G-Tech meter

[M HILL]

> Has anyone heard of an aftermarket measurement device called a G-tech me=
ter
> (at least that's what I think its called).  It's a small unit that stick=
s to
> your windscreen with a suction cup and plugs into the cigarette lighter
> socket for power.  It will give you g-forces, 1/4 mile time, HP rating a=
nd a
> few other things I think.  Someone in our car club bought one to try out=
 and
> he said it was quite accurate, the HP reading was 2HP less than actual
> measurements from dyno testing.  His 1/4 mile times were also close to
> actual times.
> 
> Has anyone used this device ?  I would like the feedback from a few more
> people before I'd consider buying one, although its reasonably cheap at
> AU$250 after freight and taxes.  I need something to help with setting u=
p
> the suspension in the race car, and this device may just be it.
> 
> How does it measure the distance (doppler effect ?), or does it calculat=
e
> distance from your acceleration ?  If this is the case how does it go in
> hilly areas, bumpy roads, etc ?
> 
> Thanks in advance
> 
> Dan     dzorde at geocities.com
> 
I sawthese advertised and thought that it would be simple to make up 
my own.  Sure enough within a week I had a fully built and working 
accelerometer.  The one that I built is programmable for the 
acceleration speeds, i.e. you could time 50 -70mph or 0-100 if you 
wanted.  It uses a 24 * 2 character LCD display and does maximum hold 
values for acceleration and braking as well as cornering force.  The 
distance calculation is done from the acceleration, the calculations 
are very simple to do.   The most expensive parts for it were the 
accelerometers which were u25 each but are good quality accurate 
ones.  There will be problems with going up and down hills and when 
you do not accelerate in a straight line.  The distance that the 
measurement is performed over is usually quite small so that errors 
that come about from the double integration required are quite small. 
 I am going to start some work on version two which will have more 
features such as storing the data at various points and automatic 
recalibration for accelerating round corners.  As for the 
performance.  I can't speak from experience of the G-Tech meter but 
mine is very good on consistency.  The timing is atarted 
automatically when an acceleration of more the 0.05G is detected so 
that false starts from vehicle vibrations are not a problem.  If you 
are interested in this and would like some help with the calculations 
I would be glad to help.  The work on the microcontroller was done on 
an 87C752 which is basically an 8052 core with built in EPROM and RAM 
and ADCs.  From what I've heard the G-Tech meters and accurate to 
within 0.4seconds and repeatable to within 0.2 seconds.  This is from 
some review in a magazine.

Martin