sorry for asking

[ADWSystems]

I agree, there's no need for absolute numbers, just relative ones - and even trying to do the maths is going to be wildly inaccurate anyway, as how do you measure most of the values in the first place?.

What values are you interested in measuring? I have the weight, size, and design of the target, and the mass of the soccer ball and can measure the acceleration. Knowing the proper force equation for target will give one of two results.
Either:
1. The actual answer (ie., is the target was actually F=ma=1/2mV2, then I can solve for V knowing everything else)
or
2. A formula based on the distance from the connection (hinge point if you will) to the point of impact. From which, I can then evaluate the value from the impact at the top edge versus the bottom edge to see the magnitude of change due to difference.

 

[rjenkinsgb]

How does the mass of an object change by hitting something?

It does not - but the total mass of the ball does not all impact at the same instant; the initial impact deforms it and the energy transfer is spread out over time.

Having thought about it more, the peak acceleration is almost irrelevant; it could be extremely high for microseconds or moderate for milliseconds and transfer the same amount of kinetic energy.

You need to in effect integrate the force vs time to sum the impact energy.
eg. That could be as simple as sampling at 100KHz and adding all the sample values over the duration of the impact.

 

[ADWSystems]

You need to in effect integrate the force vs time to sum the impact energy.

Sure, no problem. Do you have the equation to convert the acceleration measured into force so I can add it up?

 

[rjenkinsgb]

eg. That could be as simple as sampling at 100KHz and adding all the sample values over the duration of the impact.

...

 

[ADWSystems]

eg. That could be as simple as sampling at 100KHz and adding all the sample values over the duration of the impact.

How do I use the accelerometer samples values to sum force versus time?

 

[dknguyen]

I did mention the 999 scale is the digital output of the 10 bit ADC with the last 25 counts dropped. I'm hoping the off-center distance makes little difference to the resulting values, but that can't be know without knowing the force equation for the target.


How to you plan to get, setup, and power all this sh-stuff in the middle of a soccer field?

This system has to be built to be transported to, set up, and powered in a soccer field anyways so I don't see the issue. Your're claiming that it's too cumbersome to test the system in the way it's meant to be used. You don't even need a soccer field. You don't have a backyard or an grassy opening where you can just wail the ball at the target?

There's no point in trying to get into these nitty gritty equations when you don't even know if something so important as being off-center won't mess up all the assumptions these equations are making. Your missing the forest for the trees here.

the rest of what you have said is predicated on know the speed of the ball as you seem to be working with the same 1 equation and two unknowns. Having the second equation solves the problem (pun intended and not).

What is the second unknown? What else do you care about other than the ball speed and the fact it hit the target? Is it force? Why would you need to know that if you choose to measure speed directly? Force is instrinsically tied to speed in this case. Like I said, you're missing the forest for the trees. How is a ball going to hit the target at a given speed twice, but hit it softer one time and harder another time? Especially if the target is essentially always going to be horizontal and the same distance from the shooter? Even if the distance was highly variable and you wanted an impact force readout, it would be meaningless unless your system took into account how far away the shooter was.

 

[ADWSystems]

There's no point in trying to get into these nitty gritty equations when you don't even know if something so important as being off-center won't mess up all the assumptions these equations are making. Your missing the forest for the trees here.

And you have the cart before the horse. Find the equations and we can determine the effect of a high impact on the target versus a low impact on the target. I am quite certain the equation will include the distance from the pivot point.

What is the second unknown? What else do you care about other than the ball speed and the fact it hit the target? Is it force? Why would you need to know that if you choose to measure speed directly? Force is instrinsically tied to speed in this case. Like I said, you're missing the forest for the trees.

Do you know the force? I don't. Do you know the speed? I don't. On the free floating target you have F=ma and F=1/2mV2. Since you don't want want to use the target you have only F=1/2mV2 where you know neither F nor v. 1 equation, 2 knowns.

I don't care IF the ball hits the target. The ball must hit the target to produce a reading. The reading is acceleration. The only way I have to determine force is from acceleration through the equation that knows seems to know.

How is a ball going to hit the target at a given speed twice, but hit it softer one time and harder another time? Especially if the target is essentially always going to be horizontal and the same distance from the shooter? Even if the distance was highly variable and you wanted an impact force readout, it would be meaningless unless your system took into account how far away the shooter was.

The target is NEVER going to be horizontal. It will ALWAYS be vertical. As for the rest, ???

 

[ADWSystems]

18.9 m/s if hit at the bottom edge with the sensor at the bottom edge. Dropping ratiometrically as the point of impact moves from the bottom edge to the top edge (distance from top edge to point of impact : distance from top edge to point of impact). If you assume that most shots are on center then most readings will be cut in half.

