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Posted: 1/8/2015 11:36:15 AM EDT
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What does Arfcom know about these devices?
Is there anything that could be used on a rifle to record firing stresses that's relatively affordable? This may be the wrong forum, mods feel free to delete this, if you wish. 
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Not sure how tech savvy you are but I found this while googling "access accelerometer data in cell phone":
http://www.mathworks.com/matlabcentral/fileexchange/42821-android-sensor-data-acquisition-accelerometer-example Combine it with a phone case strapped to the stock, and it might be what you need. |
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An accelerometer is very good at measuring in one axis. Up and down, fore and aft, or left and right.
I imagine you are going to measure recoil? It will be fine for that. The better you can eliminate other axis influence (muzzle flip) the better information you will get. Hard part will be calculating the range of force you will see so you can spec the correct accel. I used to work with them measuring user interface vibration on autos. Fancy way to describe "how buzzy the steering wheel feels when the AC is on high" 
Used Bruel and Kjaer. Small , about the diameter of a dime and 1/4" tall. Lab grade stuff. Big bucks. those needed the accel, wire, transponders and recorder. It's been about 10 years since I've worked with them, but , like others have mentioned, tI bet here is an app for that. Years ago, I thought about using strain gauges laid along the outside of the barrel chamber to measure stresses for developing max handloads. Pie in the sky daydreams that I never acted on. |
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What does Arfcom know about these devices? Is there anything that could be used on a rifle to record firing stresses that's relatively affordable? This may be the wrong forum, mods feel free to delete this, if you wish. If you're doing some da-da-damn stuff more brutal than 300WM, 416REM ... the Optometrist Forum would tell you that over 45 year old folks should worry about retinal tears/detachments.
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I want it to measure movement, specifically recoil and counter recoil. Each direction would have to carry a sensitive axis and three axis or multiple axis accelerometers are available. Since they tend to have limits in terms of their frequency response range, you have to be careful to select the right type of accelerometer and charge amp for the task. The next issue you will encounter is recording and data processing. Acceleration is the second derivative of the position-time function, so you must record with enough fidelity to be able to integrate once for velocity-time and again for position-time. We now use several concurrent systems to study the dynamics of mechanisms that include laser based tracking. None of this stuff is cheap, by the way. Edit: You may be able to simplify your study by using a force cell in the recoil direction if felt recoil is all you need. If muzzle rise is also important, then you will be stuck with the complications. |
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Ive worked with high frequency accelerometers and strain gages in years gone by. Data recording and processing would be the expensive side of things.
I wonder if a high frequency pressure transducer coupled with something like a hydrocoil recoil system couldnt be done. I.e. measure force v. time directly and leave out all the integration steps. Still need very high frequency to get resolution. Its all over and done with in 3 or 4 milliseconds, even recording/processing to 10 khz is only going to get you 30 or 40 data points along the force curve. |
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Also ~ high frequency bbl strain gage systems are commercially available.
strain measurement system |
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Damnit Zia, I was going to call the manufacturer of my setup today to find out how I could set it up for what you're after. I forgot all about it, I'll set a reminder on my phone to call them Monday. The only problem I have right now is figuring out how to initialize the test, for concrete tests I have an instrumented hammer that the program recognizes and 'begins' the test when it sees and impulse from the hammer. Without using the hammer to smack your trigger, I'm not sure how I'd begin the test. I think they already have a way to do this as the instrumented hammer is an option that we purchased, not particularly required for the test.
