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Old 11-24-2005, 02:33 PM   #1
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What I Drive: 2005 ZX3 5spd

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NOT SPAM: $37 stick-on 1/4mile 0-60mph time meter

Do you have an access to a level 1/3 to 1/2 mile strip of flat pavement you can go back 'n forth and stop anytime? If not, move on...

Well, I bought an interesting toy and the price was really good so I thought I'd share my experience with you guys. I'm not affiliated with them in anyway, so I really don't care whether you buy one or not.

I bought an accelerometer based performance gauge. It mounts on the windshield and it looks exactly like a radar detector. GTech and Vector FX makes these and the new model is around $150. The one I have is their first release model released in 1994, but I can't complain much for $37.

I bought it on eBay from this store

The new model is a lot more user friendly, have tons more features and doesn't need to be leveled. They have 3-axis accelerometer so it automatically compensates for tilt by subtracting the vector.

My basic model can measure:
Instantaneous G force anytime

It can only measure the below only if you start from dead stop and take off aggressively.
0-60, 60-0 time
1/4 mile time
peak horsepower (you have to program in the exact weight of you + the car, you need to make sure the engine redlines in first gear)

For those of you who cares to know how it works:

The fuction d(t) represents position with respect to time, its first derivative d'(t) is the velocity and the second derivative d''(t) is the acceleration. t= time.

The accelerometer can directly measure the acceleration experienced. By attaching it to the car, it is identical to what is seen by the car.

When you take the integral(anti-derivative) within defined limits of integration, it is possible to find the exact value of lower derivatives. When you set Gtech to "ready" and launch with enough jerk ( third derivative) , it sets the lower limit of integration as 0, starts the stopwatch and starts to integrate continuously.

In 0-60 mode, when d'(t) reaches 60mph, it reports the the upper limit of integration, which is the time counted by the stop watch.

In 1/4 mile mode, when d(t) reaches 1/4 mile, it reports the time, and d'(t) which is the instantaneous velocity when d(t) was exactly 1/4 mile.

If you tell the computer the weight of your car + you, it can also calculate out peak horsepower.

Unfortunately, with each level of integration, error accumulates. If one could tap into the ABS sensor signal, you'd have direct access to d(t) function and you can get the 1/4 mile time directly and trap speed by taking the first derivative.

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