc is based on the ideal motor equations, which model a DC motor as a combination of ideal devices. This model consists of an ideal resistance in series with the parallel combination of an ideal current source and an ideal motor. The ideal motor attempts to turn its load at a speed that is directly proportional to its input voltage. The constant Kv is the ratio of RPM to voltage. This motor would draw a bizillion amps if the load were large enough, but the series resistance (or sometimes a fuse) limits this. The current source is the constant Io which describes the amount of current necessary to get the motor moving but which does not contribute to output power. The ideal resistance is Rm.

To model the load due to the propeller, an equation is used that relates propeller power to prop diameter, pitch, RPM, and constants that describe a manufacturer's particular style of props.

To power the motor model, the power source is characterized as an ideal voltage source in series with an ideal resistance. The voltage is the nominal cell voltage times the number of cells. The resistance is the internal cell resistance times the number of cells plus the wiring resistance plus the resistance of the speed control.

Hooking this up mathematically basically is done with a quadratic equation for current. The result is used to calculate the other motor-related parameters. Finally, the results can be tied in with an empirical thrust equation to calculate thrust. This is combined with some rudimentary aerodynamic parameters to estimate drag, climbing ability, stall speed and top speed.


  Using Databases

The databases in ElectriCalc were designed to allow easy updating and free interchange of data with other users. The four databases for cells , motors , props , and planes are all in ASCII format so that they can be edited by any standard text editor (there is no need to as long as youre using ElectriCalc). The first line of each database is a strange-looking string of characters that some spreadsheet users will recognize as a parsing string. You won't find it in this program and if you edit offline you don't need to mess with it. The second and third lines are the heading, and the others are the actual database entries. Feel free to arrange these data rows in any order that makes sense to you.

Access one of the databases by simply clicking a database button. Select a different choice by simply clicking the appropriate row. Holding down the right mouse button will show which data are associated with the database. The best way to enter new data in a database is to start with an existing entry that is somewhat similar to what you want. You can edit this data on the main screen and add it to the database by selecting Add on the database screen.

The List button prints a hard copy of this database. Remember, the actual database files (*.EDB) are readable text files.

The Sort button allows you to easily sort your data .

Clicking the Select button returns you to the main menu with your current selection. You can also double-click a selection. The Esc key returns you without changing the main screen.

This control enters the appropriate data on the main screen as a new line inserted after the highlighted line. If you modified data, e.g. Rm, on the main screen, you will get a new line that is identical to the line above except for the change(s). You can choose to delete that line or leave it intact.

Clicking the Delete button deletes the highlighted row. This row is saved in the Trashcan where it can be retrieved using Undelete.

This button gets you a listing of discarded data lines. Select the row you want to retrieve and click Retrieve (or Cancel if you dont want anything). ElectriCalc will stop you from retrieving data from the wrong database.

Data is normally edited on the main screen, but you can also change data or add comments using the Edit button. When you select this, a data window will appear. This mode allows you to edit the highlighted data line. If you select Update, your original line of data is retained, and your edited line is inserted after the original line. If you select Cancel, no new data will be added.


   Cells Database

The cells database (CELLS.EDB) characterizes Nickel-Cadmium cells.

CELLS  is a description of the selected cell (up to 20 characters). These cells are mainly Sanyo. The most popular are the N-1700SCRC and RC2000 for sport flying, and the KR-600AE and N-500AR for the smaller "Speed 400" models. This brand has a proven track record. Cells with an 'R' in the suffix are especially suited for the high charge and discharge rates needed for electric flight. Other cells have a higher energy to weight ratio but at the expense of higher current handling and/or charge rate

MAH  is the typical milliampere-hour capacity of a cell. This basically means that the cell can supply that many milliamps for one hour before the voltage drops substantially. This is generally higher than the manufacturer's rating, but will vary as a function of the charge method, discharge rate, and temperature. This number is used to estimate the motor run time at the calculated battery current. MAH is normally measured assuming a cutoff voltage of one volt or less. With high cell-count packs you can't afford to let the pack get down this low per cell without risking damage to the lower-capacity cells. You can expect the capacity of a higher cell-count pack to appear less due to the higher probability of a spread in cell capacities.

mOHM  is the equivalent cell resistance in milliohms. The lowest resistance is obtained with end-end soldered cells. Cell resistance should include the resistance of the cell interconnections.  The original data assumes minimal (end-end soldered) resistance. Bars or heavy braid will be somewhat more (+0.5 milliohm) and welded tabs could be substantially more (>1 milliohm). You can measure this yourself with a good DVM, ammeter, and load. Basically you need to measure under load and no-load voltage quickly so that chemical processes do not interfere. Use at least a 10-amp load. Cell resistance is voltage difference divided by load current divided by number of cells. See our web site for information on end-end packs.