I really wonder how that conversation is going to go... |
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Damnit Zia, I was going to call the manufacturer of my setup today to find out how I could set it up for what you're after. I forgot all about it, I'll set a reminder on my phone to call them Monday. The only problem I have right now is figuring out how to initialize the test, for concrete tests I have an instrumented hammer that the program recognizes and 'begins' the test when it sees and impulse from the hammer. Without using the hammer to smack your trigger, I'm not sure how I'd begin the test. I think they already have a way to do this as the instrumented hammer is an option that we purchased, not particularly required for the test. I really wonder how that conversation is going to go... You know what would also be pretty cool is to measure lock time. I'd bet the resolution is plenty fast enough on my tool to do that. |
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You know what would also be pretty cool is to measure lock time. I'd bet the resolution is plenty fast enough on my tool to do that. Quoted:
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Damnit Zia, I was going to call the manufacturer of my setup today to find out how I could set it up for what you're after. I forgot all about it, I'll set a reminder on my phone to call them Monday. The only problem I have right now is figuring out how to initialize the test, for concrete tests I have an instrumented hammer that the program recognizes and 'begins' the test when it sees and impulse from the hammer. Without using the hammer to smack your trigger, I'm not sure how I'd begin the test. I think they already have a way to do this as the instrumented hammer is an option that we purchased, not particularly required for the test. I really wonder how that conversation is going to go... You know what would also be pretty cool is to measure lock time. I'd bet the resolution is plenty fast enough on my tool to do that. That would be useful.
I forgot to IM you last night, it's all good.
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That would be useful.
I forgot to IM you last night, it's all good. Quoted:
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Damnit Zia, I was going to call the manufacturer of my setup today to find out how I could set it up for what you're after. I forgot all about it, I'll set a reminder on my phone to call them Monday. The only problem I have right now is figuring out how to initialize the test, for concrete tests I have an instrumented hammer that the program recognizes and 'begins' the test when it sees and impulse from the hammer. Without using the hammer to smack your trigger, I'm not sure how I'd begin the test. I think they already have a way to do this as the instrumented hammer is an option that we purchased, not particularly required for the test. I really wonder how that conversation is going to go... You know what would also be pretty cool is to measure lock time. I'd bet the resolution is plenty fast enough on my tool to do that. That would be useful.
I forgot to IM you last night, it's all good. I can also ask them what their rates are for renting the unit, I know they offer rentals but I've never done that as we purchased one for the company. Hopefully I can get the configuration figured out for you, maybe do a few test runs and iron out the details, then you can simply rent the tool for a couple of days and not have to dink around with it to get it set up right. The analysis software is small enough that I could probably email it to you. Feel free to remind me next week... I have a great memory but it's really really short. These other guys do a lot of rentals and getting the unit to initialize is easier, and you can also see the results immediately. On my unit you have to transfer the results to a PC in order to see anything, so it's harder to tell if you have a clean test result until you download the data and use their software. Great company to work with too, I'll call them. If you were closer I could probably get this done free for you... Have you been to the North Springs Shooting range here in Utah yet? Best range in the world, and even guys who have been to Ben Avery in AZ would agree. Maybe it's time for a range trip. PDI- PIT tester thingy |
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That test amounts to part of a modal ping test. You put a single shock function into something to get a transfer function. By comparing the frequency, amplitude, and phase of the response divided by the input, you get a reading on things like transmissibility or the presence of cracks.
Not exactly the same as a response study for recoil impulse. In fact, considerably different. If you are going to spend that kind of money, you may want to consider renting a high speed video analysis system and track some fiducial points against time. You would be able to calculate displacement, velocity, and acceleration from tracking points toward the stock and muzzle. If you combine it with force readings from a piezo load cell at the butt stock, you would have a good reading on recoil with a much smaller budget. |
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That wouldn't be a problem. If you are really focused on forces up at the scope, a decent single axis accelerometer would tell you enough to rank differences.
I agree that the scopes can take a beating. I have seen perfectly good highpower scopes get trashed by the impulse shape of a spring airgun. |
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That wouldn't be a problem. If you are really focused on forces up at the scope, a decent single axis accelerometer would tell you enough to rank differences. I agree that the scopes can take a beating. I have seen perfectly good highpower scopes get trashed by the impulse shape of a spring airgun. Which, due to the mass involved, is similar on a large AR. |
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Zia: you may want to check the book, Rifle Accuracy Facts, by Harold R. Vaughn. He did exactly what you are looking into and more.
