Mac OS X Motor Performance Utility - Page 2 - RC Groups
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Sep 17, 2004, 01:28 PM
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Originally Posted by macr0t0r
Not a bad program. May I make a request? Aallow me to specify volts per cell. Having to convert LiPo cells' voltage and internal resistance into NiMh values is a little tiring.

Are you sure you should auto-calc .75r angle? This will vary from prop to prop, so you may want to let the user override the default value (perhaps a checkbox stating "auto-calculate generic value").

Nonetheless, this is excellent work with a clean interface. It'll help me narrow the field as I try to engineer the next powerplant for my project. I REALLY like the ability to calculate estimated values at a given airspeed. Thanks!
Thank you for the feedback and the suggestions! I believe opening up the voltage value to the interface will be beneficial. However, I don't know how the voltage drops as a function of current for LiPo chemistry. Do you know of a source for that data? I have not used LiPo cells (yet).

On the prop blade angle: the NACA data are based on this angle, so I can't get away from it entirely. It is calculated based on blade diameter and pitch. I can open up the field, and calculate pitch based on the angle, if that would help. But I'm not sure what you mean by a 'generic value'.

I'm glad you like the airspeed variable, although I admit it is a little difficult to think in terms of feet per second. The ultimate plan is to allow a user to enter a range of values so that thrust and power can be calculated and compared over an entire range of flight conditions.
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Sep 24, 2004, 04:06 PM
Got more toys than my kid
macr0t0r's Avatar
Bug report! Your application will fail to converge ("Rats!") if the solution will give a battery current of 10amps or above.

Would you be willing to post some of the equations? I have yet to find a consolidated thread with these equations, and the search is getting tiring.
Sep 24, 2004, 07:36 PM
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It shouldn't be the amps, but some other combination of inputs. For example, if you input a very small battery with a huge direct-drive prop, that could cause this message. A future version of the program may wait until all numbers are entered before attempting to calculate the steady-state values. That was the original thought in the "Calculate" button, which is not needed right now since calculations are performed at every input.

Can you email or post a screen shot so I can see the values you're using?

On the subject of posting equations: I hadn't thought about doing that per se, but I plan on documenting the consolidated list of references (books, periodicals and papers) that were used in the development of the program. From these, a user could see the specific equations that are used.
Sep 25, 2004, 12:56 AM
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I can tweak a variety of numbers until ESC or Battery current reach 9.99amps. As soon as I tweak any number (cell-count, prop, reduced resistance, etc), then it fails.

Errr...Screenshot later when I get back to my Mac.
Sep 25, 2004, 02:04 AM
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I definitely would like to see the data - I'm sorry it is not working at the flight condition you want to evaluate. In the mean time, here's an example of a scenario with more than 10 amps being drawn from the battery:
Sep 25, 2004, 04:33 AM
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Dear Craig
I will give it a try
Sep 26, 2004, 12:14 AM
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Ah ha! It only fails if the Gear-Ratio is set to EXACTLY 1.0, then it will barf on anything 10 amps and over. It works as soon as the gear ratio is set higher than 1.0.
Sep 27, 2004, 01:15 AM
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Thanks, macr0t0r

That's helpful info - I'll take a look at why things break down for direct drive at 10 amps. Thanks for your troubleshooting!
Nov 02, 2004, 11:56 PM
Registered User

AMP 0.2.0 Released

I've just uploaded the 0.2 version of AMP to the site The new point release adds a few features but doesn't address the convergence problem .

New features:
- motor selection via pop-up menu (user configurable)
- voltage per cell
- simulate BEC current drain
- auto-calculate selection

Please let me know what you think. Enjoy!
Nov 03, 2004, 02:38 AM
Got more toys than my kid
macr0t0r's Avatar
Not bad! Definitely an improvement. A few comments:

The good stuff:
(1) Really like your implementation of a motor library. Simple and easy to use.
(2) Thank you for allowing me to specify my own battery parameters. I can finally simulate LiPo cells!
(3) I'm glad you added the ability to turn off auto-calculate. This helps prevent me being driven mad by the "cannot converge" error at every field.

Request Improvement:
(1) Not all props are created equal. Somehow, I need to be able to specify a "prop constant" of some sort. An APC 10x6SF, APC 10x6TE, GWS 10x6RS, and GWS 10x6HD all have different thrust, RPM, and load. I have no idea what kind of prop your simulation is geared for.
(2) Could you have it display output voltage of the pack after the load is applied (taking account of internal resistance and current draw)?
(3) Can you display the "input" watts and the ratio of input/output watts to rate efficiency.
(4) That dang convergence error is still there (as you know). However, I can work around it well enough for now.

The battery stuff is now sorted, so the only thing I truly need now is the prop-constant so that I can match this program to my real-world measurements. The Watts and Voltage is just icing, really. In any case, you did and excellent job on this program. Thanks!
Nov 03, 2004, 10:57 AM
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I think he mentioned .75 as the prop constant. On the GoBrushless simulator they use this for GWS HD props, I believe.
Nov 03, 2004, 11:42 AM
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Well, that explains the high RPM I'm getting, then. The problem is that many props have different widths and slightly varying "pitch layout" from root to tip, so different brand/type props of the same size act very differently. The prop constant, if I'm not mistaken, mostly takes the prop-width in account. In any case, I just need to find a way to adjust the prop performance so that it matches my real-world tests. Then I can use this utility to make reliable predictions.

Still, this is looking good, and still permits me to make ballpark figures.
Nov 03, 2004, 12:32 PM
Registered User

Propeller model

As indicated in the 'read me' file, AMP currently uses NACA TN 698. Although the data for several propeller blade aspect ratios were presented, AMP currently uses only one, which constrains the aspect ratio of the model.

Bob Parks has recommended Mark Drela's 'qprop' algorithms for higher accuracy. I will hopefully provide the option of either TN 698 or qprop in a future release - it all depends on the amount of time I can dedicate. The higher accuracy of qprop, however, comes at a price: quite a bit more propeller-specific data is required to get started. Like the recent addition of the 'motors.txt' configuration file, I will probably ask for user submissions of data so that everyone can share each other's labor.

By the way, another diversion from AMP is a little program that I hope to release shortly called 'ZlogX', a Mac OS X interface to the Zlog alitimeter produced by Hexpert Systems ( Anybody interested in that?
Nov 03, 2004, 01:04 PM
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I'm more interested in the newer prop model, truthfully. qprop seems a bit overkill, but I suppose it is more accurate than using a prop coefficient if you don't have experimental data on the prop series.

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