Electronic Tuning?

P

patgarity

Guest
A recent post about electronic barrel tuners reserrected an old brain storm (fart?) that I had awhile back. I wondered if the tools used for diagnosing vibrations in cars would work on rifle barrels. What I'm talking about is a Vetronix MTS 4000 or an old EVA. These tools utilize an accelerometer and hand held computer (like a big gameboy) that reads G forces and vibration frequency. So today I went down to the garage set up my bullet trap and rigged up the tool and did some testing. With the gun rigged in the same trim that I shot this year (it sucked) I did some measurements. With the accelerometer perched on (magnetic base) the barrel just behind the tuner I was getting consistant readings of .096 g's and 3.25 hz. Then I took all the weights (the whole Von Ahrens set) off and retested. .106 G's and the exact same freq. 3.25. I was expecting a big change in the data. I was disapointed. I was hoping I could just add and subtract weight and spin the tuner until I found the sweet spot that produced the least amount of g's and frequency. I don't think that a hundredth of a G is significant. I'm thinkin' the old fashioned put holes in the paper method beats the high tech accelerometer. Anybody else tried this?:rolleyes:
 
What did the accelerometer and base weigh? This would affect the vibration. You readings are so far off the normal makes me suspect you weren't actually measuring vibration with much accuracy. Good idea though but you would always have to deal with quantum mechanics....any time you measure something you affect the measurement.
 
patgarity said:
A recent post about electronic barrel tuners reserrected an old brain storm (fart?) that I had awhile back. I wondered if the tools used for diagnosing vibrations in cars would work on rifle barrels. What I'm talking about is a Vetronix MTS 4000 or an old EVA. These tools utilize an accelerometer and hand held computer (like a big gameboy) that reads G forces and vibration frequency. So today I went down to the garage set up my bullet trap and rigged up the tool and did some testing. With the gun rigged in the same trim that I shot this year (it sucked) I did some measurements. With the accelerometer perched on (magnetic base) the barrel just behind the tuner I was getting consistant readings of .096 g's and 3.25 hz. Then I took all the weights (the whole Von Ahrens set) off and retested. .106 G's and the exact same freq. 3.25. I was expecting a big change in the data. I was disapointed. I was hoping I could just add and subtract weight and spin the tuner until I found the sweet spot that produced the least amount of g's and frequency. I don't think that a hundredth of a G is significant. I'm thinkin' the old fashioned put holes in the paper method beats the high tech accelerometer. Anybody else tried this?:rolleyes:
Click to expand...

Pat,
Cecil is right, your measurement of frequency seems low. The first harmonic should be around 100 Hz, depending on the barrel contour and length (see http://www.varmintal.com/amode.htm).

I don't know about a 22, but we measured acceleration (with a miniature glue-on accelerometer) on a 223 hunting rifle and the peaks were around 10 G's if I remember correctly. Since the 22 has a lighter bullet, about three times lower muzzle velocity and double the bullet exit time, I would guess peak acceleration should be about ten times smaller (assuming barrel acceleration scales with the bolt face force F = bullet mass x muzzle velocity/exit time), or about 1 G. Then tuner mass should affect the value relative to this approximate baseline.

The problem with this approach, which we did not recognize until we actually ran the experiments, is that the accelerometer does not measure what you really want to know. Since tuning amounts to synchronizing the bullet exit time to when the muzzle angle is rising, what you want to measure is the angle of the muzzle when the bullet exits. The vertical position and velocity of the muzzle also make a difference. Acceleration can, in principle, be integrated once to calculate velocity, and again to calculate position, but it cannot be used to find muzzle angle. Our measurements also showed that bullet exit time was indistinguishable in the acceleration plots. So until we can find a way to measure muzzle angle, I think you are right about "holes in the paper" being the best way to tune.

Cheers,
Keith
 
The barrel is telling you what mode it is in by it having a node behind the muzzle.
 
Pictures of the rig

I've never posted pics here but I'm gonna give it a shot........
 

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mks said:
Maybe something like this:
Click to expand...

Yes, and you cannot use indicators to measure barrel vibrations. Indicators have no time component to their measurement and cannot tell whether the bullet was in the barrel during its peak measurement or 100 yards down range.

With an indicator you dont know if the display measurement was the actual maximum barrel movement or even greater movement with the plunger being thrown off the barrel thru momentum.............Don
 
patgarity said:
A recent post about electronic barrel tuners reserrected an old brain storm (fart?) that I had awhile back. I wondered if the tools used for diagnosing vibrations in cars would work on rifle barrels. What I'm talking about is a Vetronix MTS 4000 or an old EVA. These tools utilize an accelerometer and hand held computer (like a big gameboy) that reads G forces and vibration frequency. So today I went down to the garage set up my bullet trap and rigged up the tool and did some testing. With the gun rigged in the same trim that I shot this year (it sucked) I did some measurements. With the accelerometer perched on (magnetic base) the barrel just behind the tuner I was getting consistant readings of .096 g's and 3.25 hz. Then I took all the weights (the whole Von Ahrens set) off and retested. .106 G's and the exact same freq. 3.25. I was expecting a big change in the data. I was disapointed. I was hoping I could just add and subtract weight and spin the tuner until I found the sweet spot that produced the least amount of g's and frequency. I don't think that a hundredth of a G is significant. I'm thinkin' the old fashioned put holes in the paper method beats the high tech accelerometer. Anybody else tried this?:rolleyes:
Click to expand...


Surprised the sensor even stayed on a stainless steel barrel with a magnetic attachment. 416 stainless steel has very poor mangetic attraction. You were more than likely measuring the resonance between the hard sensor magnetic attachment and the barrel and not the actual barrel movement itself.

Sensors should be epoxy attached in a high frequency, high g force application.

Even so, your final analysis about paper over accelerometers is probably correct..............Don
 
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