A real-world precision timing need....
Hello, Time-Nutters--
A real-world precision timing need:
As a dedicated long-range rifle shooter and
ballistics enthusiast, I am in the early stages
of a project I am getting started on...
The object is to measure the velocity of a
rifle bullet both at the muzzle and downrange at
various distances up to 800 yards/meters or so.
Conventional optical sky-screens will will be
used for measuring the velocity at both ends.
However, I also need time-of-flight and this
requires knowing the timing relationship between
the time the bullet crosses the muzzle sky-screen
and the downrange sky-screen. Bullet muzzle velocities
will be between 1900 to 3200 feet-per-second.
Additionally, I will be using the output from an
array of 4 ultrasonic sensors located on the
corners of a 4-foot PVC pipe square to determine
the size of the shot group at the far end and
telemeter this info back to a laptop at the
shooting bench.
I can use a 10-MHz crystal for the sky-screen clocks
and the for the 4 ultrasonic bullet shot location
sensors. However, determining the time-of-flight is
a more difficult task as this requires syncing clocks
together at both ends to a moderate degree of accuracy.
Out to 100 yards I can send the time-of-flight
far-end pulse back by wire and compare it to the
muzzle-end sky-screen pulse but this is not practical
to do by wire out at 800 yards.
This project is on a tight budget-- namely, MY
wallet, so cost is a major concern. Suggestions
will be most welcome!!
Thanks!!
Mike Baker
Gainesville, Florida, USA
Hello,
Long ago I was involved in a project that has something to do with test
cannons. They used a doppler radar (a commercially available equipment,
but I don't remember the manufacturer) for measuring the speed of the
bullet (a rather big one... if I was right, it was a 155mm caliper :) )
during its travel from the cannon aperture to the end point (about 500m
distance or so).
Regards,
Javier
El 31/10/2010 13:56, Michael Baker escribió:
Hello, Time-Nutters--
A real-world precision timing need:
As a dedicated long-range rifle shooter and
ballistics enthusiast, I am in the early stages
of a project I am getting started on...
The object is to measure the velocity of a
rifle bullet both at the muzzle and downrange at
various distances up to 800 yards/meters or so.
Conventional optical sky-screens will will be
used for measuring the velocity at both ends.
However, I also need time-of-flight and this
requires knowing the timing relationship between
the time the bullet crosses the muzzle sky-screen
and the downrange sky-screen. Bullet muzzle velocities
will be between 1900 to 3200 feet-per-second.
Additionally, I will be using the output from an
array of 4 ultrasonic sensors located on the
corners of a 4-foot PVC pipe square to determine
the size of the shot group at the far end and
telemeter this info back to a laptop at the
shooting bench.
I can use a 10-MHz crystal for the sky-screen clocks
and the for the 4 ultrasonic bullet shot location
sensors. However, determining the time-of-flight is
a more difficult task as this requires syncing clocks
together at both ends to a moderate degree of accuracy.
Out to 100 yards I can send the time-of-flight
far-end pulse back by wire and compare it to the
muzzle-end sky-screen pulse but this is not practical
to do by wire out at 800 yards.
This project is on a tight budget-- namely, MY
wallet, so cost is a major concern. Suggestions
will be most welcome!!
Thanks!!
Mike Baker
Gainesville, Florida, USA
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While in the shower:
You have the advantage that most of the
equipment will be more or less in line,
and you will have line of sight.
What if, at each station, you let your
microcontroller generate a 10kHz carrier
modulated by a 5kHz PN code, through an IR
led, and through a plastic lens (children's toy
magnifier? cheap plastic reading glasses?),
pointed back at the shooting stand. Invert at
50bps, and you have your data backhaul.
At the receiver end you have an IR receiver,
go into a sound card, and in software recover
the code from each of the all simultaneously
transmitting stations. In the process you
get the clock offsets of each of your stations.
Subtract this out before post processing.
25 usec should be achievable,
25us*3200f/s=0.08f
Very similar to something called 'GPS'.
Only using NIR light.
/Kasper Pedersen
On 10/31/2010 01:56 PM, Michael Baker wrote:
Hello, Time-Nutters--
A real-world precision timing need:
As a dedicated long-range rifle shooter and
ballistics enthusiast, I am in the early stages
of a project I am getting started on...
The object is to measure the velocity of a
rifle bullet both at the muzzle and downrange at
various distances up to 800 yards/meters or so.
Conventional optical sky-screens will will be
used for measuring the velocity at both ends.
