This one is for those of you with propeller hats or who are into tuning/measuring the performance of your cars, and it is only marginally Citroen related.
I recently stumbled across and tried a very interesting iPhone / iPod Touch app on my iPod Touch (no I can't afford an iPhone
)As some of you will probably know these devices have an accelerometer in them used to detect portrait / landscape orientation of the device for flipping the viewing mode etc.
What a lot of people don't know is that the accelerometer is a full 3 axis, 360 degree very high resolution solid state accelerometer which has incredible precision.
Hmm, so what could we do with an accelerometer and a car then ?
Enter the following app:http://dynolicious.com/index-2.html
I have to say I was a little bit sceptical at first even though I knew the accelerometer was very precise but I have been amazed by this app.
It basically has two modes, one is a "skidpad mode", the bottom left picture on the website, which is a real time display of maximum G-forces in the acceleration/braking axis as well as lateral G's for cornering, each one is measured in real time and the peaks are held. (until you reset it)
I can see that the (peak) acceleration figure would be great for getting quantitative results when tuning a turbo, or just comparing two otherwise identical cars where one seems to be down on performance.
Braking is another useful test - in fact a lot of smaller testing stations test the brakes on a car by doing a deceleration test with a portable accelerometer instead of putting it on a machine, so it's a valid way to evaluate braking.
Finally the lateral G-forces gives a good idea of the handling and grip of the tyres and suspension setup.
The second mode is a timed run mode which will do 1/4 mile run and then give you timings for all the standard (standard to the US imperial system anyway
) distances up to a 1/4 mile, and also 0-10mph 0-20 0-30 and so on, including 0-60, right up to whatever top speed you reached in the 1/4 mile.The cool thing about this mode is you don't have to press anything or look at anything while driving - while the car is stationary you press the start button, but it doesn't actually start timing until you accelerate, as it uses a 0.1G threshold to know when to start timing, and then beeps when it's finished collecting the results - no trying to punch a stop watch or look at a speedo while driving.
It does a nice little graph of the HP/G's/Mph vs time as well. All the results of the timed runs are saved under the profile for the car and you can create a separate profile for different cars.
If you tell it the weight of the car it also tries to estimate wheel horsepower - I say tries, because it cant account for wind drag, rolling resistance etc, although you could say that it is measuring "effective" horsepower when those are taken into account.
There's an interesting test of it's accuracy vs an actual test track with built in timing system here, if you can listen your way through the waffle to get to the important bits (fast forward is your friend, jump to about 2:30):
They didn't even have it mounted very well (they used a suction cup on the windscreen, so any movement will have reduced accuracy) and yet it was still surprisingly good.
How is it calibrated ? Easy - you use gravity itself as the 1G reference, the calibration involves holding the device up on each of its six axes in the calibration mode (I used a straight wall and a level bench top to do this) and takes just a few seconds.
It really does need a secure mounting though - when I tried it on my Xantia I found the iPod Touch is a perfect fit in front of the dashboard to the left of the speedo - a bit of blu tack at the top and bottom was all that was needed to hold it secure.
Now for the Citroen relevant bit, Mr Moderator
So how did the poor old Xant manage ? Being a slugomatic it didn't impress in the acceleration axis
and managed a pathetic 0.39G peak acceleration - and that was only in first gear. 0-60 time was a miserable 13.8 seconds when it should be about 11.4 seconds, so it isn't my imagination that it's performance is a bit on the flat side...(it's nice to have numbers now though)The braking was a bit more impressive though - despite me not being impressed with the sensitivity of the brake pedal compared to our other two Xantia's, in an ABS stop it manages 0.93G braking in the dry and 0.7G in the wet on 205/60/15 Michelin XM1.
I was also impressed by the lateral G's - in Hydractive sport mode it will also do 0.93G in sharp slow (around 25Mile/hr) corners without any tyre squeal. All the more impressive when I've read an Activa does 0.94G, although I'm sure the Activa would have rolled much less
I'd love to see what results an actual Activa would give.
Limitations: The horsepower figure is only an educated guess, no Km/hr mode, (a problem for me but not you guys
) it can only be accurate on level ground - as tilt of the car is interpreted as acceleration, naturally, although you wouldn't be doing timed runs on non-flat ground anyway.It needs a secure mounting in the car in the right orientation, you certainly can't hold it in your hand or lay it on a seat etc and expect any sort of accuracy.
You also can't save the graph of a timed run (only the result figures are saved) and there's no way to export the results to a computer, although you CAN take a screen shot of the display by holding the home button and pressing the sleep button, which will save the picture in the camera roll to be imported via itunes - yes, even on an iPod Touch.
Finally, it requires the iPhone/iPod Touch 2.0.x firmware to run.
Disclaimer: All testing was done on a "private" road with no other cars anywhere near, you should never do this sort of testing on a public road, and you should not be looking at a distraction on your dashboard while driving in an extreme manner.
I will not be held responsible for any accidents caused by using this program improperly. Enjoy.
Regards,
Simon
