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Old Jun 04, 2002, 10:14 AM
Mitch G's Avatar
Naperville, IL USA
Joined Nov 2000
1,886 Posts
How about a power system database?

I was wondering if it would be possible to create a database in which MEASURED setups could be input by folks for other folks to look at. It would be like a reality-based e-calc type of thing. Call it: real-calc.

The required fields for each record would be:

Motor Make (e.g. Graupner, Mega, Jeti, Hacker, etc.)
Motor Model (e.g. sp400, 22/30/3, B40-8S, etc.)
Gearing (if any) (e.g. none, 2:1, 4.6:1, etc.)
Prop Make and Model (e.g. APC-E, APC-Slow, Graupner CAM, etc.)
Prop Size (e.g. 12x8, 14x7, etc.)
Number of cells
Make of cells (e.g. Sanyo RC2400, Panasonic 3000, etc.)
Type of cells (e.g. NiMH, NiCad, Li, etc.)

Then, at least one (if not more) of the following fields would have to be populated:

MEASURED current
MEASURED RPMs
MEASURED thrust


Over time, the E-zone would have a nice, centralized database of real-life information. This would be great info if thinking about a given setup that's in the database. But, it would also be helpful when using calc programs to see how they compare to real life and then use that information to "refine" other calculations.


Mitch
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Old Jun 04, 2002, 11:28 AM
RIP Ric
Andy W's Avatar
Marietta, GA
Joined Jun 1999
43,312 Posts
Measured? Where, in flight? Not many of us are able to do that.
Static tests don't really mean anything.. so the data would be of little use.
As far as in-flight performance, there are so many combinations, the DB would be huge. Fortunately there are at leat two commercial software packages (motocalc and electricalc) that can compute everything for us, and, despite the complaints, they both do a great job of predicting power and thrust at particular airspeed (which DOES matter) for every motor, cell, GB and prop combo you could come up with. The prediuctions are accurate to within a few % - limitations include GB losses and prop factors, which are not accurately measured and vary from system to system. There are also free versions - online web databases, that are not as flexible, but certainly able to provide the info. you are looking for - PCalc from Diverity Model Aircraft is just one example..
It's more interesting for members to post their power system experiences along with the models they used them in - in the gallery would be a great place to do this - I try to include this information in my own "gallery" page of model - click on the www link below to see what I mean.

..a
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Old Jun 04, 2002, 01:55 PM
Mitch G's Avatar
Naperville, IL USA
Joined Nov 2000
1,886 Posts
First of all, I meant static measurements. I figured most of us have at least a Whattmeter and many of us have tachometers as well. I also bet that most of us take current and RPM measurements when we install a new power train in a plane. So, I figured, why not provide a place to centrally store this wealth of knowledge.

I'm aware of the calc programs and use Motocalc a great deal. In fact, it is my experience with these programs that further supports the need for real world, measured data. For example, I've seen discrepancies between measured current and predicted current on the order of 20% (21A predicted vs 26A measured). So, just having data about the current draw of a setup would allow me to refine my interpretation of the calc program output. And, I figured, if the user is also able to provide RPMs and in the rare case thrust numbers, this would help folks even more. Furthermore, having a database as such may help the calc program developers refine their algorithms, which would only benefit us e-filers all the more.

My bottom line is that real world data is always useful even if it is not the complete picture.

As far as how much disk space such a database would require - I leave that up to the E-zone management to ponder as part of their benefit-vs-cost decision regarding this suggestion.


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Old Jun 04, 2002, 10:08 PM
RIP Ric
Andy W's Avatar
Marietta, GA
Joined Jun 1999
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Disk space would not be an issue.
..a
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Old Jun 04, 2002, 11:01 PM
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jbourke's Avatar
United States, OR, Corvallis
Joined Nov 1998
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I think its a neat idea. Its actually on the to-do list, but in a slightly different format than envisioned here.

We don't have a problem with disk space or anything like that. The real issue is money. I don't have the free time to devote to custom coding on the site right now, so I would have to contract someone out. This is expensive, so I reserve that for when we have a pressing need.

Jim
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Old Jun 04, 2002, 11:35 PM
Mitch G's Avatar
Naperville, IL USA
Joined Nov 2000
1,886 Posts
Thanks for the response. I'm glad to see the basic idea is already on the to-do list. But, I understand the need to prioritize.


Mitch
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Old Jun 11, 2002, 01:47 PM
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Old Jun 14, 2002, 12:42 PM
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Joined Apr 2001
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As Andy pointed out, the static measurements are of relatively little value in telling you about the in flight performance. Props can vary quite a bit, and you'd also need to record temperature, humidity and altitude if you are going to compare thrust.
The reason the calcs are so useful is that there are thousands of combinations of props, batteries and gear ratios for a single motor. High static thrust is a very poor way to choose among them.

There have been a number of compilations of "What Works" -- combinations of gear in successfully flown planes.

http://members.aol.com/KMyersEFO/page38.htm Good and bad.
http://www.slewin.clara.net/elec/sfreviews.htm
http://home.ptd.net/~rcm65/whatwork.html

Rick.
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Old Jun 18, 2002, 02:06 PM
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No Response...

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Old Jun 18, 2002, 02:36 PM
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jbourke's Avatar
United States, OR, Corvallis
Joined Nov 1998
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Re: No Response...

Quote:
Originally posted by Arbo
I guess I'll have to take a lack of response as a negative.
Sorry about that. Sometimes I just don't pay attention very well. Due to "thread drift" I sometimes tune out of discussions and miss important things. You should post a new thread to get my attention.

I'd love to have your help. We use PHP and Mysql extensively. If you are familiar with those tools you can dig in during your free time.

I have to get to know you a bit before you can have access to our servers, though.

Jim
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Old Jun 18, 2002, 06:37 PM
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Static test are a good way to compare different setups. You can also take things into consideration and use your experience to infer how it will behave in the air.
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Old Jun 18, 2002, 08:35 PM
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Jim...

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Old Jun 18, 2002, 09:54 PM
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I think a good idea would be predefined selections for the components with an 'other' box you can fill in if you have something odd. Also predefined selections for the measurement unit, so that you could automaticaly convert it and users could select what unit they wanted a certain measurement in.
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Old Jun 19, 2002, 12:18 AM
Mitch G's Avatar
Naperville, IL USA
Joined Nov 2000
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I think predefined options for the inputs would help searches since the system designations would be consistent.
I would be concerned that an "other" option would deteriorate into a bunch of non-predefined options. Instead, I would like to see the user be able to send an email indicating when things aren't available in the list and then have them put in officially.
Obviously this makes extra work for the person maintaining the tool, but I think it will make the database all that more useful.


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Old Jun 19, 2002, 02:43 AM
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So....

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