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Old 04-20-2011, 03:10 PM   #41 (permalink)
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Quote:
Originally Posted by bobski View Post
Why even bother with the Cd calculations then?
Because it makes it convenient and accurate, why do you think?!? Having a relative number is very useful for determining if a mod was useful.

Really the thing limiting its accuracy is getting the vehicle weight correct (and there is already a configuration parameter for that). And you can always correct for current conditions later.

But you need to do something like a 55-50mph coast and a 7-3mph coast to deternine CDA and Rolling Resistance.

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Old 04-20-2011, 03:36 PM   #42 (permalink)
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But folks are more interested in completely rewriting things (sometimes blindly)... It aint broken. Heck, it has an event scheduler.
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Old 04-20-2011, 11:37 PM   #43 (permalink)
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Quote:
Originally Posted by dcb View Post
But folks are more interested in completely rewriting things (sometimes blindly)... It aint broken. Heck, it has an event scheduler.
I'm no programmer, but i believe Falcon4 just felt that cleaning up the code would make it easier for future open source coding, adding of new features, making the UI more refined and easier for regular folk. Also making software updates easier for regular folks as well.

He and all of us praise your efforts and amazing gauge as it has made our ecomodding efforts easier and more quantifiable.

If Falcon4's software changes don't make the gauge work better/easier/more efficient, then you are right, if it wasn't broken why fix it, and then people won't update to Falcon4s new software on your Opengauge. But he has already showed that his mods, clock, miles to empty tank, tank figures, easier configure menu, and duck mod are all very useful. Well except the Duck!

I think his efforts will prove to be useful and since this was started as an opengauge, open software, open architecture project, he is openly trying to better said project.
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Old 04-20-2011, 11:40 PM   #44 (permalink)
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Oh, and as for the coefficient of drag thing. Definatley having the mpguino calculate this would be cool, but you would have to run several tests on the same stretch of road, and the longer the mph coast-down the better. It would give a larger sampling of data. Instead of it took 1 second to coast from 55-50, it took 9.26849 seconds to coast from 55-10. Given the same road stretch with same gradient, same weight, same tire pressure, ect. ect. ect. Gotta try to make it the closest apples to apples within reason.
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Old 04-21-2011, 12:30 AM   #45 (permalink)
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It can't be that big of a range since force slowing the car down changes from majority aerodynamic for 55+mph to majority rolling resistance below 25mph. You want to measure aero drag when it is the highest force(rolling resistance negligible) changing the velocity of the car, so maybe 65 to 50 or something, then subtract the rolling resistance using a coast down from 20 to 5 or something where areo is negligible.
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Old 04-21-2011, 12:59 AM   #46 (permalink)
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Yah, that is basically the idea.

You would use like a 5-3mph reading as the basis for computing rolling resistance, then use the 55-50 to compute CDA (which the program would subtract out rolling resistance). Yes more runs, in both directions would help, especially if it is easy to use. And if you enter the displayed CDA and RR numbers into a web page with your zip code shortly after the tests, it can look up your current temperature and pressure for you and print out "corrected" CDA and RR figures
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Old 04-21-2011, 01:25 AM   #47 (permalink)
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I think it would be best to stick with a simple coast down timing aid rather then pretending to calculate an accurate CD. A simple timing aid would improve coast down timing over a stop watch and could be every bit as useful for comparing aero mods as an estimate of CD.

Unless the instrument logs wether data you need to keep track of that separately. Enter the weather data and coast down info in a spread sheet and do the data reduction where you can work comfortably.

To compare data from different days requires correcting for air density. Of course you would always use the same road with multiple runs in each direction and average. If your looking at fine tuning you get excited about drag changes of 1%. Trying to measure that amongst the affect of things like light breezes, changes in air density, and lubricant viscosity changes with temperature requires carefully correcting for known variations to pull something very small out of a whole lot of noise and variations.

With an aero mod that is easy to install/remove you can do ABA testing in one session so you would not need to make any corrections to timing data to evaluate a drag change.

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Old 04-21-2011, 01:41 AM   #48 (permalink)
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Also, I want to clarify, I don't have a problem with FFs mods, he appears to have taken some time to understand the current source (sort of necessary for an open source project to succeed). I just think it needs a unique working name for now so I am not left holding the bag. But I have seen a number of would-be contributors decide that completely rewriting it to their own ideology was "helpful", and rarely did it come with any serious testing or modder oriented features. Don't get me wrong, they mean well and are excited to show off their stuff, but they don't always come at it with an experienced modder perspective and thus the offerings are high effort-low value IMHO.

I did want to emphasize that it is the modders here that motivate me more than anything. It is the folks that do diligence in experimenting and documenting and testing rigor and sharing their methods and results that get the best value for everyone else (and even dare I say influence industry occasionaly). Given this is still a limited resource platform I think the priority features should target modders as a result and enable them to test their mods, be it grill blocks or warm air intakes or ?!?

Arduino is a great learning environment. I would encourage anyone getting started to experiment with it BUT:

I would also reiterate that arduino is only good for prototyping on a project like this, from my experience. And the mpguino is well beyond the prototype stage. For $10 you can get a real programmer Make Your Own MP3 Player that allows you to set more stable fuses, reclaim 2k of bootloader space, faster startups, ability to program eprom directly, and no depenancies on arduino. Additionally the arduino software is still in flux, so stuff breaks as everyone has different versions. Plus this code is faster than the arduino equivalent. Finally it removes a layer of "non accountability" if you do not depend on arduino and another layer of code bloat libraries. Arduino and bootloaders are not a good choice for a production environment, I have learned this once already, believe me. GCC isn't that bad. Eventually I am going to use a timer or some other resource that arduino thought they had complete dominion over and it will no longer be compatible at all (and isn't compatible with some versions already).
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Old 04-21-2011, 01:57 AM   #49 (permalink)
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Quote:
Originally Posted by msc View Post
I think it would be best to stick with a simple coast down timing aid rather then pretending
Pretending? If you go to the truck stop and weigh your car, wait for a calm day to do your tests, and the program helps get current air density data off the web for your test site to come up with reasonable figures, how is that pretending? Most obd gauges come within 3%, would you say they are "pretending too"? The point I'm trying to drive home is to make it easy for modders, the inspiration for this project, and to use the remaining resources to target that audience, not joe mashpedal.

Spreadsheets? You don't need any instrumentation changes at all if that is your argument, just write real fast

Obviously there needs to be some compromise between cost, installation difficulty, accuracy, ease of use. I think there is a reasonable approach that doesn't require pitot tubes to get a very good estimate of CDA, but it has to leverage online weather data for costs/simplicities sake. There may even be historical data by zipcode where you just need to enter the date/time/zip and the displayed CDA/RR numbers from your log.

Of course if you have pressure and temperature and humidity and wind instrumentation handy, then log those absolutely. Obviously teach the online program to allow you to override the web based weather with on-site measurements. I'm sure such instrumentation will be necessary to compare with the web derived weather results before stating that anyone is "pretending".
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Old 04-21-2011, 02:16 AM   #50 (permalink)
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here are some online weather APIs that might work in a CDA mashup.
5 Weather APIs – From WeatherBug to Weather Channel

Of course you can do your own testing without standardizing the results and by choosing your test times even more carefully (look at the hydrometer,barometer,temperature).

And there would be some standardized warm up routine in any event, this is business as usual for any testing.

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