ElectricAye said...
Well, I'm trying to illustrate how gravity is not really the same thing as acceleration, though the units are the same and in some cases you can use the same kind of instrumentation to measure both.
Sorry, man, it is the same thing, insofar as the two are equivalent and completely indistinguisable from a measurement standpoint. In all cases, the instrumentation, in principle, is the same. The difference between a sharp knock and a steady gravitational pull is one of degree, not of substance. That said, there may well be accelerometers that are damped to be insensitive to brief, but intense impacts. And an undamped 50g-max accelerometer will certainly get "pinned" and, perhaps, damaged if subjected to a 100g knock, however brief. But again, these are all differences of nothing more fundamental than intensity and duration.
BTW, I'm not trying to pick an argument — especially on Christmas Eve, perish the thought! It's just physics, after all. You can read more about Equivalence here.
-Phil
Post Edited (Phil Pilgrim (PhiPi)) : 12/25/2008 12:23:43 AM GMT
Gravitational acceleration is·similar to inertial acceleration, but it is also different.· The weight we feel on earth is actually caused by the equal and opposite force of the ground pushing up on us.· This force cancels out the gravitational force, which produces a net acceleration of zero.· Remove the force of the ground and we will accelerate toward the center of the earth with an increase in speed of·32 feet/second·per second.· We will feel weightless in this case.
When we are stationary on the ground, an accelerometer will measure an acceleration of 1 G.· If the accelerometer were dropped from a height, it will measure an acceleration of zero, even though its speed is increasing·toward the ground at 32 fps per second.· In free space, away from any gravitational forces, the accelerometer will·show an acceleration of zero, and it will maintain a constant speed.· If a rocket engine were fired that produced 1 G of acceleration, the accelerometer would report 1 G.· In this case, the accelerometer would be increasing its speed by 32 fps per second.· This would feel the same as 1 G of gravity on the earth's surface, but the effect on the change in speed is different.
So from the perspective of the accelerometer (or a human for that matter) we need to know the value and direction of the gravitational field to determine the inertial motion based on the measurements from·an accelerometer.
...the two are equivalent and completely indistinguisable from a measurement standpoint. In all cases, the instrumentation, in principle, is the same.
Phil, make Einstein's elevator infinitesimally small so there's no gradient to worry about, and I'll climb inside and.... oh well.... nevermind....
Contemplating the Equivalence Principle reminds me of why I punted physics and backslid into engineering. I had a room mate who was a pure theoretician. His speciality was determining how many holes a surface could have.
"Isn't it infinite?" I said.
"Well," he said snidely, "There's more than one kind of infinity."
"Huh?" I said. "I thought infinity was infinity. How the heck you get more than infinity?"
"Like this" he said, and made two curly marks on a blank sheet of paper.
He was a genius.
Last I heard, he created a black hole. And he and his pencil were sucked out of the universe.
Along more prosaic lines... Specifications for shock are not necessarily specified as mere acceleration. Sometimes engineers use the concept of jerk, which is the derivative of acceleration with respect to time. (In rare cases, there's even a second derivative of acceleration, but I don't recall its name). If Bambino's accelerometer isn't designed to get jerked around so it can measure shock, could it be pegging out and sucking up current momentarily and thus causing his Propeller to crash? In other words, it might have been specified for a smooth centrifugal force of 500 G's, but it could actually be experiencing a jerk much higher than what it can stand and somehow shorts out. Since I don't have a schematic, I'm just tossing this out there.
Just a thought as I sit here watching other people watch TV on Christmas Eve.
This is beginning to look very much like a "How many angels can dance on the head of a pin" debate. Accelerations of that magnitude (2500G) are almost always generated by an impact (drop onto a hard surface) or an explosive device (ie artillery shell firing), and the accelerometers are designed to handle the forces involved. I am convinced the problem of the reset is with the electronics. It may be a connection, a wire bond, or a momentary short in a component but it will not be the accelerometer.
I thought you guys might need something to chew on so here's the sensor specs.
