Squizz

Well, my friend set it up - But he ensured it was on 0.00g before setting the GO mode.

I suppose it shows the value of 4WD versus FWD, in the case of my scoob versus some hot hatches.

Having said that, I know for a fact that my friends car (modified Punto turbo) is near as dammit quick as my scoob when rolling and above second gear. Unless it's wet, when his car will spin the wheels in virtually any gear!! Mind you, above 100mph (on a private road) his car might as well be in reverse

brickboy

Squizz, GEJL, how do they work, and how does the unit know when you've hit 60 ... or do you shut it off manually? Any idea how much, too?

Good times, by the way ;-)

mega_stream

I had a look at these from the banner ad link on here other week..so these things just sit in the car, no wires, and can tell
a) how fast your going?
b) record 1/4 mile times?

how? Me no understand

I'm sure the work and work very well, I just can't understand how they do it?

Squizz

Last night, a friend of mine came round with one of those G-Meter thingies, that are supposed to be accurate to 1/10 second.

So... MY99, K&N57i induction kit, SS Backbox, Driver & Passenger, 1/3 tank of petrol (Optimax), and some stuff in the boot.

Apparently managed:

0-60 in 5.38 seconds.

1/4 mile in 14.02 seconds @ 101.1mph

My friend was amazed, as they'd only ever used it in hot hatches before now, and got believable times in the 7-9 second bracket. I didn't exactly punish the car doing the time either. There's plenty that could have been done to improve the time.

Are these things accurate, or not?

Edited to say:
On a nice piece of tarmac on a friends private estate, Officer...

[This message has been edited by Squizz (edited 18 September 2001).]

GEJL

I've got one of those (a GTech Pro), and figured my bog-standard MY00 turbo at just under 6s (5.8 or something, can't remember exactly). I think they are a bit on the optimistic side, but probably not hugely. They are affected by road gradient, the tilt of the car on its spring under acceleration etc, and also whether it was dead on 0.00g when you hit the button to set it up.

My Elise also came in at around 5.8s too, which is probably less affected by body tilt.

Most of use for comparisons between mods on the same car, rather than comparisons with other measurement methods, I reckon. At the moment I'm working on getting some figures to compare running my car on standard 95 RON UL and then switching to the Optimax stuff, using the BHP measurement function. I'll post details when I've got them!

The bit of kit which is possibly more accurate than the GTech is the AP-22, which allows you to set all sorts of extra parameters such as drag, tilt etc. I've not tried that yet, though.

Only over used on an airfield, of course.

Squizz

I'm not sure how they measure when they've reached 60 or 1/4 mile...

I know they use a potentiometer to measure G-Force/Acceleration, but I don't know how they measure distance covered. Certainly not via Datron style lights, or via GPS.

Squizz

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by brickboy:
<B>Squizz, GEJL, how do they work, and how does the unit know when you've hit 60 ... or do you shut it off manually? Any idea how much, too?

Good times, by the way ;-)[/quote]

Stick the little unit onto the windscreen via a sucker, and plug it into the cigarette lighter to power it.

Find a level stretch of tarmac, and adjust the meter for tilt until it reads 0.00 (perfectly level).

Press a button to activate, and the display says "GO". You can then start in your own time. As soon as the unit measures acceleration it begins to measure the runs.

Once 1/4 mile has been achieved, it stops measuring, and displays the times.

There is another mode where you can input vehicle kerb weight, and having done the run it'll give a reading for calculated BHP at the wheels. (Yeah, right! )

carl

This is basic applied maths. You know the initial velocity (u) which is zero. The device can measure acceleration (a) and time (t). What you want to know are displacement from start position (s) and final velocity (v).

Standing quarter is given by:

s=ut+(1/2)at^2 -- record t when s gets to 1/4 mile

0-60 is given by:
v=u+at -- record t when v gets to 60 mph.