The accelerometer and recording is one thing. Attachment to the gun / scope is another. A poor attachment can be like the scope with a poor scope ring. Good luck. Love to read your experimental result! |
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Which, due to the mass involved, is similar on a large AR. Quoted:
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That wouldn't be a problem. If you are really focused on forces up at the scope, a decent single axis accelerometer would tell you enough to rank differences. I agree that the scopes can take a beating. I have seen perfectly good highpower scopes get trashed by the impulse shape of a spring airgun. Which, due to the mass involved, is similar on a large AR. By counter recoil are you talking about the return slam from the bolt/carrier or the elastic counter recoil from the gun? |
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By counter recoil are you talking about the return slam from the bolt/carrier or the elastic counter recoil from the gun? Quoted:
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That wouldn't be a problem. If you are really focused on forces up at the scope, a decent single axis accelerometer would tell you enough to rank differences. I agree that the scopes can take a beating. I have seen perfectly good highpower scopes get trashed by the impulse shape of a spring airgun. Which, due to the mass involved, is similar on a large AR. By counter recoil are you talking about the return slam from the bolt/carrier or the elastic counter recoil from the gun? The return of the carrier. My terminology may no be exact. |
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Zia-
I called the manufacturer of my testing device, it looks to be pretty easy to configure it to wait and sense a change and begin recording, so you could simple install the accelererometor to the gun and when it sees a significant impulse it records it. However, their rental rates are insane. Over $1,000/week, they are in Denver and would ship the unit right to you. |
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if u wanna try it, just mount a smartphone to a rail and use an accelerometer app that records to a graph... Cell phone accelerometer sampling rate is somewhere between 5 and 100 hz depending on your phone and the software used. If you want to monitor accelerations of a firearm you probably need closer to 10khz to 20khz. at least a 100 times faster sampling than your cell phone. |
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Zia- I called the manufacturer of my testing device, it looks to be pretty easy to configure it to wait and sense a change and begin recording, so you could simple install the accelererometor to the gun and when it sees a significant impulse it records it. However, their rental rates are insane. Over $1,000/week, they are in Denver and would ship the unit right to you. Thanks for doing all that, but there's no way that's in the budget for this test. Perhaps down the road, though. |
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Thanks for doing all that, but there's no way that's in the budget for this test. Perhaps down the road, though. Quoted:
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Zia- I called the manufacturer of my testing device, it looks to be pretty easy to configure it to wait and sense a change and begin recording, so you could simple install the accelererometor to the gun and when it sees a significant impulse it records it. However, their rental rates are insane. Over $1,000/week, they are in Denver and would ship the unit right to you. Thanks for doing all that, but there's no way that's in the budget for this test. Perhaps down the road, though. Well if there is a chance of you getting to Utah I'd help you with the testing with my unit, otherwise it looks like you are back to trying to figure something out. Have you ever looked into Arurino? It's like Legos for big kids that want to make robots and other really cool stuff. I found this- Arduino Accelo |
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That price is out of line with my own experience, especially when it isn't even the right equipment.
An outfit called TMS (The Modal Shop) rents accelerometers and a price like that would cover multiple sensors with electronics for a month. In the end, you would still want to budge at least $1k to rent the right instruments because even if you don't run them for a month, you still need to remember data acquisition costs if you don't already own one. A laptop with the right DAQ card running LabView can do a decent job, but so can a storage scope or DPO. The specifications for a decent general purpose accelerometer that is capable of recording the type of dynamic event from firearms that will cause scope damage are shown on the web sites from companies like B&K, PCB, Endevco, and the like. I see used ones on EBay going for several hundred dollars, without the charge amps. Self contained units that have a built in signal conditioner also exist, but are bulky and start to affect the measurement. Laser tracking equipment can also be rented, but their minimums are high compared to this discussion. |
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Relatively affordable... Nah. You're looking at a pretty expensive device for DAQ any way you slice, I think.
