On Fri, 03 Dec 2004 01:31:11 -0500, "J. Clarke"
wrote:

wrote:
(Much snippage throughout)

On Thu, 02 Dec 2004 10:14:46 -0500, "J. Clarke"
wrote:

wrote:

On 01 Dec 2004 09:35:47 GMT, otforme (Charlie Self)
wrote:



Huh? How is it used in artillery shells?

Guidance systems.
See

http://www.smalltimes.com/document_d...ment_id=470 1

I don't recall if the information made it into the finished article,
but the next step is a guidance system that costs a few hundred
dollars per unit and fits in a NATO standard fuze well. That guidance
system will include the active elements (pop-out fins), an intertial
sensing system, control electronics, actuators for the active elements
and possibly a GPS system as well.

I can see where MEMS might be useful for the gyros, but how is it used in
the fin actuators?

I don't know that it will be. But that doesn't effect my original
statement that MEMS devices are tough enough to be used in artillery
stills. (Not all of them, but not everything has to take the 5000 Gs
that's the reference acelleration for an artillery projectile in the
tube.

Unless it is.

It might be, but the odds are against it. The expense lies in
fabricating these things. Our experience with these kinds of materials
is that the prices drop sharply as we learn how to make them and the
volumes increase. We're still at the beginning of this particular
roller coaster ride, but we're already seeing this happen.

The price per square inch doesn't drop appreciably, the price per part drops
as more can be fitted into a square inch.

Well, no. There are economies of scale as well as a learning curve to
consider. (Not to mention amortization of equipment.) And it is untrue
that more parts can necessarily be fitted into each square inch.
You're neglecting the growth in die size in things like
microprocessors as they become more complex and more powerful. The
cost decreases hold true even though the feature size has been
dropping like a rock. If you were to hold the feature size, and hence
the die size constant, you'd get at least a factor of 10 improvement
in price per square inch over the first generation parts.

You need a certain amount of surface area to cut wood.
Absolutely true, as far as it goes.

That means that any macroscopic woodworking tool
based on this technology is going to be expensive.

Nope. You're assuming the whole tool is made of active elements. Of
course it won't be any more than a desktop PC is made entirely of
microprocessors.

In fact the tool I'm envisioning is cheap because it is built light,
low precision parts. The accuracy comes from the sensors, processors
and actuators built into it.

Fabricating these devices and materials is closer to making simple
semiconductors than anything else. In fact most of the technology for
fabricating this stuff is adapted from semiconductor manufacturing.
The same kinds of economies of learning and scale apply.

And low cost then relies on high density.

Nope.
This is a common misconception about semiconductors and it is even
less true in MEMS systems. The low cost relies on the peculiar
economics of semiconductor-like manufacturing processes. Essentially
no matter how complex the device, the cost tends toward the cost of
the raw materials. This is independent of density.

This statement is not, please note, just a matter of looking at price
trends. The people working on these advanced materials and MEMS
devices generally have a very clear idea of what they need to do to
bring the prices down. It's simply a matter of learning and doing it.



"Near diamond"? To what substance, specifically are you referring?

The technical name for the most common form of the stuff is "Diamond
Like Coating". This refers to materials, usually films, which are
composed of diamond without the long range crystaline structure. This
is sometimes called 'amorphous diamond'. Some of the coatings have a
certain percentage of other forms of carbon mixed in, hence the term
'near diamond'. There are a lot of variations on this general theme
and they're being used for a number of things. See

http://www.shahlimar.com/diamond/ for an overview.

For an explanation of the composition, see:
http://www.diamonex.com/abouttech.htm

or in pretty plain English:
http://www.esi-topics.com/fbp/2003/o...Robertson.html

DLC is even being used to coat AIT data storage tape:
http://www.qualstar.com/146103.htm

Notice one DLC maker is even branching out into areas like performance
automobile parts:

http://www.morgancrucible.com/cgi-bi....8257858682609


All I see is arm-waving. How would this fence work? How would it be
adjusted?

Think adaptive optics compared to a conventional telescope mirror. A
conventional mirror works because it is both rigid and precisely
shaped. An adaptive mirror works in almost exactly the opposite
manner. It is flexible and its shape is determined by the network of
actuators behind it. The adaptive mirror is constantly deformed to
produce the desired results as determined by the sensor system.

Well that's fine for optics, but we aren't talking about optics.
The principle is the same however. Higher precision by deforming the
active element under precise control rather than trying to make the
active element rigid.