DIA. & HGT.  are cell dimensions in inches and are informational only.

WGT.  is weight of the cell in ounces. This number is used in calculating the plane weight. When the cell type is changed, the plane weight is adjusted automatically.

MAH/OZ.  is informational. It is the capacity of the cell in MAH divided by the weight in ounces. Use this to appreciate the capacity versus weight tradeoffs that you must sometimes make.

COMMENTS  are allowed at the end of the line.

PTR  is a somewhat bizarre alphanumeric pointer assigned to this data entry for reference by the PLANES database.  There is a small chance that two entries will have the same pointer and thus "confuse" the program into selecting the wrong one.  This can generally be fixed by making a slight change in the description.


  Motors Database

The motors database (MOTORS.EDB) characterizes motors and gearboxes.

MFR  This is the manufacturer or reseller of the motor (up to 10 characters).

Description  is a description of the selected motor (up to 20 characters). Many of the European motors and the Aveox motors have a numbering system that describes the length and diameter of the motor. Unfortunately this standard is far from universal.

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 drillpress (hold the motor!) with a DVM connected to the motor leads. Run the drillpress and measure the DC volts from the motor (generator). Divide the drillpress RPM by the measured voltage. This should be done with neutral timing.

Izero  or 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, which characterizes the equivalent internal resistance of the motor. Rm is the most difficult motor constant to measure. You typically need to supply about 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. A battery pack with a load (power resistor or headlight) could supply the current. The motor timing does not matter, but shaft position can vary the reading. We like to take several readings while slowly rotating the shaft.

GEAR RATIO  is the number of revolutions the motor must make to rotate the prop one revolution. There is a gearbox efficiency number in the ecalc.ini file. You can change this by editing this file. ElectriCalc will not let you put unreasonable numbers here.

MM  is the magnet material (or an ingredient with a neat name). F-ferrite, C-cobalt, N-neodymium, S-strontium, ?-unknown. This is informational only and is not used by the program.

T/P  is turns of wire on each pole of the motor. This is informational only and is not used by the program.

COMMENTS  are allowed at the end of the line.

PTR  is a somewhat bizarre alphanumeric pointer assigned to this data entry for reference by the PLANES database.  There is a small chance that two entries will have the same pointer and thus "confuse" the program into selecting the wrong one.  This can generally be fixed by making a slight change in the description.


  Props Database

The props database (PROPS.EDB) characterizes propellers.

MANUFACTURER  is a description of the type of propeller and manufacturer (up to 20 characters).

K prop  is a propeller constant used in calculating the power absorbed by a propeller.  It indicates the manufacturer's generic prop shape and its effect on power. A prop with a higher K prop absorbs more power for a given diameter and pitch. This number is difficult to measure, and much of the data is empirical. However, there is substantial variation in prop factors (usually pitch) in what you buy which often overshadows the accuracy of other numbers.

K pitch  is a propeller constant used in calculating the power absorbed by a propeller.  It is used basically to compensate for the absorbed power consistently being less (or greater) than the equation would indicate based on the pitch as stated by the manufacturer.  A positive K pitch indicates that the power absorbed is less than the calculation based on the stated pitch.

K eff  is a coefficient to account for efficiency differences between props, e.g. 2- vs. 3-blade. This coefficient is new to Version 2. The coefficient Kpitch from Version 1 is still used but can only be changed with the database Edit function.

COMMENTS  are allowed at the end of the line.

PTR  is a somewhat bizarre alphanumeric pointer assigned to this data entry for reference by the Planes database.  There is a small chance that two entries will have the same pointer and thus "confuse" the program into selecting the wrong one.  This can generally be fixed by making a slight change in the description.


