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mdrejhon

Re: [RMURRAY] Vigil Status report

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>A tumbling (or rotating) body will show very funky readings from the
>accelerometer.

Not really. A tumbling body with a three-axis accelerometer at the center of mass will show gravity normal force as a vector sum of the three accelerometer measurement angles (assuming the body's speed isn't changing.) As you move away from the center, it will also show centripedal normal force due to the rotation. The good news there is that a 3-axis accelerometer mounted on the opposite side of the CG will show the opposite acceleration, and thus can be nulled.

But all of that is somewhat overkill. The utility in an accelerometer that I see is twofold -

1) If you are not moving, and haven't been moving much at all according to the accelerometer, and the barometric sensor sees a sudden 1000 foot change - it's probably spurious, and firing should probably be delayed.

2) If you are in freefall, and are going through 1000 feet, and see a sudden single axis 2G acceleration over a few seconds, your main parachute is probably opening. So best to delay firing under those conditions.

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The good news there is that a 3-axis accelerometer mounted on the opposite side of the CG will show the opposite acceleration, and thus can be nulled.

The pros will have to figure out how to compensate for this kind of stuff, but one could theoretically put different axes of the accelerometer witin different areas of the same case (i.e. AAD casing). Then the center of gravity can be extrapolated this way from calculations from the different centripetal forces from different accelerometers inside the same casing or same chip. Or, theoretically even different corners of a single 3D chip component, if an accelerometer became sufficiently accurate enough to distinguish small differences in this centripetal force. Then it might not matter where the single "box" or "chip" (filled with accelerometers) was placed on a tumbling person. The mathematicians will have to deal with this; it's a little beyond my ballpark, and there are certain limitations, but as far as I know, tumbling can certainly be compensated for. There are many variables like a tumbling body that's rapidly accelerating or decelerating, such as a swooper doing funky tricks. So, that does complicate things.

It's all complicated right now, but so was GPS electronics twenty years ago, bulky electronics with many chips. Now GPS is a single computer chip that outputs easily-decodable location information that even a High School computer programmer (with some basic high school Geography class knowledge) can understand. The smallness and improved simplicity of GPS electronics are why they are used in many cellphones now. I can buy a GPS chip, put it into a science fair type of project, and I don't even need to care shit about what complex math is going on inside the GPS -- today, I'd only care about the simple serial text output (NMEA standard) from the GPS chip that outputs lat/long/altitude information once a second. Who'd thought GPS would be simple enough that it'd be built into cellphones back then?

The innovation handheld GPS units and other compact GPS is forcing improvements and innovations in accelerometer usage. Eventually, it is possible handheld GPS units would have accelerometers, and still dead-reckon properly even if the handheld unit is tumbling (such as a GPS unit attached to the hip or wrist, where it's rocking all over the place, or to a mountain bike handlebar). Once this happens, they may be accurate and simple enough for AAD's that it is no longer a KISS violation.

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Rotation will read as rotation...nothing funky about that.



So would you explain how a 3-axis accelerometer would be able to sense rotation? During acceleration and rotation all you will read is 3 m/s^2 parameters varying. If the body is completely in vacum, the sum of the 3 vectors is be equal to g. But that is not even close to the conditions near terminal.

rgds,
Stefan

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The innovation handheld GPS units and other compact GPS is forcing improvements and innovations in accelerometer usage. Eventually, it is possible handheld GPS units would have accelerometers, and still dead-reckon properly even if the handheld unit is tumbling (such as a GPS unit attached to the hip or wrist, where it's rocking all over the place, or to a mountain bike handlebar). Once this happens, they may be accurate and simple enough for AAD's that it is no longer a KISS violation.



I have jump with mechanical AAD. The gadget you propose is way to long complicated and its an overshoot. KISS

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Why not put a GPS receiver in an AAD too? That should be able to tell you your altitude above MSL to within 10m or so and could compensate for DZ elevation at the same time the ground level is zeroed to ambient air pressure. Belts, braces,etc...



GPS isn't all that fast or accurate for elevation. And when the plane takes off, you almost certainly don't have a lock on position.

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I have jump with mechanical AAD. The gadget you propose is way to long complicated and its an overshoot. KISS

It may be right now, but it may not be in the future.

Be noted that there are millions transistors in some of the chips that go into some of the newer AAD's, yet they still manage to KISS. The truth, is that there is more computing power in, say, a Vigil AAD, than the full-room ENIAC computer in the 1940's. It wasn't KISS back then.

