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

[Richard W. Solomon]

Don't try telling that to the Gunny at Sniper School !!

73, Dick, W1KSZ


-----Original Message-----
>From: Bob Camp <lists at rtty.us>
>Sent: Nov 1, 2010 7:08 PM
>To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
>Subject: Re: [time-nuts] A real world project need for timing  accuracy...
>
>Hi
>
>Two gotchas, one minor, the other a bit bigger.
>
>At 800 yards, even a *very* good optical setup can't / won't see holes in a target. The atmosphere is just to unstable. You would have to mount the camera down range (minor issue).
>
>The larger one is that you really don't want to truck down a half mile of path to put up a new piece of paper. After a while the "target" gets pretty ragged. There's not much for the optics to pick up, especially if you have good groups. 
>
>Cool idea though ....
>
>Bob
>
> 
>On Nov 1, 2010, at 10:04 PM, Predrag Dukic wrote:
>
>> 
>> 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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>> 
>> 
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