However, I also need time-of-flight and this
requires knowing the timing relationship between
the time the bullet crosses the muzzle sky-screen
and the downrange sky-screen. Bullet muzzle velocities
will be between 1900 to 3200 feet-per-second.
Additionally, I will be using the output from an
array of 4 ultrasonic sensors located on the
corners of a 4-foot PVC pipe square to determine
the size of the shot group at the far end and
telemeter this info back to a laptop at the
shooting bench.
I can use a 10-MHz crystal for the sky-screen clocks
and the for the 4 ultrasonic bullet shot location
sensors. However, determining the time-of-flight is
a more difficult task as this requires syncing clocks
together at both ends to a moderate degree of accuracy.
Out to 100 yards I can send the time-of-flight
far-end pulse back by wire and compare it to the
muzzle-end sky-screen pulse but this is not practical
to do by wire out at 800 yards.
This project is on a tight budget-- namely, MY
wallet, so cost is a major concern. Suggestions
will be most welcome!!
Thanks!!
Mike Baker
Gainesville, Florida, USA
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I'd think you don't even need the pn code. Check out any of the wireless modules for sending analog video on 2.4ghz.. Cobble together an antenna with gain.
Calibrate the delay throughout the hardware at 50 yd or so using hardline compare, and extrapolate to longer ranges.
On Oct 31, 2010, at 6:40 AM, Kasper Pedersen time-nuts@kasperkp.dk wrote:
While in the shower:
You have the advantage that most of the
equipment will be more or less in line,
and you will have line of sight.
What if, at each station, you let your
microcontroller generate a 10kHz carrier
modulated by a 5kHz PN code, through an IR
led, and through a plastic lens (children's toy
magnifier? cheap plastic reading glasses?),
pointed back at the shooting stand. Invert at
50bps, and you have your data backhaul.
At the receiver end you have an IR receiver,
go into a sound card, and in software recover
the code from each of the all simultaneously
transmitting stations. In the process you
get the clock offsets of each of your stations.
Subtract this out before post processing.
25 usec should be achievable,
25us*3200f/s=0.08f
Very similar to something called 'GPS'.
Only using NIR light.
/Kasper Pedersen
On 10/31/2010 01:56 PM, Michael Baker wrote:
Hello, Time-Nutters--
A real-world precision timing need:
As a dedicated long-range rifle shooter and
ballistics enthusiast, I am in the early stages
of a project I am getting started on...
The object is to measure the velocity of a
rifle bullet both at the muzzle and downrange at
various distances up to 800 yards/meters or so.
Conventional optical sky-screens will will be
used for measuring the velocity at both ends.
However, I also need time-of-flight and this
requires knowing the timing relationship between
the time the bullet crosses the muzzle sky-screen
and the downrange sky-screen. Bullet muzzle velocities
will be between 1900 to 3200 feet-per-second.
Additionally, I will be using the output from an
array of 4 ultrasonic sensors located on the
corners of a 4-foot PVC pipe square to determine
the size of the shot group at the far end and
telemeter this info back to a laptop at the
shooting bench.
I can use a 10-MHz crystal for the sky-screen clocks
and the for the 4 ultrasonic bullet shot location
sensors. However, determining the time-of-flight is
a more difficult task as this requires syncing clocks
together at both ends to a moderate degree of accuracy.
Out to 100 yards I can send the time-of-flight
far-end pulse back by wire and compare it to the
muzzle-end sky-screen pulse but this is not practical
to do by wire out at 800 yards.
This project is on a tight budget-- namely, MY
wallet, so cost is a major concern. Suggestions
will be most welcome!!
Thanks!!
Mike Baker
Gainesville, Florida, USA
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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On 10/31/2010 01:56 PM, Michael Baker wrote:
Hello, Time-Nutters--
A real-world precision timing need:
As a dedicated long-range rifle shooter and
ballistics enthusiast, I am in the early stages
of a project I am getting started on...
The object is to measure the velocity of a
rifle bullet both at the muzzle and downrange at
various distances up to 800 yards/meters or so.
Conventional optical sky-screens will will be
used for measuring the velocity at both ends.
However, I also need time-of-flight and this
requires knowing the timing relationship between
the time the bullet crosses the muzzle sky-screen
and the downrange sky-screen. Bullet muzzle velocities
will be between 1900 to 3200 feet-per-second.
Additionally, I will be using the output from an
array of 4 ultrasonic sensors located on the
corners of a 4-foot PVC pipe square to determine
the size of the shot group at the far end and
telemeter this info back to a laptop at the
shooting bench.