And Phil, I do declare. Christmas or no, Where's your Irish blood at today?
Dave, Thanks again for the tip on my battery pack. I would be testing today if not for hard drive failure's.
Thank god for backup's.
As for angels and pins. LOL That might be a little off topic, but any debate on gravity is a worth while read. If I every get this project to market I have some Memsic devices I'd like to play with. That 1G sitting still concept gets my curiosity up every time.
Angel's and infinity, Reminds me of the zoom feature in Autocad. I made a circle in college, zoomed in and made another, and another, class was over and I was still zooming in on that joker!
Nick, If your wondering what's taking my gadget gangsters project so long.....well.....I guess you've read this thread.........
Ellaborating a little more on this, the 50 g's that I have mentioned is determined from the material being dropped on.
We have different mats that deliver rough calabration of the impact expected. The 50 g's is expected when you drop the missle on a wrestling mat. Tests so far are not even using the accelorometer on the device. I am using the ADAC to read the battery voltage at a high rate to increase the current use of the circuit to a value higher than what will normally be seen by the device in a drop. If the counter starts over then I know I have had a reset. So in reality what I am asking has nothing to do with the accelerometer, but rather where the reset is coming from. And I am betting that has already been answered, if I can just get my software reloaded I'll know.
No offense to Beau or Phil, but I am hopeing dave is right about the Battery pack, as the crystal will mean having to produce more boards. Of course adding a bigger capacitor might incur a board layout revision as well!
Those altimeters can take a pretty good beating and still work. I know quite a few people - some sitting in this very chair - who have crashed this one and still flew it again:
You can get a pretty good look at the construction from the photos there. It won't survive a lawndart, but if a parachute tangles or even strips right off, you've got a pretty good chance to save the electronics if the nosecone came off and you're not simply coming in ballistic. What's most likely to cause damage is a battery that rips loose from its moorings and strikes the board, not anything on the board itself. These things are put together with a pretty standard technique. Small parts surface-mounted to a board can take a lot of rough treatment. It's those large parts that are fastened down some other way that give you the problems.
500 g's? How do you expect to incur a 500g load? There was a stock car (or Formula-1 car) that hit a wall head-on at top speed, and it peaked at 212 g's. 50g is within the limit of survivability of most circuits, assuming you soldered everything really well (and put some big caps upstream of the voltage regulator). But even at 50g, 6AA batteries is already 16lbs of "weight". (.86oz x 6 x 50g / 16oz/lb = 16.125lb). At 500g, that goes up to 161.25lb (and that's ignoring the dynamic response of the system, which could increase or decrease that value based on the structure.
I want to thank Carl and PhiPi for reminding me of Einstein's role in all of this talk about accelerations and gravity. After growing old and flabby, my brain has turned to dust and forgotten all of that advanced physics stuff, which I never learned anyway.
In any case, Carl and PhiPi have renewed my curiosity, and because all this talk about Einstein's elevator is way, way off topic even for the Sandbox, I've started a thread on the Physics Forum so I can try to get a clue about this gravity = acceleration thing. Come visit!
Dave, only the accelerometer needs to be connected directly to the missile in order to measure the acceleration. The batteries and electronics can be in a shock absorbing mount that would reduce the G force to much lower levels.
Sorry for hijacking this thread, but it is somewhat applicable to my question. I dropped my PPDB upside down with a SparkFun 5DF board on it, now the Z axis of the accelerometer is putting out no voltage. Would a drop of < 2' be enough to kill it?
Usually when the military fires a rocket its a one time affair. Some times the video you see is VIA fiber cable (gulf war1 video) they don't get the rocket back to examine on board video equipment. gps guided units generally don't require video. If you want to see 500g's you may have to build one shot units (unless your the government) it can get quite expensive. Or try encasing everything in fiberglass resin and have external (cable fed) power.
Hi Guys,
O to 500 G's is just the federal minimum needed criteria. A typical drop is around 100 and can go to around 300.
