Computing MPH

[steve ravet]

You need Gs and time.  The first derivative of distance is velocity, and
the second is acceleration.  If you take the acceleration info,
numerically integrate w/ respect to time, you'll get velocity. 
Integrate one more time and you'll get distance.  It's easy to do:

Take each acceleration data point, multiply by the sampling interval. 
Sum these up to get your velocity.  If Gs are in ft/sec^2, you'll get
velocity in ft/sec.  There are other methods of mumerical integration
that are more accurate, you could find them in a starter calculus book. 
A faster sampling rate will improve the accuracy of this calculation but
it probably doesn't matter too much if you only want trap speed (vs
speed at other points on the track).

--steve

Steve.Flanagan at verizonwireless.com wrote:
> 
> I was at the track this weekend and pitted next to Victor Cagnazzi (#10 on
> the Pro-Stock Truck circuit).  Look for him in Indy this weekend, Great guy,
> gave us some clutch tuning tips and other.
> 
> He is using the RacePac data logger and it has a channel that shows MPH.
> This is not based off the Drive Shaft or other but it uses the G sensor.
> 
> I have a data logger that shows G's but does not compute MPH.
> 
> How would I go about figuring out MPH relative to G's?
> 
> I know how to compute relative to Drive Shaft.  This is not what I am
> asking.
> 
> What is the mathematics involved.  And does the Sampling rate of the G
> sensor make a difference or are we just concerned about the average G's and
> the time?
> 
> Thanks
> 
> Steve F

-- 
Steve Ravet
steve.ravet at arm.com
ARM,Inc.
www.arm.com
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