I can use a 10-MHz crystal for the sky-screen clocks
and the for the 4 ultrasonic bullet shot location
sensors. However, determining the time-of-flight is
a more difficult task as this requires syncing clocks
together at both ends to a moderate degree of accuracy.
Out to 100 yards I can send the time-of-flight
far-end pulse back by wire and compare it to the
muzzle-end sky-screen pulse but this is not practical
to do by wire out at 800 yards.
This project is on a tight budget-- namely, MY
wallet, so cost is a major concern. Suggestions
will be most welcome!!
I can see two basic approaches to this...
In one you let your communication link do time-transfer between your gun
and target, and in the other you have relieved it from this requirement
and just use it to transport measurement results.
I assume you already have ideas for muzzle speed measurements, but it
can be treated as a fairly separate problem.
Considering that your time of flight is in 750-1300 ms range, providing
1 ms accuracy on time of flight would get you a fair precision here.
Let's assume that we only consider the timing errors right now.
One approach would be to use a pair of GPS receivers. Use the muzzle/hit
detection as start and measure the time to the GPS PPS signal. Using a
standard 1 MHz garden varity oscillator (DIP14 +/- 100 ppm) would give
you 1 us resolution and 100 us worst-case scale error due to scale error
from frequency error and 1 us from GPS (from the data-sheet numbers).
Not too bad. You just time-stamp with the NMEA string and extend with
the measured PPS difference (1 s - measured value). You could probably
make a PIC/AVR do the necessary processing and then use whatever
back-haul you like to relay the signal back.
If you find yourself a couple of Jupiter GPS receivers, they have a 10
kHz output which is locked to the GPS, so that way you get comparable
performance but without an oscillator. If you need additional
performance you can use a 10 MHz oscillator to interpolate to the 10 kHz
wave... but now with much less scale error.
Another approach would be to have two OCXOs and let one of them "lock
up" to the other. Either by having the target OCXO lock over the link to
the gun side, or you have them sit next to each other, heat them up and
have the target variant learn time and frequency of the gun one. Once
locked up the frequency is held by a DAC, their time-scales run of each
clock and it is used for time-stamping just as above. This would also be
on the level of a little PIC/AVR programming. Should give you sufficient
precision while not being to expensive. You won't need GPSes here, so
there is two GPS receivers and antennas of the budget.
Finding a suitable data-link is much more an issue than the time-scale
and time-stamping issues, which could be done with sufficient precision
for not too much money and effort.
Cheers,
Magnus
XBEE PRO XSC + PIC can do datalink this for about 75$ / observation point,
if you don't require high throughput
Xtof.
Finding a suitable data-link is much more an issue than the time-scale
and time-stamping issues, which could be done with sufficient
precision for not too much money and effort.
Cheers,
Magnus
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Hi
Been down this road before.
The issue turns out to be the optics in the sky screens. You can only get "just so good" without fancy optics. The normal photo detector behind a slit with the sky as the light source is far from optimum. If you are going to put money into the system, the optics are where it should go. Optical detection down range (over a large region) is tough. The simple sky illuminated optics you normally see are only "good" out to about 12" from the detector, past that they begin to degrade. Also remember that if you drop sub-sonic at 800 yards the shock wave will arrive before the bullet. That can mess up things as well.
By far the cheapest solution is going to be a 800' spool of mil surplus telephone wire. You may have to hunt a bit, but the stuff is out there dirt cheap. Run the screens normal (in close spaced pairs). Interface the wire to the serial output of what ever the sky screens are hooked to. Put on any of the normal line extenders to run down the cable. The baud rates are low enough that it should work quite well. If you run the sky screens in pairs the whole time base problem goes away.
If you want to run the screens in wide spaced pairs, boost the output with an amp that matches the wire you have. That will give you time of flight, but not actual velocity.
Another nice thing about wire - if you have AC power at the bench, you can feed the down range stuff from it. No honking big car batteries to haul down range and forget to charge.
Cost wise - anything that's exposed down range is likely to get hit eventually. Adequate protection starts at about 1" of steel plate if it's angled to the incoming projectiles.
Bob
On Oct 31, 2010, at 8:56 AM, Michael Baker wrote:
Hello, Time-Nutters--
A real-world precision timing need:
As a dedicated long-range rifle shooter and
ballistics enthusiast, I am in the early stages
of a project I am getting started on...