A full "computer screen" on an AAD (the Vigil LCD), heaven forbid - That's a KISS violation back in the old engineer days. Now it is relatively simple today to have a display screen like that these days, in a watch, a cellphone, an MP3 player, or whatnot. Such display driver silicon typically hundreds of thousands of transistors, often millions, in what used to be mind-bogglingly complicated electronics circuitry. Why complicate things, and perhaps leave the screen off the AAD? Let's KISS.

It may never happen, but it's amazing how complicated what electronics inside an AAD, used to be in the old days. It's incredible the amount of effort that goes into designing a chip. Even though off-the-shelf chip components are often standardized and used in many products (i.e. the same chip that in say a digital camera, is often also used in an MP3 player -- such as an LCD screen driver chip) now, it can't be ignored that the initial design of the chip is an enormously complex undertaking in the first place.

and often nowadays, many the AAD manufacturers just use well-tested off-the-shelf chips mixed with only just a few custom components.

I may look young (32), but I have been computer programming for 20 years (started age 11), so I have a good concept of how things that used to be complex, are relatively simple today. I also have some basic electronics knowledge background, and understand the concept of silicon AND, NAND, OR, NOR, NOT circuitry, along with capacitors, resistors, etc. I'm more computer programmer now, but I appreciate the computing that goes inside a chip that powers an AAD, or that powers a GPS, or any other thing.

Who knows - tomorrow a freefall trajectory tracker might output very simple numeric vector values, from a single-chip-package multi-axis rotation-compensating accelerometer chip. By then such chips could have been well-tested for 10 or 15 years in consumer products such as dead-reckoning in handheld GPS units and GPS-equipped cellphones. Obviously, it would have to be very simple, massmarket single-chip plug-and-play (to an engineer) solution, before it happens. And that time, then it wouldn't be a KISS violation.

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I may look young (32), but I have been computer programming for 20 years (started age 11), so I have a good concept of how things that used to be complex, are relatively simple today.



I'm sorry I'm not getting into this pissing contest.

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Who knows - tomorrow a freefall trajectory tracker might output very simple numeric vector values, from a single-chip-package multi-axis rotation-compensating accelerometer chip. By then such chips could have been well-tested for 10 or 15 years in consumer products such as dead-reckoning in handheld GPS units and GPS-equipped cellphones. Obviously, it would have to be very simple, massmarket single-chip plug-and-play (to an engineer) solution, before it happens. And that time, then it wouldn't be a KISS violation.



I don't think so. Does current (electronical) AADs working fine? Yes, if they are used in their operational envelope. They can make a good decision from the current source of data. Anyway do not forget if manufacturers can save $2 on one unit they will.

I like cool gadgets too, but not in my life saving device.

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I'm sorry I'm not getting into this pissing contest.

It isn't a pissing contest. I don't see one here. :)
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I don't think so. Does current (electronical) AADs working fine? Yes, if they are used in their operational envelope. They can make a good decision from the current source of data. Anyway do not forget if manufacturers can save $2 on one unit they will.

That's true. If misfire incidents don't happen, it could very well be. On the other hand, if misfires happen a lot more, that $2 on that extra chip allows them to make a few extra boasts that may cause a few AAD purchases. (Some buy Vigil because of the no "scheduled" maintenance marketing talk or another reason, others buy Cypres for their time tested reptuation or another reason, etc). It's a tradeoff between additional cost and additional marketability, that may be totally dependant on component prices and future misfire incidents. One example, is, my perception is that we are getting bigger and bigger recreational skydiving aircraft compared to 20 years ago, and more and more of them are pressurized-capable. Pilots still make procedural mistakes too. And what's the state of skydiving in 20 years? (and other swooping and 2-out related disasters that might ultimately be preventable). We don't know.

We do know though, today's environments are slowly becoming increasingly more complicated for yesterday's AAD's, and tomorrow's might be even more problematic. (Swooping, pressurizable aircraft, wingsuits, future technologies, etc) Requiring even more smarts in tomorrow's AAD's, if too many incidents of all kinds (both fatal and benign) gradually start happening. We don't know if that will happen or not.

Because this is a discussion relating to the future, I think we can now just let this thread die, as the points have been made by all parties (your and my points are both equally valid, IMHO), and see what prevails in 15-20 years from now.

