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Aug 17, 2007, 05:41 PM
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WeboCalc - Free software for choosing motors - Part III


Hi folks, thought I'd move the current WebOCalc thread here as it will help me keep the discussion on topic and maintain a friendly, courteous, and cooperative atmosphere on this thread.

The previous WebOCalc thread was here:
https://www.rcgroups.com/forums/showthread.php?t=558396

To get this ball rolling and (re) introduce WebOCalc, here is part of my first post from the previous thread:
Quote:
Hi everyone, some of you may have run across WebOCalc before. It's a little Javascript program I wrote to help design ones own planes, and this forum seems like the right place to introduce the newest version.

WebOCalc was written from the start with three goals in mind: it had to be very easy to use, it had to work on your computer whether you use Linux, FreeBSD, Mac OS, or Windows, and it had to be Free as in freedom (Free software, like Linux or Firefox). It also works whether you live in the USA and are stuck with imperial units, or whether you live elsewhere in the world and use metric units.

If you enter a few numbers into WebOCalc (things like wingspan and chord, the weight of your model, the battery voltage, and the desired current draw), the program will tell you how the model will fly, in simple English. It will also suggest some propellers that will work with the model, and appropriate gear ratios matching each propeller. For direct-drive, pick the propeller(s) with a gear ratio near 1.0.

All this means you will know before you build if your plane is going to be too heavy, too small, lacking in power, etc. You will know if you need a bigger battery or bigger motor, and you will know which propeller to use.

WebOCalc lets you specify your desired pitch speed for the model, if you already know what you want and what the model needs. At the same time, if you want, WebOCalc can suggest a pitch speed for you. This is very handy for quickly getting a model in the air, or if you have no idea what a good pitch speed for the model might be.
You can get Webocalc (currently at version 0.8.8) at http://flbeagle.rchomepage.com . Click "Software", then "WebOCalc".

-Flieslikeabeagle
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Aug 18, 2007, 05:53 AM
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glen's Avatar
just saying hi and thanks for the new version.
Glen
Aug 18, 2007, 09:57 AM
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Quote:
Originally Posted by glen
just saying hi and thanks for the new version.
Glen
You're welcome, Glen! I just realized that WebOCalc does not contain the APC 10x10 "E" prop (I recently got one from EcubedRC.com), so I will probably release a new version very soon.

I also found a way to calculate the average prop thrust over the entire speed range (from static all the way to pitch speed), and it is very illuminating to compare both the static thrust and this average thrust and see how they differ from prop to prop. The high P/D props (like that 14x12 you were using) do much better when it comes to average thrust over a range of speeds, which goes some way towards explaining the longer flight times you get with them.

Thanks for stopping by!

-Flieslikeabeagle
Sep 12, 2007, 02:13 AM
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Swissflyer's Avatar
Hi FB,
Just to let you know I dropped by. The new version is nice – thanks.
Mark
Sep 12, 2007, 07:10 AM
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glen's Avatar
Flieslikeabeagle
Are you still thinking about adding the average prop thrust into the sheet.
Would be very cool.
Cheers
Glen
Sep 21, 2007, 09:08 PM
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Glen, yes indeed. Remember I mentioned I had a surprise? Well, the surprise is now out - I wrote a second program, PowerCalc, that is yin to WebOCalc's yang. PowerCalc is intended to eventually be much more accurate than WebOCalc, the downside being it's also considerably harder to use. But everything I learn from Powercalc will end up back in WebOCalc in simplified form one day.

In Powercalc, I've implemented calculation of (a) static prop thrust, (b) average prop thrust over the entire speed range from 0 mph up to the pitch speed, and (c) prop thrust at the actual pitch speed itself. I think (b) in particular will be very handy for estimating real-world in flight performance; I could modify it to calculate the average thrust from the models stall speed up to the pitch speed instead, which might be even better for predicting in-flight performance.

Dunno if you'd be interested in Powercalc, but if you feel like taking a gander, it's at the same place: http://flbeagle.rchomepage.com, click "Software", click "Powercalc".

Known bugs/issues:

1) For the moment, Powercalc uses a very simple propeller simulation, which is less accurate than the one in WebOCalc. The predicted motor performance (efficiency curve, heating, etc) should be accurate, the predicted actual current with a given propeller will probably not be too exact until I find time to write code for a better propeller model.

2) There is a little bug in the code that shows ESC + motor heating in the red curve on the graph (instead of motor heating alone). I will fix this as soon as I find time and enthusiasm for the job...)