  Planes Database

The planes database (PLANES.EDB) characterizes planes and includes the cell, motor/gearbox, and prop database selections.

PLANE  is a description of the selected aircraft (up to 20 characters).

Wing  is the total wing area in square inches. Wing area is normally considered to include the area over/under the fuselage. The area of a wing with non-parallel leading & trailing edges can be figured by taking the width at the center plus the width at the tip and multiplying by the length (perpendicular to fuselage) from the center to the tip.

WGT  is the total aircraft weight in ounces. Don't forget to adjust the weight if you change motors. This weight should be appropriate for the number and type of cells you have entered, since the program adjusts the weight with cell changes. ElectriCalc is not ambitious enough to keep up with the weight of hundreds of motor/gearbox combinations (or the weight of different props for that matter!). A good rule of thumb for aerobatic sport planes is that the weight of batteries and motor should be about half the total weight.

DRAG COEF.  is an aerodynamic constant used in calculating the thrust required to move the plane through the air at a given speed. This number can be entered here or a reasonably good estimate can be quickly made by selecting C drag from the menubar. Wing struts and wires add a lot of drag. A good aerodynamics text is "Model Airplane Design and Performance for the Modeler" by Howard Chevalier. Reduction of drag in electric models is quite important. Biplanes in particular give disappointing flight times. Thick airfoils, fat fuselages, struts and wires should be avoided or minimized wherever possible. Remember that wing loading also contributes to drag.

PROP DIA.  is the propeller diameter expressed in inches.

PROP PITCH  is the propeller pitch expressed in inches. The number represents the number of inches the prop would advance if it were a screw in an inelastic medium. Pitch is normally measured at 75% of the distance from the center to the tip. The best pitch for most electric applications is between half the diameter (P/D=0.5) and the diameter (P/D=1.0). This assumption is used in some of the tools. Tip: try modeling a 6-10 pitch as an 8.5 or 9.0.

CELLS  is the number of cells in your battery pack. The most popular values are 7 and 10 cells. It is common to hook packs in series to make larger sizes. If you need to model two packs in parallel, create a new cell type with half the Cell mohm and twice the MAH and name it something like "2xRC2000".

ESC  is the equivalent resistance of the ESC (Electronic Speed Control) plus all the wiring and the connectors, fuse(s), and switch(es). The resistance of ESCs is a function of design and number and type of FETs. Also, brushless controllers have inherently higher resistance because they must switch both sides of the winding and this requires p-channel FETs with higher resistance. High performance brushless controllers have a bunch of FETs.

MTR CFG  is an alphanumeric representation of the motor configuration. Information cannot be entered directly here, but can be selected by clicking the raised panel or the Multi menubar selection. Two motors in parallel have same Kv, half Rm, and twice Io. Two in series have half Kv, twice Rm, and same Io. Etc, etc.

-pointers-  are 3-character alphanumeric constants assigned by the program to identify respectively the Cells, Motors, and Props database selections.  These constants are generated by the actual text of the database line.  Their purpose is primarily to allow all of the plane setup data to fit in an 80-column line. Not pretty, but it made things a whole lot easier to program. There is a small chance that two entries will have the same pointer and thus "confuse" the program into selecting the wrong one.  This can generally be fixed by making a slight change in the description.


  Printing & Saving Results

ElectriCalc allows you to print your setups or save them on your hard drive or floppy for future reference or to pass on to others. You can print up to 5 setups side-by-side to compare the effects of your changes. Select Print from the menubar or use the Alt+P shortcut key. This screen allows you to create printouts of the information you have created on the main screen . You can specify which column to put data in, move and swap columns around, print, save & retrieve this information. It looks complicated, but it's not hard and once you get the hang of it you'll find it really useful. If you want a quick printout of just the plane on the main screen, just select QuickPrint from the menubar or use the Alt+Q shortcut key.

These controls select the source and destination. 1-5 are the five printable columns, new is the data on the main screen, and temp is a hidden column to aid in shuffling data around.  Note that when you first enter this screen the From: is set to new and the To: is set to 1.