Now tell
us what, specifically, your tool would do better than existing tools and
how, specifically, it would accomplish it.

At least equivalent accuracy, lower price, increased safety. That will
do for a start.

Adaptive optics is a useful technology because for many purposes a
correction has to be made for variations in air density. It is not a
cheaper way to make telescopes

Huh?
This is incorrect. It is a _much_ cheaper way to make telescopes of
equivalent performance. In fact I'm not sure we could build telescopes
with conventional methods that could match the performance of the big
adaptive instruments.

and in the absence of air it is not a better
way either.

As I noted, it is not cheaper because of the economics of large
astronomical telescopes. The use of adaptive optics in these
instruments has focused on added capabilities rather than reducing the
price of an instrument of the same capability as existing instruments.

Now imagine a fence/table system that works the same way. The sensors
feed back information on the straightness of the cut and many other
things and the fence and table actuators use that information to guide
the wood. (I'm assuming some sort of passive control over feed speed
here. The user pushes the wood through, but the system will either
indicate when it is being fed too quickly or restrict the feed speed.
) Not only does this give you inherently superior control over the
cut, but since it doesn't rely on mass and precision of machining or
casting, it has the potential to be significantly cheaper.

Fine, you have sensors that feed back the information. Now what makes the
adjustment with sufficient force to overcome the forces exerted by the hand
of the operator pushing the piece through?

The tool does. Probably the 'fence' in combination with the cutting
element and some kind of speed control in the table itself. (Think a
variable friction surface leading up to the cutting element.) In the
first instance this provides feedback to the operator. Feed too fast
and this element slows you down by increasing the friction on the
table. Try to overpower that and the machine stops.

Can you make that actuator entirely from your hotshot technology?

The actuator is the element in the control system that causes the
thing to move. It isn't necessarily the whole moving part. So, yes,
you make the actuators entirely this way.

How much will that much silicon cost?
Not much.

How durable will it be? A little piece of silicon properly
supported can be pretty durable, a big piece is quite fragile.

Not if it's properly supported.
The answer is the components be as durable as they need to be.

Again, you seem to be envisioning this thing as being built entirely
out of unprotected silicon. That's silly.

Now, you claim that it "doesn't rely on mass and precision of machining".
Instead it relies the technology you are advocating being able to provide
high forces

What high forces? How high do you think these forces have to be?

for practically no cost.

For the cost equivalent to perhaps half the cost of a good-quality
table saw. Or, to put it another way, about the cost of a Harbor
Freight cheapie.

It does not appear to be the nature
of this technology that it will be able to do that.

Obviously I disagree.



I see. So Celestron doesn't enough benefit in this for small telescopes to
put it in their mass-production consumer telecopes?

Today no. Give it a few years and things might be different.

Or maybe it's because
there's no way to reduce the cost significantly?

Once again, the time confusion.

Much more than hype.

Nope, hype.

And you base this opinion on what, precisely?


There are a lot of proof of principle devices
working in labs, more stuff in advanced development and a few devices
in consumer products, in some cases for more than a decade. The
acellerometer that is the heart of an air bag sensor is a MEMS device.

None of which are tools that are anything like what is needed for
woodworking.

Gee what a surprise. Something that isn't predicted for a few decades
doesn't exist today.

Yes, some woodworking tools might have some MEMs components
someday for some purpose. But using MEMS instead of electromagnetic or
hydraulic actuators to move fences and the like is a huge stretch.

There's a huge difference between 'precision' and 'adjustment'. I
suspect the initial adjustments will be made by hand, or if not by a
cheap screw actuator -- just threaded rod driven by a cheap motor, for
example. That's the 'adjustment'. The precision comes from the
sensor/processor/actuator network handling the fine control once
you're in the neighborhood. That's the precision.


Google MEMS and you'll find a lot of hype. But you'll also find a lot
of very real devices.

None of which do anything like what you are claiming the technology can do.

Time confusion.



Micro devices are tough, by their very nature.

They are? How do you know this?

Well, we can start with the basic laws of physics and what happens
when you scale structures. Or we can go by why I've been told
repeatedly by the researchers and companies working in the field. Or
we can go by their demonstrated performance.

Define "tough". I'm pretty sure that I can, using tools commonly available
in a woodworking shop, break any MEMS device you want to provide me.

