<all> home dyno kit??

[Roger Heflin]

On Thu, 28 Jan 1999, Mike Pitts wrote:

> >>This is because the 8192 sample time is maxed at about 8 frames/sec. 
> 
> Not if you know how to send the command to directly read ram 
> locations a single byte at a time, rather than asking for the entire 
> diagnostic stream. 8-)
> 
> If I can get 64 bytes out 8 times per second, I should be able to 
> get between 128 and 256 samples per second interrogating just 
> two bytes (RPM and MPH).  So sample rate is not a problem. 
> 
> The earlier post about poor resolution made a good point (25 RPM 
> and 1.0 MPH), you can however query the raw time between cam 
> sensor pulses and the raw VSS count and do your own math to get 
> as precise as you wish.  Or, at least I can do it with my PCM.
> 

I redid the program with interpolation.  THe results were better, but
there are still unexplained peaks (not TCC lock, or shifts).  I
believe the problem is that the acceleartions we are talking about are
1 mph/(1 or 2 or 3) frames, and some times it will be 1mph/2 and
sometimes it will be 1mph/3 (same sort of thing with 1 and 2) but 1/2
and 2/3 are the dV/dt components and vary too much because of the
limited dt.   If I am running an average accelearation rate of say 1.7
frames per mph, I get some where dV/Dt is 1 and some where it is 1/2
and this makes a big difference in hp numbers.

The program I have does attempt to take care of wind resistance via
a number for hp drag at 60.  It uses that equation of 

drag =   drag_at_60 *  ( velocity^2 / 60^2 ) which should give a
pretty good estimate.

Later this week I will try interpolating by fitting a equation to the
data in an attempt to get more accurate time data.   Also with the
reading of the mph and rpm at a higher rate, and interpolating the mph
data I think we could actually get good numbers.   2-3 times the
number of data points per second would probably give good enough data
(even with the 1mph resolution) to get good info.  The other choice
would be to read out the ABS computer as I understand it has very
accurate mph data.

				Roger