These buttons control the manipulation of columns. Move moves the From: data to the To: location. If you Move from one column to another, the From: column becomes blank. Swap exchanges the data in the two selected columns [Exception: data from the print menu never gets placed back in the main menu].  is placed in the new column. This tells ElectriCalc to print this column. You can set and clear these yourself by clicking them. When you print, blank columns are normally not printed (data is left-justified). If you want blank columns, simply click the appropriate [image]. Clicking New clears all columns of data. Otherwise the data does not go away.  It is saved when you leave ElectriCalc and read in when you return, but without any [image].

By clicking Print, the description column and all data columns with [image] will be printed contiguously. To save or retrieve data, click the File button. You can save the data on the print screen to a text file to be retrieved later or archived or shared with others. You will be asked to enter a file name. TXT is the default extension.  If you select OK or the Enter key without a filename, ECALC.TXT will be the default. You can retrieve data by clicking File when no column boxes are [image]. When you exit ElectriCalc, your last print screen is saved and automatically retrieved the next time you run. Note that no boxes are [image] for retrieved data.

Click Return to return to the main menu.  Remember that you don't have to select Print until you've accumulated all the data you want. It doesn't go away.


  Multiple Motor Configurations

ElectriCalc allows you to quickly configure multiple props and/or motors. You can specify up to 15 motors driving up to 15 props. There are no restrictions except that each motor must see the same load. You could drive 2 props from 1 motor or 2 props from 4 motors. You can choose a multi-motor configuration by selecting Multi from the menubar by clicking it, by clicking the raised Motor Configuration panel, or by using the ALT+M shortcut key.

First select the number of motors you want to use. The number of props will automatically change to the number of motors you select. If desired, now select the number of props you want to use. Finally, select the wiring layout you want to use.

Accept will transfer you back to the main screen with the new configuration entered there.

You can sort of understand the nomenclature if you read this as "4 props Ganged to 8 motors wired as Parallel units of Series strings of 2 motors."

Cancel will return you but leave the original configuration unchanged. The Esc key does likewise.


  Data Analyzer

You enter this screen with the controls preset based on the main screen selections.

 You can select a range of choices for number of cells, gear ratio, and prop diameter. The program will step through all possible combinations. Use the arrows to specify the ranges and step increments. Pitch automatically steps between D/2 and D. The titles in red are limits you specify. When the program makes calculations, it throws out any combination that is not within limits. ElectriCalc will show you the number of combinations you have selected. Don't worry about very large numbers. ElectriCalc will throw out all but the Top 10 in each of 4 performance categories.

Click the Analyze button to start crunching numbers. ElectriCalc will continually estimate your computing time. If you want to quit, simply press the Esc key.

As ElectriCalc makes its calculations, you will see the estimated time remaining, how many combinations have been tried, and how many passed the selected limits.

When ElectriCalc completes its calculations, a List screen will appear. This list will have up to 40 setups. ElectriCalc selects the Top Ten in the categories of Cruise Time , Top Speed , Climb Rate , and Climb Height . You will get less than 40 setups if:

 - You started with less than 40 combinations.

 - Less than 40 are within limits.

 - One or more setups are in the Top Ten in multiple categories.

You can print this list, save it in a text file, or sort it by up to three categories. You can select a particular setup by clicking its row in the list. This will enable the Select button. You can also double-click the row to both select and return. Select will transfer you back to the main screen with the new setup (prop, gearing, cell count) entered there. Cancel will return you back to the Analyzer screen.

Return gets you back to the main screen.


  Estimating Coefficient of Drag

You can quickly estimate the coefficient of drag Cd by selecting Cdrag from the menubar by clicking or using the Alt+C shortcut key.  Click the appropriate dots [image] for your plane.  Feel free to modify the number you get. Of course you can enter a calculated number directly.

If you select Accept, you will return to the main screen and the coefficient you just estimated will be placed in the Cdrag text box.

If you select Cancel, you will return without changing any data.


  Working with Graphs

There are two kinds of graphs available. The Prop Selection graphs (by Current, by Gearing, by Cell Count) are useful tools for selecting components. The Thrust & Drag and System Efficiency graphs are useful for understanding thrust, drag, and power losses.

You can Print any graph along with descriptive data by simply clicking this button. If you print in Landscape, you will get a larger graph without the data.

The Return button gets you back to the main screen. The Esc key does the same.