Now, to provide an alternative, because engineers solve problems, you don't need an accelerometer at all -- although it would make DAQ super easy. 1) Get your digital camera or go-pro with sufficient frame capture rates to create so-mo video. 2) Mark reference points on your rifle 3) Create a checkerboard 4) Bang away on the rifle with checkerboard adjacent to the rifle and everything perpendicular to view of the camera 5) Calculate whatever you want based on capture rate and distance reference point travels from video, easy, just time consuming Used in about a million mythbusters episodes. |
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Relatively affordable... Nah. You're looking at a pretty expensive device for DAQ any way you slice, I think. Now, to provide an alternative, because engineers solve problems, you don't need an accelerometer at all -- although it would make DAQ super easy. 1) Get your digital camera or go-pro with sufficient frame capture rates to create so-mo video. 2) Mark reference points on your rifle 3) Create a checkerboard 4) Bang away on the rifle with checkerboard adjacent to the rifle and everything perpendicular to view of the camera 5) Calculate whatever you want based on capture rate and distance reference point travels from video, easy, just time consuming Used in about a million mythbusters episodes. While this is a nice and cheap way of watching recoil for comparisons, what he's trying to do is measure how much FORWARD force an AR makes as it slams a new round in the chamber. I'm assuming he's also hoping to experiment with differing weights of buffers and springs to see what kind of backwards loads the scope encounters. I'm not sure you could get much from a chart an camera for that. |
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Ive worked with high frequency accelerometers and strain gages in years gone by. Data recording and processing would be the expensive side of things. I wonder if a high frequency pressure transducer coupled with something like a hydrocoil recoil system couldnt be done. I.e. measure force v. time directly and leave out all the integration steps. Still need very high frequency to get resolution. Its all over and done with in 3 or 4 milliseconds, even recording/processing to 10 khz is only going to get you 30 or 40 data points along the force curve. Piezoelectric pressure sensors for $400, Alex. |
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While this is a nice and cheap way of watching recoil for comparisons, what he's trying to do is measure how much FORWARD force an AR makes as it slams a new round in the chamber. I'm assuming he's also hoping to experiment with differing weights of buffers and springs to see what kind of backwards loads the scope encounters. I'm not sure you could get much from a chart an camera for that. Quoted:
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Relatively affordable... Nah. You're looking at a pretty expensive device for DAQ any way you slice, I think. Now, to provide an alternative, because engineers solve problems, you don't need an accelerometer at all -- although it would make DAQ super easy. 1) Get your digital camera or go-pro with sufficient frame capture rates to create so-mo video. 2) Mark reference points on your rifle 3) Create a checkerboard 4) Bang away on the rifle with checkerboard adjacent to the rifle and everything perpendicular to view of the camera 5) Calculate whatever you want based on capture rate and distance reference point travels from video, easy, just time consuming Used in about a million mythbusters episodes. While this is a nice and cheap way of watching recoil for comparisons, what he's trying to do is measure how much FORWARD force an AR makes as it slams a new round in the chamber. I'm assuming he's also hoping to experiment with differing weights of buffers and springs to see what kind of backwards loads the scope encounters. I'm not sure you could get much from a chart an camera for that. That is indeed my biggest area of interest. |
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While this is a nice and cheap way of watching recoil for comparisons, what he's trying to do is measure how much FORWARD force an AR makes as it slams a new round in the chamber. I'm assuming he's also hoping to experiment with differing weights of buffers and springs to see what kind of backwards loads the scope encounters. I'm not sure you could get much from a chart an camera for that. Quoted:
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Relatively affordable... Nah. You're looking at a pretty expensive device for DAQ any way you slice, I think. Now, to provide an alternative, because engineers solve problems, you don't need an accelerometer at all -- although it would make DAQ super easy. 1) Get your digital camera or go-pro with sufficient frame capture rates to create so-mo video. 2) Mark reference points on your rifle 3) Create a checkerboard 4) Bang away on the rifle with checkerboard adjacent to the rifle and everything perpendicular to view of the camera 5) Calculate whatever you want based on capture rate and distance reference point travels from video, easy, just time consuming Used in about a million mythbusters episodes. While this is a nice and cheap way of watching recoil for comparisons, what he's trying to do is measure how much FORWARD force an AR makes as it slams a new round in the chamber. I'm assuming he's also hoping to experiment with differing weights of buffers and springs to see what kind of backwards loads the scope encounters. I'm not sure you could get much from a chart an camera for that. Depends how fine the chart is, and how freely the rifle is allowed to recoil. Piezoelectric sensors are pretty cheap, but you still need a DAQ device with pretty high resolution. |
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