Phil, your wager was correct. I ran the device at RCFAST with no difference, it still reset. I then cross wired the switch so that the charger circuit could directly run the propeller. With constant power from the wall wort it survived everything I dared throw at it. Which was a·thin pad over asphalt. I'll hopefully get another test routine in it and get it to the lab for testing later this week.
Meanwhile I practice soldiered a couple batteries together without splattering my shop with acid.(Some things are just a good plus!) I didn't test direct power with the PLL and crystal running, but that will be the first thing to shoot for.
As for the shock incurred by cars during accidents, I don't know what to tell you other than they are made to buffer the impact. My device simply measures the buffering of the substance it's dropped on. Without buffering the impact of 20lbs onto solid concrete for instance has only been done once with my devices predicessor which has no onboard devices other than the accelorometer. It peaked out the sensor and clipped the bell curve of data we normally see from a drop.
Jay, my accelorometer isn't a memsic device, so I don't have an answer for you. I can say that the propeller has servived the drops I have made so far. Which are in excess of 2 g's. But since memsic devices are not as solid state as controllers I have my doubts. At least I have been lead to believe that they have a liquid inside they use to correlate their position.·Maybe someone·knows better the concept MEMSIC than I(I certainly hope so).
ElectricAye said...
"Huh?" I said. "I thought infinity was infinity. How the heck you get more than infinity?"
Easy:
A. Imagine writing down an infinitely long list of all the real numbers, you know floats like 1.08083....
B. In another column next to this list number each of the entries of the first list using integers 1,2,3,4.....
Now we have something that looks like:
.
.
53 1.4333
.
.
09480 980398.098983
.
.
With many entries missing here.
C. As it's an infinite list we have used all the integers to do this.
D. BUT we can always create a new float number that is NOT in the list.
E. Conclusion there are infinitely more real numbers than integers
For Step D create the new number by writing down the first digit of the first float + 1, then the second digit of the second float +1 etc etc. The number you are writing is clearly different from every existing number in the list so far.
Another way to think of this is that between any pair of adjacent integers like 48 and 49 there must be an infinate number of fractional steps like 48.923847....
Turns out here are an infinite number of different sized infinities.......
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
For me, the past is not over yet.
thanks for illustrating this to me. It's interesting stuff, but you'll have to forgive my ignorance (and emotionally-based abandonment) of such arguments. I suppose my emotional brain is more sympathetic to arguments expressed in the following:
At a glance, this sort of thing feels to me like Zeno's paradox, in which reason can lead the mind down one alley while reality (whatever that is) does whatever it wants to.
I'm not saying this isn't useful stuff. Math is an outrageously powerful tool. But with respect to what it says about reality, I just wonder sometimes if it's not some kind of super-expansive incredibly self-consistent system of BS.
I confess it's all above my paygrade, which is why I fell out of grace with pure physics and degenerated into engineering. Since then, I've been wallowing in my own kind of Night of the Iguana.
Just an update for those interested. I removed the inner padding and reprogrammed to use the crystal. The device has withstood everything we intend to throw at it. No exact data yet on the G's it handles, but we have tested it near 400 without incurring a reset.
Thanks all for your help. Because of the way the springs where parrallel with ground I never would have suspected them as being the problem.
Now if I can just find some rechargables that don't quit on me at 0 degrees celcius I'll be real close to market!
Comments
BTW, I'm not trying to pick an argument — especially on Christmas Eve, perish the thought! It's just physics, after all.
-Phil
Post Edited (Phil Pilgrim (PhiPi)) : 12/25/2008 12:23:43 AM GMT
When we are stationary on the ground, an accelerometer will measure an acceleration of 1 G.· If the accelerometer were dropped from a height, it will measure an acceleration of zero, even though its speed is increasing·toward the ground at 32 fps per second.· In free space, away from any gravitational forces, the accelerometer will·show an acceleration of zero, and it will maintain a constant speed.· If a rocket engine were fired that produced 1 G of acceleration, the accelerometer would report 1 G.· In this case, the accelerometer would be increasing its speed by 32 fps per second.· This would feel the same as 1 G of gravity on the earth's surface, but the effect on the change in speed is different.
So from the perspective of the accelerometer (or a human for that matter) we need to know the value and direction of the gravitational field to determine the inertial motion based on the measurements from·an accelerometer.
Dave
·
Phil, make Einstein's elevator infinitesimally small so there's no gradient to worry about, and I'll climb inside and.... oh well.... nevermind....
Contemplating the Equivalence Principle reminds me of why I punted physics and backslid into engineering. I had a room mate who was a pure theoretician. His speciality was determining how many holes a surface could have.
"Isn't it infinite?" I said.
"Well," he said snidely, "There's more than one kind of infinity."
"Huh?" I said. "I thought infinity was infinity. How the heck you get more than infinity?"
"Like this" he said, and made two curly marks on a blank sheet of paper.
He was a genius.
Last I heard, he created a black hole. And he and his pencil were sucked out of the universe.
Along more prosaic lines... Specifications for shock are not necessarily specified as mere acceleration. Sometimes engineers use the concept of jerk, which is the derivative of acceleration with respect to time. (In rare cases, there's even a second derivative of acceleration, but I don't recall its name). If Bambino's accelerometer isn't designed to get jerked around so it can measure shock, could it be pegging out and sucking up current momentarily and thus causing his Propeller to crash? In other words, it might have been specified for a smooth centrifugal force of 500 G's, but it could actually be experiencing a jerk much higher than what it can stand and somehow shorts out. Since I don't have a schematic, I'm just tossing this out there.
Just a thought as I sit here watching other people watch TV on Christmas Eve.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
· -- Carl, nn5i@arrl.net
And Phil, I do declare. Christmas or no, Where's your Irish blood at today?
Dave, Thanks again for the tip on my battery pack. I would be testing today if not for hard drive failure's.
Thank god for backup's.
As for angels and pins. LOL That might be a little off topic, but any debate on gravity is a worth while read. If I every get this project to market I have some Memsic devices I'd like to play with. That 1G sitting still concept gets my curiosity up every time.
Angel's and infinity, Reminds me of the zoom feature in Autocad. I made a circle in college, zoomed in and made another, and another, class was over and I was still zooming in on that joker!
Nick, If your wondering what's taking my gadget gangsters project so long.....well.....I guess you've read this thread.........
We have different mats that deliver rough calabration of the impact expected. The 50 g's is expected when you drop the missle on a wrestling mat. Tests so far are not even using the accelorometer on the device. I am using the ADAC to read the battery voltage at a high rate to increase the current use of the circuit to a value higher than what will normally be seen by the device in a drop. If the counter starts over then I know I have had a reset. So in reality what I am asking has nothing to do with the accelerometer, but rather where the reset is coming from. And I am betting that has already been answered, if I can just get my software reloaded I'll know.
No offense to Beau or Phil, but I am hopeing dave is right about the Battery pack, as the crystal will mean having to produce more boards. Of course adding a bigger capacitor might incur a board layout revision as well!
Meanwhile, I must accelerate towards Christmas dinner!
-Phil
Those altimeters can take a pretty good beating and still work. I know quite a few people - some sitting in this very chair - who have crashed this one and still flew it again:
68.178.208.82/cgi/PF_Store/perlshop.cgi?ACTION=enter&thispage=MAWD.html&ORDER_ID=!ORDERID!
You can get a pretty good look at the construction from the photos there. It won't survive a lawndart, but if a parachute tangles or even strips right off, you've got a pretty good chance to save the electronics if the nosecone came off and you're not simply coming in ballistic. What's most likely to cause damage is a battery that rips loose from its moorings and strikes the board, not anything on the board itself. These things are put together with a pretty standard technique. Small parts surface-mounted to a board can take a lot of rough treatment. It's those large parts that are fastened down some other way that give you the problems.