Assume hits will follow a similar pattern as rifle shots, and move away from the target in a sinusoidal or exponential drop off. then most reading will be most accurate by placing the sensor in the middle of the target.

 

[Pommie]

If you had an optical system working then doesn't it make sense to debug that? A laser diode will be much brighter than the sun, combining a filter plus edge detection should be able to eliminate false triggers. For a "belt and braces" approach you could use small mirrors to guide the laser to a dark place - if need be, turn it through 180°.

Mike

 

[ADWSystems]

If you had an optical system working then doesn't it make sense to debug that? A laser diode will be much brighter than the sun, combining a filter plus edge detection should be able to eliminate false triggers. For a "belt and braces" approach you could use small mirrors to guide the laser to a dark place - if need be, turn it through 180°.

Mike

I didn't think so. It worked indoors and couldn't see a solid piece of paper outside. Granted I was using only one diode and one matched IR sensor (supposedly most sensitive to the laser wavelength). But I can't debug what I can't see.

I can debug the accelerometer much easier. I had it working on the first try (OK second try, I forgot the power supply for the display on the first try). The OP was quite straightforward but for some reason everyone is so hell bent to redesign/design by committee. Once I figured out the correct words to punch into google the exact answer was presented.

 

[ADWSystems]

I didn't think so. It worked indoors and couldn't see a solid piece of paper outside. Granted I was using only one diode and one matched IR sensor (supposedly most sensitive to the laser wavelength). But I can't debug what I can't see.

I can debug the accelerometer much easier. I had it working on the first try (OK second try, I forgot the power supply for the display on the first try). The OP was quite straightforward but for some reason everyone is so hell bent to redesign/design by committee. Once I figured out the correct words to punch into google the exact answer was presented.

 

[Pommie]

Sounds to me that the way you are going has far more debugging required than an optical system. However, each to their own.

Mike.

 

[ADWSystems]

Sounds to me that the way you are going has far more debugging required than an optical system. However, each to their own.

Mike.

Apparently I'm missing something. What is there to debug? The system worked second try. I got readings first time on target. I just needed the college level physics equation to do some math.

I liked the optical system as I could more quickly check for digital inputs than to get numbers from ADC conversions.

 

[dknguyen]

And you have the cart before the horse. Find the equations and we can determine the effect of a high impact on the target versus a low impact on the target. I am quite certain the equation will include the distance from the pivot point.

Do you know the force? I don't. Do you know the speed? I don't. On the free floating target you have F=ma and F=1/2mV2. Since you don't want want to use the target you have only F=1/2mV2 where you know neither F nor v. 1 equation, 2 knowns.

No. You are the one putting the cart before the horse. What you're doing right now is similar to building a simulator, and then assuming it will reflect reality without actually comparing it to reality. The fact you have no idea what the numbers should be or what variables you can and cannot ignore is testament to this. In theory, theory matches reality. In reality, it doesn't. Even simple measurements of well known things under controlled conditions at the lab here rarely match up with the math.

I don't care IF the ball hits the target. The ball must hit the target to produce a reading. The reading is acceleration. The only way I have to determine force is from acceleration through the equation that knows seems to know.

Like I said before, speed is tied to the impact force and much easier to measure and interpret directly. You may not want to do it that way for practical reasons involved with the hardware and that's fine. However, I think you are vastly underestimating how reality doesn't always match up with pure math. Mount an accelerometer to the backside of the board and throw a few balls at it at different speeds and angles. I guarantee you the acceleration waveform that you get is a lot messier than you seem to think it will be. So messy it may not even be worth working with, or at least not worth working with on an equation level. If you have already seen the acceleration waveforms for a bunch of kicks, fine, but I somehow don't think you have.

Note that I'm talking about acceleration waveforms here as in a graph unless you have already verified that you can get reliable and consistent peak acceleration readings under most conditions and angles of shots (and soccer balls of different tolerable inflations for that matter). To get a graph of those readings you would either need to scope the accelerometer or have the processor sample and save the data and then spit it out to the PC so you can graph it in a spreadsheet program.

What processor are you planning on using BTW?

How do I use the accelerometer samples values to sum force versus time?

If you try this, you definitely will need to observe the graphs of the acceleration waveforms to know if your results are reliable and to handle any unexpected weirdness in the nature of the curves (like biases, noise, and bandwidth issues). Look up "numerical integration", "numerical methods", and/or numerical methods. These can be processor intensive so you need to make sure your processor can cope.

The target is NEVER going to be horizontal. It will ALWAYS be vertical. As for the rest, ???

Huh? The target is going to be directly above or below the player? I don't think you understood what I was saying. When I say the target is horizontal to the shooter, I don't mean the orientation of the target board. I mean the line between the player and target.

The OP was quite straightforward but for some reason everyone is so hell bent to redesign/design by committee.

