Drive Calculator Version 2.21

This is probably one of the best, and most complete, set of motor analysis tools that I have seen. Based around a Microsoft Excel spreadsheet This includes a propeller thrust and power database, in a similar form to MotorXL, a motor database, and tools for predicting home made motor performance. With these tools it is possible to predict the performance of motor and prop combinations - even with custom motors!

The software requires Microsoft Excel (or compatible) and can be downloaded from Drive Calculator V2.21.

This drive calculator determines the approximate characteristics of an electric motor from a few measured data points and computes the operating point for the selected propeller. See hints for the operation under "help" on the top right on the sheet "Calculator". Measured motor data, propeller data, and transmission data are registered in expandable lists on sheets "Motors", "Props", and "Gear boxes". Please read the guidance for supplementing further data base entries on these sheets. These tools will produce efficiency and power plots for the motors:

The drive calculator is a Microsoft Excel application. In Excel 'Tools' > 'Options' "iteration" must be activated. The number of the iteration steps can be limited to 100, accuracy to 0,1.

How do I use the software?

The most basic way of using the calculator is to use elements from the database (prop and motor). These can be selected from the drop down boxes to define the motor type, gearbox and prop. An operating voltage should then be selected and the graphs can be produced. This screen is shown below:

Then motors can also be cross-compared in a similar fashion in the 'comparison' sheet. Just select the motor, gearbox, and voltage and the efficiency graphs for the motors will be compared:

There are a selection of tools under the 'tools' sheet that are invaluable for the motor designer / builder. These will allow prediction of the motor characteristics and performance if the stator and magnet geometry is stated:

The minimum data necessary for the motor calculations are the no-load voltage and current, as well as voltage, current, and speed at two operating points under strongly different loads (small prop, high rpm, small current - large prop, low rpm, high current). The operating voltages should not differ by more than 20%, if possible.

The accuracy improves if the idle speed is measured. Then the unloaded data should also be registered as the first load operation point. Accuracy improves even more, if further measurement points are added. This can be a second unloaded operating point at a different voltage or a further operating point under load. The most precise results will be achieved by providing data for two complete unloaded measurements (inclusive rpm) and three measurements under different loads - best if one of these is with zero-load, thus in the no-load operation.

The computation is based on a simplified model of the DC motor and is applicable to brushed motors and brushless motors. But do not expect miracles, since the model does not consider all factors , i. e. the interaction of the ESC with the BL motor.

Even if careful measurements with good equipment are taken, the calculator results may sometimes deviate substantially from reality. As a check the difference between the measured and computed current values are indicated under "I-Diff.". However, if only two rpm values are provided, the calculator cannot compute a meaningful "I-Diff." indication and it will not be displayed.

If differences of more than 3% arise, you should examine the measured data and repeat the measurements, if possible, or select alternative data (with different voltages or loads). The calculator is particularly sensitive to discrepancies in the no-load data.

Please perform the unloaded measurements at operating temperature. The quiescent current of the ESC must be subtracted from all current data. While not more than five data records can be registered in the "Motors" list, it is advisable to do some additional measurements in order to have alternative data ready.

The results of the propeller computations can also deviate substantially from reality. This depends particularly on the provided data being accurate, which have been collected from various sources.

Anyone making motor or propeller measurements should make their results accessible for other users. Please make use of the mailto-links on the sheets "Motors" and "Props ". Continuous data base updates will be provided on www.elektromodellflug.de/datenbank/.

Please send error reports, hints, and criticism to Christian Persson (cp@ctmagazin.de).