CAD Tool For Design Tiny Aircraft

Creating a 3D parametric model can be likened to programming. Some
people make spaghetti code and some make nice tight robust models.
This is called capturing design intent.

It can also be likened to a database capturing spatial information.

You can iterate in a non-parametric world too. It takes good revision
control.

TOP

"Le Chaud Lapin" wrote in message
ps.com...
On Sep 27, 6:16 pm, Dana M. Hague
d(dash)m(dash)hague(at)comcast(dot)net wrote:
A fully 3D program is, IMHO, a must for any kind of design, anything
else is silly. A parametric modeler, however (like SWX and many
others) can be very cumbersome to use... and I've used a lot of them
over the years. Yes, if the design constraints are set up correctly
from the start, minor changes can be ridiculously easy... but if not,
or if you don't have a clear idea of where you're going from the
start, you can find yourself boxed into a corner and have to start
from scratch.

Personally, I prefer a pure geometry based modeler. Simple
dimensional changes affecting many components may take longer, but
it's far easier to make large sweeping changes if necessary, or switch
to an alternate design approach. Most of my work nowadays is large
machine design (though my degree is in aero engineering), for which I
use KeyCreator (formerly Cadkey). Same price range as SWX, though,
which I don't define as "cheap".

I read all the responses and looked around the 'Net, and it seems that
SolidWorks, if not what I'm looking for, is create by people who had
the mindset I was looking for.

But now I am confused. I thought parametric modeling was good.

I program computers from time to time, and being able to change the
structure of a component and have everything that depends upon it
change accordingly is simply invaluable, so I cannot see why this
would be bad. That's precisely the behavior I want.

For example, in my miniature aircraft I envision, there is only one
fuel tank, and it's cylindrical, but its radius and length are a
function of several other parameters.

I am guessing that, like in programming, there is an art to
structuring the interdependencies so as to minimize likelihood of
running into dead-end that you mention.

Finally, I was really surprised to learn that parametric modeling was
not fundamental in all CAD programs. I cannot imagine what it would
be like to try to optimize a design without it. What do people do
without parametric modeling? Tweak every single component manually
during optimization phase?

[I am going to give Alibre a look also.]

-Le Chaud Lapin-

Don't let idiots like jon banquer confuse you. Solidworks, ProE, Inventor,
UG, CATIA, Alibre, SolidEdge and some others would all work fine for what
you want to do. It mostly depends on your budget, your suppliers/customers,
your pool of potential designers/drafters, level of support required, and
maybe corporate culture.

On Sep 30, 9:40 pm, jon_banquer wrote:
Suggest you find your way ASAP towww.kubotekusa.comand view their
video on direct dimension editing to see what can be done without
parametrics.

Ok, I just watched the video, and I barely understand anything, as I
am an ignoramus when it comes to CAD. However, it seems that the "dumb
geometry", as the presenter calls it, allows "dumb dimension-based
editing", but after you are done fiddling with "witness lines, etc.",
you have your model, and nothing else.

Parametric modeling, OTOH, as I understand it, allows the programmer
to define constraints, and let those constraints rest in a sack that
is carried around with the model. If that is the case, I *absolutely
love* this feature! The power of this approach should be apparent, I
think, no?

Now I think I see what TOP meant in his response to your post, about
spaghetti code. I think the preference for the models depends on the
approach to designing systems. Some people think in terms of
relatives. