What would be the cost/difficulty of setting up an accelerometer into a target

[dvcochran]

The interpretation of data was included in my initial post...

Hence, peak reading.

Have a known weight, held by a known resistance that is attached to something that can induce a voltage (let's say, a magnet on a spring in a coil), run the output of that "sensor" through a buffer to record the peak value, display that value however you please.

With known variables you can calibrate that display in whatever units you so desire - Newtons, kgf, psi, squirrels...

Adding the capability to display force over time on a graphical display is more complex, but not necessarily required.

A completely analogue version could be an airtight bag with a lump of foam in, with a valved outlet to a tube containing a tennis ball held by friction - kick the bag, the harder you hit the further the ball goes and stays put to allow recording of results. Not a great resolution, not fantastic repeatability, but would still allow comparison between people or over time and even slack tolerance calibration.

Yes, but as soon as you add the buffer to record and the display you are way past pennies, unless of course you have them laying around.

 

[pdg]

Yes, but as soon as you add the buffer to record and the display you are way past pennies, unless of course you have them laying around.

By 'buffer' all I mean is something to register and hold the peak voltage for long enough to pass it to the display, which can be a very small handful of discrete components.

Using that, something like an arduino or probably even a pi can be 'simply' programmed to hold and display that peak (the buffer would only be required because I don't think either would have a fast enough sample rate). Who hasn't got that sort of thing laying around?

The actual display itself (the bit you look at) could be anything from an LED segmented display through to a pc monitor.

So, while not pennies in the absolute strictest sense of the word, it'd be a few quid.

And yeah, not exactly industrial quality - but a reasonable toy.

 

[jobo]

They're different types of force. Just like I said, which you said was wrong, then said I was wrong to say they're different because you say they're different.

You'd probably wear ballet shoes to go hiking if someone said they were unsuitable (well, you'd say you did, but change the subject if asked for evidence).

Then you'd proclaim how wrong that person was because you'd decided ballet shoes aren't suitable for hiking.

Bored now.

Yoh always get bored when your wrong if you want tosplit hairs, there are 4 fundamental forces, gravity,,electromagnetic and the strong and weak nuclear forces that govern partial interactions .

However, we were discussing Newtonian mechanics, laws of motion etal, in which case there is only one force, the types to which you refers are just different ways in which it is applied,

 

[Dirty Dog]

So, a phone accelerometer.

Is it useful?

I got an accelerometer app, switched it on, tucked my phone in my sock (like on the kick comparison video, kinda) and kicked a wall with nowhere near my full capacity.

I exceeded the range of the sensors.

In other words, off the fricken scale.

In other other words, my kick is more powerful than a drag car without me even putting any serious effort in



Edit: the figures at the top are live, that's how much movement was occurring to take the screenshot.

Pretty much irrelevant.
As usual for me, when issues such as this are brought up, I sought out expert opinion. In this case, one of our kids. He's got his BS and MS in mechanical engineering and is working on his PhD. His day job includes measuring impact forces for the rail industry. When he's not blowing up trains for the feds.

1 - You don't measure impact from the object moving, you do it from the object being struck.
2 - We looked up the specs on the accelerometers used in the iPhone. They're capable of measuring +/- 2000 G acceleration with the right code, but the Apple people have limited their code to +/- 2 G. Aftermarket apps could access any degree of that capability. At +/- 2G, the accuracy is 0.018 G, which will go down slightly if you're measuring higher G forces, but it'll still be within 0.1 G. More than accurate enough for our purposes, especially since there's no rational reason why we'd need 2000 G sensitivity.
3 - We downloaded an app for both my iPhone and his Android phone.
4 - With that app, both were capable of measuring 10 G accelerations, as measured by throwing the phones onto my couch with a moderate amount of force. We did not max out their capabilities. We were going to throw them a little harder, but my dog thought we were throwing them for him to fetch, so we stopped.
5 - Your foot has no significant mass, and your sock is not a stable platform, given how stretchy socks are.
6 - Strap that phone to a 100 lb heavy bag, and 10 G of acceleration will require an impact of about 1000 lbs. Using a common 130 lb heavy bag, that impact will be about 1300 lbs.

While you could certainly spend as much money as you like to reach whatever level of accuracy you desire, I think this is more than adequate for our purposes.
Ideally, I think you'd want a custom app, so you can input the weight of the bag you're strapping the phone to. To go with that, you'd want a case for the phone with a strap for the bag. Add a target that's directly opposite the phone, if you like.
Results would vary depending on the accuracy of the strike; a strike that goes directly into the target will deliver more power than one that angles across the bag (as I'm sure we all know).
If you want to increase the accuracy, you could also include math to account for the fact that a hanging bag doesn't move in a straight line when it's struck, but I doubt the difference is important.

 

[pdg]

If you want to increase the accuracy, you could also include math to account for the fact that a hanging bag doesn't move in a straight line when it's struck, but I doubt the difference is important.

More important would be the deformation of the bag when struck, which you'd have to account for if you want accuracy. Think like holding a kick shield, you do not receive the full force of the impact - so unless you kick the phone directly the measurement will be off.

