EffXL Ver 1.00

An accurate motor efficiency calculator

by Rod Badcock

Spurred on by the prop data measurements made by Hyperion for their Emeter and made available at Aircraft World I decided to build on the success of ThrustXL ver 1.02 and now EffXL is here! This development could not have been made without the data contributors at RCGroups and Aircraft World.

The data used to build the database is from painstaking dynometer measurements arranged by Hyperion. This database allows the easy measurement of motor efficiency from three simple measurements for a given prop:

Of course those of the recommended measurement tool is the Hyperion Emeter available from Aircraft World that allows all of these measurements simultaneously in one instrument and will even perform these calculations for you!

Please download the MS Excel file from here - but check back often as I will add to the database of props as measurements are completed.

Why do I need EffXL?

How do you know what is the optimum prop selection for the motor you have? Traditionally you could either rely on manufacturers data for a small selection of props or invest substantial time and money in a motor dynamometer. Using this spreadsheet and simple (cheap) hand-held instruments you can characterise motor efficiency for most common propellors.

This calculator allows a close to optimum prop selection for a given motor and power system without the need for dedicated measurement equipment. This allows an optimum efficiency of operation to be chosen, and one can at least have a conservative flight system which won't result in instant melt-down, and can then be tweaked for optimum performance.

The program

The Spreadsheet has a single worksheet user interface that allows selection of propellor and entry of the measured RPM, current and voltage.

The user interface is quite simple and requires input in two areas; selection of the prop type and RPM range from the drop-down box and entry of the measured RPM, voltage and current for that prop. From this data a graph is produced of the pitch speed of the prop and mechanical power required to turn the prop in the RPM range.

The program then predicts the efficiency for the prop, measurements and RPM.

Two additional worksheets are used for this window: 'Data' contains the prop and coefficients database, and 'Storage' contains the predicted curve data.

Well I hope that is of use to anybody - it has certainly become a useful tool for myself.


DOWNLOAD Program File here: EffXL.zip