Build your own 5th wheel update

[Daniel R Burk]

Well, I have my 5th wheel working on my bench at the lab.  Here's the system
as it stands:

        I will be collecting six channels of data at the dragstrip:
        1) ADXL105 1 axis accelerometer
        2) Engine RPM
        3) 5th wheel pulse count (distance)
        4) 5th wheel frequency count (speed)
        5) Air temperature at the air cleaner
        6) Barometric air pressure

I hope to correlate the 5th wheel data with the accelerometer data by
integrating the accel data.  I'm collecting 20 samples per second, and I trigger
the data collection whenever the accel exceeds 0.25G's.   I take a 30 second
snapshot, and viola!  one dragstrip run captured and digitized.   I'll be
post processing the data using Excel, but I might try MATLAB later on.

The 5th wheel consists of a 26 inch bicycle rim mounted on a cast-off
mountain bike fork.  The wheel has been modified with aluminum tape with a
5/16 inch cut-out every ten degrees.  I shine a high intensity infrared LED
through the hole directly at a shrouded phototransistor.  The
phototransistor is forced into saturation by the LED causing a voltage drop.
I have a .01uf capacitor in series to my signal line and this prevents
problems caused by DC offset from ambient infrared.  (I think... Hey, it
works so I left it in !) )

I am now making the bracketry to mount the 5th wheel to the back of my car.
It gets tested the morning of the 27th at Milan Dragway in Milan, MI  so
I'll let you know if the 5th wheel can read speeds greater than the 15MPH
that I've read in the lab.  I'm shooting for 91 MPH with the Trans Am.

        -- Dan.