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I like cool gadgets too, but not in my life saving device.

Same here too. We both agree on that. I prefer time tested trustability, so I wouldn't trust an accelerometer *today* either.

Personally, I depend (or, rather, "hope") on my Cypres2 to save me if I'm incapitated for any reason (and I hope to never need it). It still has 9 perfectly good years left in it, and I plan to use all of those years, assuming I stay in the sport. So I'm not in a rush for any new AAD either.

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That's true. If misfire incidents don't happen, it could very well be. On the other hand, if misfires happen a lot more, that $2 on that extra chip allows them to make a few extra boasts that may cause a few AAD purchases. (Some buy Vigil because of the no "scheduled" maintenance marketing talk or another reason, others buy Cypres for their time tested reptuation or another reason, etc).


There was a good comparison of AADs and their costs in the Skydiving magazine.

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(Swooping, pressurizable aircraft, wingsuits, future technologies, etc)


How many times have you ever jumped from a pressurized AC?

We don't need complicated systems. You should be decide in no time if you are going to be in activation range or not.

What is wrong? A pilot failed to execute rigth procedures? A swooper was pushing its limits?

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2nd, why to fix something ain't broken?

It's not about something that is broken and it is not about fixing something. Your words.

It's not about fixing something that is broken - it is about improvement through time tested technology but only when it becomes more trustworthy than without, and right now it's too early to tell the direction skydiving and AAD's will be in 20 years from now. You are right that there isn't really a need NOW. But I am saying the potential is there to need improvement in the FUTURE. Remember we can't accurately predict 20 years into the future. Not me either.

Please remember technologies have a knack of simplifying over time. While today's complex computers, such as Windows-based systems, crashes a lot and/or put up a lot of problems, you have to remember that computers more complex than complicated full size room 1950's computers are routinely in wristwatches, elevator control electronics, modern pacemakers, medical machines, even a wireline phone headset, etc. (Even a simple caller display chip with display, for example, contains more computing power than a 1940's room size computer).

It is the point of the point of time-tested technology that start to become more trustworthy with it than without, where it's clearly and easily an improvement by virtual unamious opinion, rather than a scary complicated add-on with unproven track record that makes a gadget more complicated and more crashprone (like a Windows computer collecting an infestation of viruses and spyware, or hardware problems such as dirt clogging the CPU fan, etc.). Obviously some predicted technologies, such as the vaunted 1950's nuclear engine for never-have-to-refuel cars, never came to fruitition -- now that we all know how horrendously complicated and dangerous nuclear reactors are. (It is interesting to note that *Current* trends of accelerometers, appear to be going in the direction of simplification, not complexification.)

One of the many great examples of "complex technology undergoes simplification" is the wristwatch, comparing digital versus analog. A mechanical analog wristwatch is orders of magnitude simpler in terms of number of parts, but typically more unreliable, does not keep time as accurately, and requires more maintenance. A digital wristwatch contains greatly over 10,000 separate parts (counting each individual transitor on a chip) that were designed in a specific way one way or another by humans. Yet remarkably ends up being more reliable, more inexpensive, and more accurate nowadays. In fact, today it is now harder to design an analog wristwatch than a digital wristwatch, because a university Electronics engineer (or even high school Electronics student) can more easily put together off-the-shelf parts for a custom digital wristwatch than an analog watch of the same size. It's remarkable how complex technologies gradually, over time, becomes simple. To a watch engineer, a off-the-shelf wristwatch chip is just one additional part that was previously designed and tested for years by other chip engineers - this engineer doesn't need to have an understanding of each transitor inside the watch chip, just need a basic understanding of the generic logic, protocol, and/or now-familiar programming language the particular chip uses. Likewise, as technologies simplify themselves into easily manipulatable parcels (single copmonents), they become easier building blocks, even though each individual building block (chip) is very complex inside.

And yes, I'm definitely aware that a hugely evil side exists in a complicated gadget, but I am also aware with how certain former complex technologies end up becoming time tested super-reliable, greatly simplified into a single time-tested off-the-shelf component, and very well-integrated into society with a proven track record and easy for a low-wage engineer to work with. Whether you're stepping into an elevator or you're glancing at a wristwatch.

Anyway, this thread is yours -- enjoy -- I'm just letting this thread die as I think excellent good points have been successfully made by multiple parties (yourself included too).

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