[Android] Anyone Done a Coastdown App Yet? (to calculate CdA)

[Frank]

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

thanks,
Frank

[ennored]

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...

[NachtRitter]

Can you describe how you would expect it to work?

[Frank]

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.

[Istas]

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.

[gone-ot]

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:

[macchesney]

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?

[minispeed]

Originally Posted by macchesney

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.

[Istas]

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.

[macchesney]

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!