[time-nuts] A real world project need for timing accuracy...
Predrag Dukic
stijena at tapko.de
Tue Nov 2 02:04:34 UTC 2010
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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