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

[Istas]

macchesney: free lite + paid pro sounds like a good compromise; it would probably be used much more widely, and would let people see if the GPS units in their phone are accurate enough for it to be useful. (Incidentally, I would advise putting as prominently as possible somewhere obvious to see, "Test in clear skies and open areas for maximum precision; cloudiness and tall trees and buildings can ruin results."

In fact maybe you could make the pro version be "pay what you want" (with a minimum donation to eclipse the fees charged by payment methods); that way if someone's really appreciative they can show you.

If you're using local weather data, it'd probably be good to state how far away the station is; here in Montana at least it can be an hour's drive away, and change by 15 miles on a daily basis (depending on whether a personal weather station is actually functioning).

I believe correcting for gradient at highway speed would require having a fair idea of what the rolling resistance is (and that would also help get better precision on the cD calculation, obviously). You could have a low-speed rolling-resistance calculation too.

Other ideas: options to average multiple runs, as well as designate whether a run was heading east or west (or north-south, or headwind/tailwind, etc), and catagorizing saved runs under different settings (like snow tires, summer gas, cargo, different mods, etc).

...Reading up, I realize that's a lot of extra stuff. Don't mean to blather away, just throwing ideas out there.

[aerohead]

Originally Posted by 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!

The Society of Automotive Engineers SAE Handbook contains their protocol for coastdown testing.It is in fine print and runs to 2-1/2 pages of equations.All the procedures, parameters,instrumentation, and resolution of data are covered.
Statistically,in England,you'd have 7-days/year when it was calm enough for outdoor testing.This is why the Motor Industry Research Association created their wind tunnel.They just couldn't rely on the weather for meaningful testing.

[minispeed]

Originally Posted by 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!

Now that you mention it the one paid app that I have on my phone is a pro version that started out as lite so that marketing would probably work.

[Frank]

I don't know how quickly the GPS info updates but you'll want to pay attention to repeatability, etc. If someone runs the same vehicle the same way in the same place three different times and gets three different results that are nowhere close to each other you would probably see bad reviews pretty quickly. Good luck!

[NachtRitter]

Probably want a way to combine results from multiple runs as well