That's what happens when you go to a group of people who know what they're doing and ask about how to go about things in the wrong way. We get questions like this all the time.

 

[Pommie]

What is there to debug?

Obviously nothing, you've got it all worked out. No need for any more questions or answers.

Mike.

 

[Dr_Doggy]

the flaw would be that the wood would swing at different rates depending on elevation of the ball on impact, even with the same velocity ,... notice that it is easier to push the wood and make it move at the bottom than at the top

may i suggest a chronograph type of detector

 

[ADWSystems]

No. You are the one putting the cart before the horse. What you're doing right now is similar to building a simulator, and then assuming it will reflect reality without actually comparing it to reality. The fact you have no idea what the numbers should be or what variables you can and cannot ignore is testament to this. In theory, theory matches reality. In reality, it doesn't. Even simple measurements of well known things under controlled conditions at the lab here rarely match up with the math.

My horse already pulled the cart and left.

Like I said before, speed is tied to the impact force and much easier to measure and interpret. You may not want to do it that way for practical reasons involved with the hardware and that's fine. However, I think you are vastly underestimating how reality doesn't always match up with pure math. You seem unwilling to do any testing so you would not know this.

It would appear you have succumbed to TLDR. Since I have posted the readings from the working system with the accelerometer.

Mount an accelerometer to the backside of the board and throw a few balls at it at different speeds and angles.

I did but since the speed is unknown what is the point? I have acceleration readings. What do you want to do with those?

I guarantee you the acceleration waveform that you get is a lot messier than you seem to think it will be. So messy it may not even be worth working with, or at least working with on an equation level. If you have already seen the acceleration waveforms for a bunch of kicks, fine. But from your mentioning of it being too tough to set it up in the field, I doubt it.

Guess the jokes on you. The waveform is purty. I don't have the data any longer to post a picture. I looked at it to verify the accelerometer was not picking up noise and to verify the expected waveform. I didn't need it any beyond that so I didn't spend the effort to try to store it. Looks like a ringing sine wave but starts with a VERY vertical rising edge. Only three samples (four if you also count the starting at rest measurement) on the rising edge and 10x that on the falling edge.

What processor are you planning on using BTW?

Not planing. Am using. Arduino UNO ATMEGA328P ISR Method, 10k sample rate.

Huh? The target is going to be directly above or below the player? I don't think you understood what I was saying. When I say the target is horizontal to the shooter, I don't mean the orientation of the target board. I mean the line between the player and target.

OK. we missed on that one.

That's what happens when you go to a group of people who know what they're doing and ask about how to do something in an impractical way. We get questions like this all the time.

Completely practical and doable, and furthermore, done.

You all do realize this is exactly how the professionals determine the impact velocity of long range (sniper) rifle shots, right?

 

[ADWSystems]

the flaw would be that the wood would swing at different rates depending on elevation of the ball on impact, even with the same velocity ,... notice that it is easier to push the wood and make it move at the bottom than at the top

Already noted, see post #28. The force applied and the acceleration experienced is ratiometric.

 

[dknguyen]

Guess the jokes on you. The waveform is purty. I don't have the data any longer to post a picture. I looked at it to verify the accelerometer was not picking up noise and to verify the expected waveform. I didn't need it any beyond that so I didn't spend the effort to try to store it. Looks like a ringing sine wave but starts with a VERY vertical rising edge. Only three samples (four if you also count the starting at rest measurement) on the rising edge and 10x that on the falling edge.

That's great news. I assume the sine wave is just due the board swinging back and forth which isn't important.

Not planing. Am using. Arduino UNO ATMEGA328P ISR Method, 10k sample rate.

If you do want to do the signal processing stuff to squeeze more out of your data you would have to scope and zoom in on that spike more and the Arduino might also have to sample faster to get the shape and characteristics of that spike that's actually responsible for the ball impact.

If you try that, an Arduino might not cut it if you want to do real-time signal processing stuff. But since soccer balls aren't being shot at it continuously it might be just enough if you can store the data and do calculations. The time between samples needs to be sufficiently frequent and known, however, and if the Arduino software layer gets in the way of that then.

Of course, it's needless if you actually do get clean reliable peak accelerations that you can use.

Not planing. Am using. Arduino UNO ATMEGA328P ISR Method, 10k sample rate.

You're not done yet if you're still working on the most difficult part.

You all do realize this is exactly how the professionals determine the impact velocity of long range (sniper) rifle shots, right?

And the army uses digital video for their UAVs. That doesn't mean I do with mine. Different levels of manpower and resources warrant different approaches. Remember that I never said it was not possible, just that there were easier methods. Test with a speed gun and see how well it actually works.

 

[dknguyen]

Question about your math though. Why are you going

F=mA as well as F=1/2*mV2.

One is force, the other is kinetic energy, so really it should be E = 1/2*m*(v^2).