This would actually help with having the sensor/app capable of measuring the force without maxing out.


But, attaching it to my foot was the direct comparison to sticking it in a car.

The standard apps can and do cope with what a car can throw at them, but not what a foot can do, which was my point from the beginning.

 

[Dirty Dog]

More important would be the deformation of the bag when struck, which you'd have to account for if you want accuracy. Think like holding a kick shield, you do not receive the full force of the impact - so unless you kick the phone directly the measurement will be off.

Something like a 130 lb heavy bag doesn't deform all that much. And if the strap used to secure it is something like a ratchet strap, it's going to be further compressed to the point that it doesn't really deform at all, since you'll be striking the area that's already compressed.

 

[pdg]

Something like a 130 lb heavy bag doesn't deform all that much. And if the strap used to secure it is something like a ratchet strap, it's going to be further compressed to the point that it doesn't really deform at all, since you'll be striking the area that's already compressed.

So if that's the case, get a heavy bag. Wrap some straps around it. As many as you like, as tight as you like.

Now recreate your avatar pic with the bag laying on top of those blocks.

If your statement that a bag doesn't deform enough to have any effect is true, you'll break them all.

Or.

Stand holding a heavy bag. Get someone to kick it with full force.

Now move away from the bag and have them kick you.

Must feel identical, right?



Any deformation at all absorbs/disperses energy - that's why a half inch of padding on a dashboard is less likely to cave in your skull in an accident compared to the old fashioned painted steel.

 

[pdg]

We looked up the specs on the accelerometers used in the iPhone. They're capable of measuring +/- 2000 G acceleration with the right code,

Citation required...

Data sheets for the bosch and inventec devices used in the iPhone 6 state available ranges of +/-2, 4, 8, 16 G.

(The inventec device may be slightly different, as it's believed to be a 6700 series chip, but the closest data available is for the 6500)

Also, you're looking at the heavy bag scenarios wrong.

You're making the assumption that the measurement relies on the entire mass of the bag moving. That's forgetting applied force against duration.

A good kick on a heavy bag might see it deform (dent) and bend, with a swing. A moderate poke with one finger could swing it the same amount.

Using purely displacement of the entire mass (which your scenario implies) the work done is identical - the same mass has moved the same distance.

So does poke = kick?

Yes and no.


Note how I'm not saying Mr. Masters degree in engineering is incorrect, just that his analysis of the situation is incomplete in this particular instance (or that your relaying of his information is).

 

[Dirty Dog]

You're making the assumption that the measurement relies on the entire mass of the bag moving. That's forgetting applied force against duration.

A good kick on a heavy bag might see it deform (dent) and bend, with a swing. A moderate poke with one finger could swing it the same amount.

You're confusing distance moved with rate of acceleration.

 

[pdg]

You're confusing distance moved with rate of acceleration.

Well, no, not really.

For something to be said to be accelerating (i.e. have a change in velocity over time), there must be a time component. If that time component is taken to be zero, no acceleration can be taking place.

Because of that, distance is a necessary component. Accelerate anything for any time and it must by definition cover distance.

Let's look at a previous statement.

Frankly, if you think your kicks move things more abruptly than a hard launch at the drag strip, you've just never been in a car that launches hard.

This one.

And, let's take into account your use of "g".

So, a Lamborghini Aventador.

Fairly quick car, no? 0-60 in 2.7 seconds. Must be high numbers?

1g of horizontal acceleration. One. Singular.

So, let's up it. Go to funny cars, they're quick right?

Standing start to 335mph in 3.8 seconds maybe?

4g.

So, go top fuel, reduce the timeframe to just 0-100mph. 0.85 seconds.

5.36g.

Hmm.

So I kick a football (a round one). I can probably get that thing going 60mph. A nice comparable 0-60.

As I kick it, it deforms slightly and moves. I'll be exceedingly generous and say my foot is in contact for 0.1 seconds (one tenth of a second, probably overestimating by at least a factor of ten, but let's not make the car look too bad).

27.35g.

Compare that to being able to throw the same ball at 60mph. Hold it in both hands behind your head and overhand throw it. It starts accelerating when your hands start to move, and reaches it's peak velocity when you let go.

Half a second? Actually, let's say a quarter.

10g.

But it's the same ball, achieving the same acceleration...

Over a different time.


In summary, measuring the force of a kick is subject to so many variables that it's essentially a pointless exercise to try and put these sorts of numbers on them. If you want accuracy then you need more than one number as a result if you want to compare.

 

[pdg]

Actually, additional.

Putting one number on for comparison can be used, if everyone is working with the same variables.

The issue is that as soon as you change one of the variables, the result changes and you get "this kick is better than that kick".

In the capoeira kick video that initiated this whole thing, the only two kicks that can be viably compared were the tkd guy and the mt guy, because they were the most similar. In that instance, the results showed that the tkd guy performed better.

It doesn't show that one type is better.

Change the measurement variables (i.e. use actual science) and the capoeira guy could have viably 'won' (instead of the fake win by introducing the bs "hidden technique")

The karate guy could've won it too, if the timeframe was increased to highlight the advantages of his chosen kick.