No accelerations for me anymore, thanks to Einstein I'm simply going to gravitate toward my mashed potatoes.
gravity = acceleration
g = a
jerk = da/dt
jerk = dg/dt?
What da heck is dg/dt???
-Phil
Finally! That explains it. I always wondered what that strange feeling was.
Hope that helps,
Dave
In any case, Carl and PhiPi have renewed my curiosity, and because all this talk about Einstein's elevator is way, way off topic even for the Sandbox, I've started a thread on the Physics Forum so I can try to get a clue about this gravity = acceleration thing. Come visit!
www.physicsforums.com/showthread.php?p=2014781#post2014781
Good Luck
O to 500 G's is just the federal minimum needed criteria. A typical drop is around 100 and can go to around 300.
Phil, your wager was correct. I ran the device at RCFAST with no difference, it still reset. I then cross wired the switch so that the charger circuit could directly run the propeller. With constant power from the wall wort it survived everything I dared throw at it. Which was a·thin pad over asphalt. I'll hopefully get another test routine in it and get it to the lab for testing later this week.
Meanwhile I practice soldiered a couple batteries together without splattering my shop with acid.(Some things are just a good plus!) I didn't test direct power with the PLL and crystal running, but that will be the first thing to shoot for.
As for the shock incurred by cars during accidents, I don't know what to tell you other than they are made to buffer the impact. My device simply measures the buffering of the substance it's dropped on. Without buffering the impact of 20lbs onto solid concrete for instance has only been done once with my devices predicessor which has no onboard devices other than the accelorometer. It peaked out the sensor and clipped the bell curve of data we normally see from a drop.
Jay, my accelorometer isn't a memsic device, so I don't have an answer for you. I can say that the propeller has servived the drops I have made so far. Which are in excess of 2 g's. But since memsic devices are not as solid state as controllers I have my doubts. At least I have been lead to believe that they have a liquid inside they use to correlate their position.·Maybe someone·knows better the concept MEMSIC than I(I certainly hope so).
Easy:
A. Imagine writing down an infinitely long list of all the real numbers, you know floats like 1.08083....
B. In another column next to this list number each of the entries of the first list using integers 1,2,3,4.....
Now we have something that looks like:
.
.
53 1.4333
.
.
09480 980398.098983
.
.
With many entries missing here.
C. As it's an infinite list we have used all the integers to do this.
D. BUT we can always create a new float number that is NOT in the list.
E. Conclusion there are infinitely more real numbers than integers
For Step D create the new number by writing down the first digit of the first float + 1, then the second digit of the second float +1 etc etc. The number you are writing is clearly different from every existing number in the list so far.
For more rigorous explanation see here en.wikipedia.org/wiki/Cantor%27s_diagonal_argument
Another way to think of this is that between any pair of adjacent integers like 48 and 49 there must be an infinate number of fractional steps like 48.923847....
Turns out here are an infinite number of different sized infinities.......
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
For me, the past is not over yet.
thanks for illustrating this to me. It's interesting stuff, but you'll have to forgive my ignorance (and emotionally-based abandonment) of such arguments. I suppose my emotional brain is more sympathetic to arguments expressed in the following:
en.wikipedia.org/wiki/Controversy_over_Cantor%27s_theory
At a glance, this sort of thing feels to me like Zeno's paradox, in which reason can lead the mind down one alley while reality (whatever that is) does whatever it wants to.
I'm not saying this isn't useful stuff. Math is an outrageously powerful tool. But with respect to what it says about reality, I just wonder sometimes if it's not some kind of super-expansive incredibly self-consistent system of BS.
I confess it's all above my paygrade, which is why I fell out of grace with pure physics and degenerated into engineering. Since then, I've been wallowing in my own kind of Night of the Iguana.
May Cantor have mercy on my soul...
Thanks all for your help. Because of the way the springs where parrallel with ground I never would have suspected them as being the problem.
Now if I can just find some rechargables that don't quit on me at 0 degrees celcius I'll be real close to market!