The object is to measure the velocity of a
rifle bullet both at the muzzle and downrange at
various distances up to 800 yards/meters or so.
Conventional optical sky-screens will will be
used for measuring the velocity at both ends.
However, I also need time-of-flight and this
requires knowing the timing relationship between
the time the bullet crosses the muzzle sky-screen
and the downrange sky-screen. Bullet muzzle velocities
will be between 1900 to 3200 feet-per-second.
Additionally, I will be using the output from an
array of 4 ultrasonic sensors located on the
corners of a 4-foot PVC pipe square to determine
the size of the shot group at the far end and
telemeter this info back to a laptop at the
shooting bench.
I can use a 10-MHz crystal for the sky-screen clocks
and the for the 4 ultrasonic bullet shot location
sensors. However, determining the time-of-flight is
a more difficult task as this requires syncing clocks
together at both ends to a moderate degree of accuracy.
Out to 100 yards I can send the time-of-flight
far-end pulse back by wire and compare it to the
muzzle-end sky-screen pulse but this is not practical
to do by wire out at 800 yards.
This project is on a tight budget-- namely, MY
wallet, so cost is a major concern. Suggestions
will be most welcome!!
Thanks!!
Mike Baker
Gainesville, Florida, USA
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
On Oct 31, 2010, at 8:06 AM, Bob Camp wrote:
Adequate protection starts at about 1" of steel plate if it's angled to the incoming projectiles.
Using hardened armor plate (as used for steel "gong" targets) can get that down under a half inch, resulting in a lot less mass to drag downrange and back. It won't hurt to locate the sensor behind a berm, either. The sky screen and/or its supports will still get shot eventually, but that will be a lot cheaper to replace than the sensor.
--
Mark J. Blair, NF6X nf6x@nf6x.net
Web page: http://www.nf6x.net/
GnuPG public key available from my web page.
Hi Mike:
Are you looking into the Pejsa Ballistics computations?
http://www.prc68.com/I/FNFAL.shtml#Bal
Have Fun,
Brooke Clarke
http://www.PRC68.com
Michael Baker wrote:
Hello, Time-Nutters--
A real-world precision timing need:
As a dedicated long-range rifle shooter and
ballistics enthusiast, I am in the early stages
of a project I am getting started on...
The object is to measure the velocity of a
rifle bullet both at the muzzle and downrange at
various distances up to 800 yards/meters or so.
Conventional optical sky-screens will will be
used for measuring the velocity at both ends.
However, I also need time-of-flight and this
requires knowing the timing relationship between
the time the bullet crosses the muzzle sky-screen
and the downrange sky-screen. Bullet muzzle velocities
will be between 1900 to 3200 feet-per-second.
Additionally, I will be using the output from an
array of 4 ultrasonic sensors located on the
corners of a 4-foot PVC pipe square to determine
the size of the shot group at the far end and
telemeter this info back to a laptop at the
shooting bench.
I can use a 10-MHz crystal for the sky-screen clocks
and the for the 4 ultrasonic bullet shot location
sensors. However, determining the time-of-flight is
a more difficult task as this requires syncing clocks
together at both ends to a moderate degree of accuracy.
Out to 100 yards I can send the time-of-flight
far-end pulse back by wire and compare it to the
muzzle-end sky-screen pulse but this is not practical
to do by wire out at 800 yards.
This project is on a tight budget-- namely, MY
wallet, so cost is a major concern. Suggestions
will be most welcome!!
Thanks!!
Mike Baker
Gainesville, Florida, USA
---------------------------------
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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--
Have Fun,
Brooke Clarke
http://www.PRC68.com
Hi
The gotcha is that the gong can move / twist when hit. The plate buried in front of the electronics has to just sit there and take it. More energy transfer to the anchored plate.
I'm sure there are alloys that will get you under 1", the issue will be making sure you have the right one...
Bob
On Oct 31, 2010, at 4:44 PM, Mark J. Blair wrote:
On Oct 31, 2010, at 8:06 AM, Bob Camp wrote:
Adequate protection starts at about 1" of steel plate if it's angled to the incoming projectiles.
Using hardened armor plate (as used for steel "gong" targets) can get that down under a half inch, resulting in a lot less mass to drag downrange and back. It won't hurt to locate the sensor behind a berm, either. The sky screen and/or its supports will still get shot eventually, but that will be a lot cheaper to replace than the sensor.
--
Mark J. Blair, NF6X nf6x@nf6x.net
Web page: http://www.nf6x.net/
GnuPG public key available from my web page.
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