 

[dvcochran]

So if that's the case, get a heavy bag. Wrap some straps around it. As many as you like, as tight as you like.

Now recreate your avatar pic with the bag laying on top of those blocks.

If your statement that a bag doesn't deform enough to have any effect is true, you'll break them all.

Or.

Stand holding a heavy bag. Get someone to kick it with full force.

Now move away from the bag and have them kick you.

Must feel identical, right?



Any deformation at all absorbs/disperses energy - that's why a half inch of padding on a dashboard is less likely to cave in your skull in an accident compared to the old fashioned painted steel.

I agree with you both. The measurement must be recorded from the impact not the motion. The sensor should be aa close to the impact as possible to factor out anomalies such as deflection and bag weight.
When we measure vibration which is the same sensor, it is attached directly to what item you are measuring, e.g. bearings, pumps, shafts, etc... The farther away you get form the source of the measurement, the harder it is to accurately interpret the data. Yes, it is done routinely but knowing all the other effective signals can be tough. And they can change over time.

 

[Gerry Seymour]

How is it different? Acceleration is acceleration. I don't see that it really makes any difference if the acceleration is from a rocket, a car engine, or a kick.

I suspect (no data to back up this suspicion) that there are more G's in a kick than in a launch. The launch lasts longer, so probably much more total energy transferred. I've no idea what the range of the sensors is, so it might be moot - if the kick is within the same order of magnitude, then I'd expect the sensors to be capable of measuring/reporting it. Then you'd just need to protect the phone, itself.

 

[pdg]

suspect (no data to back up this suspicion) that there are more G's in a kick than in a launch

I supplied figures for some comparison purposes above.

 

[dvcochran]

Actually, additional.

Putting one number on for comparison can be used, if everyone is working with the same variables.

The issue is that as soon as you change one of the variables, the result changes and you get "this kick is better than that kick".

In the capoeira kick video that initiated this whole thing, the only two kicks that can be viably compared were the tkd guy and the mt guy, because they were the most similar. In that instance, the results showed that the tkd guy performed better.

It doesn't show that one type is better.

Change the measurement variables (i.e. use actual science) and the capoeira guy could have viably 'won' (instead of the fake win by introducing the bs "hidden technique")

The karate guy could've won it too, if the timeframe was increased to highlight the advantages of his chosen kick.

I made this argument very early on in the thread. The front kick used as part of the sample skews the data greatly. It was used to create the "data" the video was trying to produce. Very misleading to the uniformed viewer.

 

[dvcochran]

All the banter said, @Dirty Dog 's phone app and strap solution would be very cheap and could easily be accurate enough by sampling kicks and results on the heavy bag. I don't think it would be truly scalar because low results (weak kicks) should be affected more by the weight of the bag. Trial and error should produce a decent scale to use. If you were not too worried about your phone and strapped a kicking target to the bag with the phone between them I feel certain the results would be more accurate and easier to scale.
This is pretty cool; Monnit has a Bluetooth coin cell accelerometer that has a few options. I did not research it very much so it would be interesting if there is an app to grab the data. Samples every 10 seconds so I think that would work pretty good and it if works, it would save your phone from damage.

 

[Gerry Seymour]

All the banter said, @Dirty Dog 's phone app and strap solution would be very cheap and could easily be accurate enough by sampling kicks and results on the heavy bag. I don't think it would be truly scalar because low results (weak kicks) should be affected more by the weight of the bag. Trial and error should produce a decent scale to use. If you were not too worried about your phone and strapped a kicking target to the bag with the phone between them I feel certain the results would be more accurate and easier to scale.
This is pretty cool; Monnit has a Bluetooth coin cell accelerometer that has a few options. I did not research it very much so it would be interesting if there is an app to grab the data. Samples every 10 seconds so I think that would work pretty good and it if works, it would save your phone from damage.

I agree. In fact, if we wanted to account for the fact that some kicks would move the bag less (more of the force goes into deforming), we could add a second test with a lighter target (hand target, double-ended bag, or some such) that would give us a second set of data points to look at.

If the point is to examine each type of kick in isolation and look for improvement, the heavy bag with the phone on the back is probably enough (I'd probably opt for a lighter bag - maybe 70 lbs.). If we want to compare different kicks, we probably need at least a second type of test.

 

[pdg]

Monnit has a Bluetooth coin cell accelerometer that has a few options. I did not research it very much so it would be interesting if there is an app to grab the data. Samples every 10 seconds

Got a link?

If it's a 10 second sampling rate, that'd be pointless for this as you'd have to time your kick to the sample (which is highly unlikely).

If it has a sensible sampling rate (at least 50hz) and burst transmits every 10 seconds, that'd work...

 

[Gerry Seymour]

..

 

[dvcochran]

Got a link?

If it's a 10 second sampling rate, that'd be pointless for this as you'd have to time your kick to the sample (which is highly unlikely).

If it has a sensible sampling rate (at least 50hz) and burst transmits every 10 seconds, that'd work...

just google monnit.com. Yes, I suppose it is looking for a continuous signal that it checks every 10 seconds. I did not look but you may be able to change settings.