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Old 05-21-2014, 08:39 PM   #1 (permalink)
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[Android] Anyone Done a Coastdown App Yet? (to calculate CdA)

I know there's been talk of this, does anyone know if such a creature exists?

thanks,
Frank

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Old 05-21-2014, 10:39 PM   #2 (permalink)
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I have SpeedView, a speedometer app. It will record in one second intervals. I've opened a sample file in Excel. Next step is to do a coastdown and some math...
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Old 05-22-2014, 01:13 AM   #3 (permalink)
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Can you describe how you would expect it to work?
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Old 05-22-2014, 06:06 AM   #4 (permalink)
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I'm thinking start the app, accelerate to some predetermined speed (entered by user?) then coast in neutral. The device will use the GPS to record speed and calculate CdA.
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Old 05-22-2014, 10:08 AM   #5 (permalink)
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That would be neat. I wonder what the margin of error would be, and I imagine it would depend on the quality of the gps receiver in the phone.
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Old 05-22-2014, 07:24 PM   #6 (permalink)
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If you don't mind (or prefer) working in SI units, here is the process & equations given in my Bosch AUTOMOTIVE HANDBOOK, 1976, on page 223:

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Old 05-28-2014, 03:25 PM   #7 (permalink)
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Hi,

I just came across this post whilst searching the internet, and its great that there's recent interest in this as I'm working on one right now as part of a university project.

You input mass of car & frontal area and find a flat stretch of road, accelerate to any speed (100 km/h is fine), begin to coast, press 'start' on the app. Coast down for a while then press 'stop'. The app uses the GPS to log your distance vs time curve, and interprets this to calculate the drag coefficient Cd and rolling resistance Rd.

I'm mostly done programming but now need to validate/test!

Do you think there would be interest in this app? how much do you think is a fair price for such an app?
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Old 05-28-2014, 03:33 PM   #8 (permalink)
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Quote:
Originally Posted by macchesney View Post
Hi,

I just came across this post whilst searching the internet, and its great that there's recent interest in this as I'm working on one right now as part of a university project.

You input mass of car & frontal area and find a flat stretch of road, accelerate to any speed (100 km/h is fine), begin to coast, press 'start' on the app. Coast down for a while then press 'stop'. The app uses the GPS to log your distance vs time curve, and interprets this to calculate the drag coefficient Cd and rolling resistance Rd.

I'm mostly done programming but now need to validate/test!

Do you think there would be interest in this app? how much do you think is a fair price for such an app?
Sounds good, I think there would be interest but as for a fair price I think you'd want to make money selling ad space. I'm pretty used to getting free apps that do most things and putting up with the ad's. I may pay 99 cents for it if it got good feedback from others.
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Old 05-28-2014, 03:38 PM   #9 (permalink)
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macchesney: It would be useful to include altitude change as well, so people can tell if they're sorely mistaken about just how level a particular road is.
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Old 05-28-2014, 03:50 PM   #10 (permalink)
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Thanks for the replies guy,

Minispeed:
I agree with you, in order to get this out to as many people as possible it would be better if it were free. Perhaps i'll make a lite & a pro version, with additional features in the pro version such as the ones mentioned below!

That's a great idea Istas, i'll be sure to implement this. It currently uses your location to calculate ambient conditions such as air density and wind and I've been meddling with the idea of correcting for gradient of the road too - though this is quite complex and I dont know how to do it at the moment!

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