  Prop Selection Graphs

The 3 prop selection graphs are truly unique. Once you grasp the concepts, you will find them to be useful tools. The two axes are diameter and pitch. The red lines represent D vs. P for a fixed current. If you think of each intersection of green lines as defining a prop size, you can easily see how much current it should draw. The solid blue lines are boundaries based on best motor efficiency. You can change the range by simply entering a new max value in the AMPS text box. The right-most dashed blue line represents P=D. The other is P=D/2. The X represents your prop selection on the main screen. If you point your mouse cursor near a green-line intersection and click, the X will move to the nearest intersection.

If you click the Select button, you will return to the main screen with the prop size specified by the X. Now comes the cool part. If you click the mouse while holding down the Ctrl key, you will create dots that 'snap' to the grid. Ctrl-click a dot to remove it.

If you click the List button, you will get a list of the performance of all the props you selected! You can print this list, save it in a text file, or sort it by up to three categories.

 This is the current used to construct the graph. On the Current graph shown below, it is the maximum current, and the minimum is half of this. The program makes a guess at this number and you can change it in the text box.

The three prop selection graphs are used in the same manner with a few exceptions. The Gearing graph below has curves representing different gear ratios with the indicated current. It otherwise works the same as the Curent graph.

The Cell Count graph below has curves representing different cell counts with the indicated current. It works similarly to the other two graphs with an important difference. If you click your mouse to move the X, the graph will redraw itself by assuming the nearest integer cell count and recalculating current accordingly.


  System Efficiency Graphs

This graph simply shows you where your power is going. If the motors had gearboxes, there would be an additional slice for this loss. You can print this graph along with descriptive data by simply clicking the Print button. If you print in Landscape, you will get a larger graph without the data. Return gets you back.


  Thrust & Drag Graphs

This graph shows how thrust and drag vary with speed. Generally, thrust decreases with increasing speed. It drops off dramatically above pitch speed . The point at which thrust and drag are equal determines top speed . The steep slope of the left side of the drag curve is below stall speed and is due to the increasing angle of attack. The right half of the curve is due primarily to parasitic drag, which increases as the square of the speed. Occasionally these curves intersect above stall speed. This is a big clue that you might have a candidate for a bungee launch! The two dashed lines are reference curves. They represent props with P=D and P=D/2 with D chosen to draw the same current as your prop. The prop with the highest apparent static thrust has the poorest performance at normal flying speeds. Commit this picture to memory! You can print this graph along with descriptive data by simply clicking the Print button. If you print in Landscape, you will get a larger graph without the data. Return gets you back.


Shortcut Keys
  Shortcut Keys & Other Secrets

The main screen has several shortcut keys. An item on the menubar can be selected by holding down the Alt key and pressing the underlined letter. In addition, you can access the Multi menubar selection by clicking on the raised Motor Configuration panel. A database button can be selected by holding down the Ctrl key and pressing the capital letter or s for planes. When the focus is in a text box, the + and - keys increment and decrement the value.

Entering data into AMPS will cause the Diameter , Pitch , and Gearing text boxes to "light up."  Double-clicking on one of these will calculate the value needed to produce the current you entered. Simarly, entering data into Wing Load will cause the Plane Wt. and Wing Area to "light up."  Double-clicking one of these will cause it to be recalculated.

Holding down the right mouse button on a database button "lights up" the text boxes stored in that database. For Planes, the other databases are lit in different colors.

A single click of QuickPrint gets you a printout of most of the data you're looking at.

This Help program can be accessed directly with the F1 key. It is context-sensitive.

When you stray from the main screen, the Esc key will generally take you back to the previous screen.


  Typical Resistances

Add 1 milliohm per connector contact pair (not Tamiya!).

Add 1 milliohm for good switch.

Add 2.3 milliohms for 30A fuse.

Add 4.5 milliohms for 20A fuse.

Add 1.3 milliohms per foot for #10 wire.

Add 1.5 milliohms per foot for #11 wire.

Add 1.8 milliohms per foot for #12 wire.

Add 2.3 milliohms per foot for #13 wire.

Add 2.9 milliohms per foot for #14 wire.

Add 3.6 milliohms per foot for #15 wire.

Add 4.5 milliohms per foot for #16 wire.