-Flieslikeabeagle
Sep 24, 2007, 04:57 AM
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Swissflyer's Avatar

Nice surprise


Thanks FB,

I like the graphical output & now I can check out the gearboxes that I have in stock

Here is first pass on my recently modified Saab Gripen brushless in-runner parkjet. The graphical output tells immediately that I have some “headroom” for pushing the set-up a little further.
First I will do some flight tests with what I have, then let you know how I get on.

Mark
Sep 24, 2007, 12:13 PM
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Quote:
Originally Posted by Swissflyer
<snip>now I can check out the gearboxes that I have in stock
I thought you'd like that, since it's a feature you've asked about on the WebOCalc thread.
Quote:
Originally Posted by Swissflyer
The graphical output tells immediately that I have some “headroom” for pushing the set-up a little further.
Right, that was the idea exactly - now you can see whether you are underutilising your motor, overutilising it, or using it optimally. The goal is to operate the motor (at full throttle) a little above the efficiency peak, so that in flight the motor operating point is centered around the peak efficiency location. If you operate the motor at peak efficiency at full throttle, then it will spend most of the time operating at less than peak efficiency unless you fly full throttle all the time.

I started writing Powercalc back in 2004, and at that time I did not know of any other motor sim software which gave you these motor performance graphs to tell you at a glance where you were operating the motor. Since that time there is the very nice PeakEff software which does somewhat the same thing (though it uses three motor constants rather than the four in Powercalc, and does not include motor heating either, AFAIK).

I had some online discussion with Matttay, the creator of PeakEff back in 2006 when he first announced it - I showed him PowerCalc, and we had a little discussion about both pieces of software. He also dropped into my "four motor constants model" thread, but decided the small improvement in accuracy wasn't worth the fairly large increase in code complexity in the software.

Here's the post where I first told Matttay about Powercalc:
https://www.rcgroups.com/forums/show...postcount=1426

-Flieslikeabeagle
Sep 25, 2007, 08:35 AM
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Swissflyer's Avatar

Definitely


Quote:
Originally Posted by flieslikeabeagl
The goal is to operate the motor (at full throttle) a little above the efficiency peak, so that in flight the motor operating point is centered around the peak efficiency location.
Hello FB,

Exactly, then you can take it a step further as your LiPo can be smaller, lighter (cheaper) for a given flight performance so you get a weight saving / cost saving advantage as well

Mark
Mar 31, 2008, 05:12 AM
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glen's Avatar
G'day mate. Things been pretty quiet around here???
Just poping in to try your calcualtor again for a friend.
I'll get back to you in a couple of weeks about how it goes.
Cheers
Glen
May 10, 2008, 03:02 PM
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Hi Glen,
Right you are, I haven't done much work on WebOCalc of late...been too busy flying, building, earning a living, or hanging out with my wife!

I've also been dealing with some RSI problems in my hands, so I'm on the computer as little as possible these days. That has kept me from doing much programming of late.

I do have several ideas to improve WebOCalc, and hopefully one of these days I'll start to implement some of them.

Nice to hear from you again!

-Flieslikeabeagle

P.S. I was recently able to get Scorpion Calc (Windows executable) running on my Linux box, and that let me compare WebOCalc and Scorpion Calc. Keep in mind Scorpion Calc uses very sophisticated internal modelling of the motor, including heating, eddy current losses, etc, while WebOCalc is intentionally based on the simplest mathematical model that captures the essentials.

So what did I find when I compared the two? If you put the same battery voltage into both, and use the correct motor efficiency in WebOCalc, the results from both calculator programs agree within a few percent for all the combos I tried.
May 10, 2008, 07:22 PM
Registered User
glen's Avatar
Morning.
We tested his plane about 7 days ago and the prop was spot on.

Can't ask any more than that!
We just had to put a bigger battery in so he could get rid of some lead ballast.
Cheers
Glen
May 10, 2008, 08:49 PM
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Glad to hear WebOCalc worked well for your friend, Glen! Actually that's part of the reason I haven't been too motivated to work on WebOCalc much of late - it works pretty well already if you know how to use it!

The improvements I have in mind are primarily to make it even easier to use. I received feedback from at least one person who was stumped when he tried to use WebOCalc because he had no idea what sort of numbers to enter for motor Kv, battery voltage, or current draw per motor. So I would like to come up with some way to make it easier to get at least an initial set of numbers into the program for a first pass.

-Flieslikeabeagle
May 11, 2008, 05:39 AM
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glen's Avatar
My question regarding your work at the moment is it easily found now it's in a blog?.
I for one never go into blogs and would never have found this. Yes I do remember your reason for coming here. Haven’t noticed any of his posts elsewhere.

I agree totally. If it aint broke don't fix it. I just think with its unique angle of approach it should be readily found. Too good to hide away.
Cheers
Glen


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