I'm pretty sure using nothing more than a big hammer I can break any
tool in a woodworking shop -- unless you consider an anvil a
woodworking tool.


MIT has built micro
turbines for jet engines out of silicon that spin faster and can
handle much higher temperatures that conventional full-size engines.

Oh? What temperature do they "handle"?

You should have read further into the ASME paper you cite. On p 16
there is a chart (table 2) comparing material properties. Conventional
alloys for jet turbines top out at about 1000 C. (This is the
temperature of the material, not the inlet temperature of the turbine,
which can be much higher.) Silicon carbide, which is a long way from
the optimum material, can run at 1500 C by the same measure.

A little further along Fig. 23 compares the performance of alloys and
MEMS-type materials at various temperatures.

Ultimately the material properties determine the device
characteristics (or at least set the outside boundaries). Higher
temperature materials allow higher temperature devices and hence more
thermodynamic efficiency.

Of course even silicon carbide isn't the ultimate for microturbines.
There are a number of materials with better properties we are still
learning how to fabricate using MEMS techologies. The paper mentions
sapphire as an example.

There are other considerations as well, of course. For instance most
turbines have active cooling of some kind. Active cooling for
microturbines is aided by the greater heat transfer that results from
the higher surface to mass ratio. Bearings are a notorious failure
point in gas turbines. Microturbines can use air bearings, which can
be made much more reliable. The list goes on.

Even the early, very (and deliberately) crude microturbine described
in the paper matches the performance of WWII jet engines.

I see. So they provide the same 1980 pounds of thrust as the Junkers Jumo
004?

Strawman. And a rather absurd one at that.

The point is that in the first generation, using wildly unoptimized
design, we get equivalent results in basic design paramters.

I don't think so. They may match the _efficiency_ or the thrust to
weight ratio, but that does not mean that they could be substituted unless
they can match the thrust for a reasonable cost.

Who said anything about subsituting them? Powering aircraft with
microturbines, perhaps. But it's not going to be a subsitution for a
WWII era engine.

And that does not seem likely to happen based on anything that you have described except some pie
in the sky hype about how the price will come down because electronics
prices came down.

There are a lot of people in the field who disagree with you. However
again you're getting sidetracked by your inability to follow the
argument. I offered the microturbines as examples of the toughness,
strength and efficency of MEMS based technologies.

You still don't seem to have an answer for that.

The result is incredible power-to-weight ratios.

According to the guy that developed them
http://www.asme.org/igti/resources/articles/scholar_gt-2003-38866.pdf
the "incredible power to weight ratio" is simply the result of the small
size
and the square-cube law. Scale one to the size of an aircraft engine and
you lose that advantage.

Well Duh! The whole point is that these turbines are small. That's
what gives them their advantages. You use them in groups to get more
power, not make them bigger.

So how many do you need to power a 747?

This is another irrelevancy, but. . .

Depends on how much power each one produces. As a rough estimate
thousands of them.

And what would the engine look like?
Like nothing you've ever seen.

They'd probably be integrated into the structure of the aircraft
rather than hung on the wings in nacelles. It's unlikely the aircraft
would look like a 747, although you could design a craft to match the
performance of a 747.

Understand powering aircraft of any size isn't going to be the initial
application. (Well, okay, maybe some tiny RPVs). Battery replacement
is a much more likely application.


(Want to build a
flying skateboard a la 'Back To The Future 2'? The researchers figured
it would take an array of about 500 of these micro-jet engines, each
less than an inch square.)

Which researchers are those? Where do they say this?

The statement appeared in an article in "Science" several years ago
about MIT's micro turbine program. The researcher who made it was
being facetious, obviously. But the thrust would be there and he was
pointing out that microturbines for larger aero vehicles would be used
in large numbers.

How large would these numbers be, how many square inches of silicon would be
required to make the devices, and how much would that silicon, just the raw
silicon in the appropriate grade cost? And what would happen if one of
these hypothetical engines ate a seagull?

The guy was being facetious, for God's sake! See if you can get your
mind off these irrelevancies and stick to the main issues.

I mentioned it to demonstrate the compactness and power output of
microturbines, not because anyone's going to build one.

--RC


--RC

Charlie Self
"Giving every man a vote has no more made men wise and free than
Christianity has made them good." H. L. Mencken

You can tell a really good idea by the enemies it makes

You can tell a really good idea by the enemies it makes

You can tell a really good idea by the enemies it makes