It's just an exercise in integration -- acceleration is rate of change of velocity, and velocity is rate of change of displacement.

Converseley, GPS speed/acceleration measurement is the other way round and is an exercise in differentiation.

AndrewC

If you start from stationary then velocity and distance are functions of acceleration and time.

Can the gizmo measure in-gear acceleration? for me 30-70, 50-80 etc are more important than off-the-line measurements.

Andrew...

[edited to say I was too slow and over simplified in my answer ]

[This message has been edited by AndrewC (edited 18 September 2001).]

GEJL

Minor correction to Squizz in that they use an accelerometer to measure the instantaneous acceleration. The GTech has a single one to measure acceleration in one direction only (i.e. acceleration/deceleration if it's mounted on the windscreen facing you, though you can do cornering (lateral) 'g' if you stick it on a side window). The AP-22 has two, I think, and can mesure both longtitudinal and lateral g at the same time (it also can download readings to a PC - nice...)

I think the AP-22 can do in-gear times as well, but the GTech can't.

The GTech is around £120 (IIRC) ordered direct from the US (www.gtechpro.com), the AP-22 is around £160ish+VAT. I would have got the AP-22 except I didn't find out about it until after I got the GTech... There's also a cheaper version of the AP-22 that doesn't have the data download facility.

There've been a few group buys on the AP-22, on the pistonheads board, I think. (www.pistonheads.com/gassing). Maybe also on this board?

Squizz

And I thought Java Developers were scary...

The real answer will be found if I do a proper run at a RWYB, then.

brickboy

Thanks to all for the input ... but how does it know when you've hit 60 / reached the end of 440 yards? Surely you have to hit a button or something?

Squizz

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by brickboy:
<B>Thanks to all for the input ... but how does it know when you've hit 60 / reached the end of 440 yards? Surely you have to hit a button or something?[/quote]

To Paraphrase Carl & Plagarise AndrewC

"If you start from stationary then velocity and distance are functions of acceleration and time."

It just basically figures out the distance travelled by the acceleration factor and the time taken so far.

Or summat like that!

AndyMc

As the others have said if you measure the acceleration(which is the push in the back you feel when you floor it) and also measure the time you have been accelerating for you can work out the speed you will be going and the distance you have covered.

You don't actually have to do make any connections to the speedo or press any buttons, sounds weird I know but its just simple maths

For example if it was to measure 1 G (as in the acceleration due to gravity) for say 4.5 seconds it would calculate that you are doing exactly 100 mph.(there are'nt many cars that can do that)

My mate sets up instruments on fighter aircraft which work in exactly the same way but measure in all three planes(pun intended)
Ie up/down,side/side and forward and back.
These are so accurate that the pilots takes off and flys around for half an hour,the instruments measures the forces and work out the speed and distance and height.When the plane lands again the computer gives a position thats only a couple of feet away from where the plane actually is which is pretty awesome.

The problem with the car ones is that the accelerometers are not as accurate and they normally only measure in one plane so they need to be perfectly level.This doesn't mean you won't get accurate results though .

Andy

mega_stream

Anyone know the url of the place that sells these?

I saw it on an ad banner on here the other week, can't see it know..

Maybe it would be a good idea to have a "traders" area for direct links to paying advertisers sites?

GEJL

AP-22 is available here (don't know if this is the manufacturer or a third party):

teknopete

Hey peebs,

My input 4WIW, have both an AP22 and blitz MFTT in my scoob The MFTT is hardwired, the AP22 is not. Yet the figures from both are very similar 4 the 1/4 so I`d say they must be pretty dam good no?
As GEJL said the AP22 has 2 accelerometers and can measure G-circle, cornering G force an a bunch of other stuff as well as straight line acceleration. One thing 2 bearin mind though is if the figures u use when setting them up are pants then the resulting figures will be rubbish. (hell i had my car weighed 2 make sure the figures were right Comparing a downloaded run with a dyno run the figures r very close.

Pete