[time-nuts] A real world project need for timing accuracy...

[Predrag Dukic]

Why not using optical methods for shot grouping?

A cheap web camera with equally cheap telescopic lense can resolve 1mm.
Some image processing software can find shot positions within the 
1kx1k pixel bitmap.... etc..




At 01:03 2.11.2010, you wrote:
>    Timenutters--
>    I appreciate the feedback for implementing my
>    ballistic field measurement project but I think
>    there is some misunderstanding of what the goal is.
>    For instance, it is not practical to find 800 meters
>    of coax and trench it in out to the downrange target.
>    This system needs to be relatively portable so it
>    can be set up at any given shooting range.
>    I need to determine: A) down-range velocity of the
>    still super-sonic projectile, B) time of flight and
>    C) shot-group size.
>    Measuring down-range shot-group size with an array of
>    ultrasonic sensors is pretty straightforward. I can
>    do all the computation with a $6 microprocessor and
>    send the X/Y coordinates back to the laptop at the
>    shooting bench with a simple RF link.  Down-range
>    velocity is easily determined with a set of sky-screens
>    and the results also sent back via an RF link.
>    Time-of-flight is much more problematic to determine
>    but the plan is to determine the elapsed time between
>    the moment the projectile passes over the muzzle skyscreen
>    and the moment of passing over the downrange skyscreen.
>    This means syncing the 10 MHz clocks at both ends together.
>    I guess the crux of my question to the time-nuts gang
>    is what is the easiest (cheapest!!) way to do this.
>    For a number of years I have been using an ultrasonic
>    shot-group size measurement system made by Oehler
>    Research.  It can resolve individual shot placement
>    to within 1 cm.  Some less expensive systems that
>    use fewer sensors can only resolve to +/- 2 cm. The
>    Oehler Research system also determines time of flight.
>    The problem is that these systems all use a cable
>    to connect back to the equipment at the shooting bench.
>    I am trying to find a way to synchronize/coordinate
>    a downrange 10 MHz clock to the "master" 10 MHz system
>    clock at the shooting bench without spending hundreds
>    of $$ doing it.  It is not too big a problem to process
>    all of the signals from the downrange skyscreens and the
>    ultrasonic shot-group sensors and telemeter the results
>    back to the shooting bench.
>    However, time-of-flight info (via an RF link requires
>    that I sync the 10MHz clocks at both ends together.
>    Use of GPS receivers seems to be the most likely way
>    to do this but how do I keep the cost and complexity
>    down?
>    Thanks in advance for any feedback on the matter!
>    Mike Baker
>    ---------------------
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