Add 7.2 milliohms per foot for #18 wire.

Add 1.5 milliohms per foot for 4.0 sq. mm. wire.

Add 2.4 milliohms per foot for 2.5 sq. mm. wire.

Add 4.0 milliohms per foot for 1.5 sq. mm. wire.

Check your data sheet or manufacturer for ESC resistance.


  Sorting Data

You can sort databases as well as lists generated by graphs or the analyzer . You can sort by up to 3 categories (columns). Clicking on a list button [image] reveals a list of the column names. Select the column you want to sort.

If a column only contains numbers, it is sorted in numerical order. Otherwise it is sorted alphanumerically. This means 10 comes before 2 in a column that contains letters as well as numbers. Choose ascending or descending order by clicking the appropriate dot(s) [image].

Sort will sort according to your choices.

Cancel will return you to your (unsorted) list. The Esc key serves the same function.


  Odds & Ends

The File menubar selection is where you go to backup, restore, or  merge database files, view your trashcan file, setup your printer(s), and exit ElectriCalc.

You can back up databases by selecting File from the menubar and then selecting Backup Files. This utility will allow you to backup one or all of the databases at once. The databases are backed up automatically at appropriate times, but you can choose a manual backup at any time. Backup files have extension EBK.

 You can restore databases by selecting File from the menubar and then selecting Restore Files. This utility will allow you to restore one of the databases or all databases at once from the corresponding .EBK file.

You can merge data external to the program by selecting File from the menubar and then selecting Merge Files. This utility will allow you to extract database information from other files.  The intended use is to allow the sharing of information with others. Another modeler can give you the information he's collected with his program and this utility will add it to your database. It will not add duplicate information or data that is improperly formatted. The merge function allows you to take a text file (like e-mail) that contains lines of ElectriCalc data, and automatically extract the data and place it at the end of the appropriate database. Use this to get new data from the ElectriCalc web site .

 You can throw out the trash periodically if you're that kind of person.

 Select or configure your printer(s) here.

If for some reason you should ever want to quit playing with ElectriCalc and get on with your life, it can be done,  You can exit by selecting File from the menubar and then selecting Exit. You can also use the Ctrl+X shortcut key from the main menu, or use the usual Windows clicks.

The Preferences selection on the menubar allows you to choose Metric or English units, and what level of annoying messages you are willing to tolerate.

ElectriCalc will display either English or metric measurements. Props are traditionally in inches in either system. ElectriCalc will warn you if you do things that will cause you to lose data you have entered. If you find these annoying, you can turn them off with ?Changes?. ElectriCalc will prompt you for printer information at appropriate times. You can turn them on or off with ?Printer?.

This is where the Help file can be accessed. This is also where the version number & copyright stuff is located. Our Internet address is also here.

Finally, ElectriCalc is universally called "ecalc" so if you hear or read about ecalc, they're talking about this program.


  References

The following books were invaluable in the development of ElectriCalc and are highly recommended:

Electric Motor Handbook  by  Bob Boucher.

Model Airplane Design and Performance for the Modeler  by Howard Chevalier.


  Shoo-fly Pie

Shoo-fly pie is the official food of electric flyers.  The following is a recipe for shoo-fly pie if you would like to give it a try:

     3/4 cup dark molasses

     3/4 cup boiling water

     1/2 teaspoon baking soda

     1/4 teaspoon salt

     1-1/4 cup sifted all-purpose flour

    1/4 cup butter or margarine

     1/2 cup firmly packed brown sugar

     pastry for a 9" unbaked pie crust

Mix first 4 ingredients.

In a separate bowl, mix next 3 ingredients with your hands.

Pour about 1/3 of molasses mixture into pastry-lined pan.

Sprinkle with 1/3 of flour mixture.

Continue alternating layers, ending with flour mixture.

Bake in pre-heated oven at 375 degrees F. for 35 minutes or until firm.


ECALC.INI

.INI files are used to store initial values of variables, preferences, and other configuration data.


ElectriCalc Web Site

www.SLKelectronics.com/ecalc


motor constants

The ideal motor model uses three parameters; Kv, Rm, and Io. These are measured with the motor timed neutral, and assume the motor is then optimally timed for the application.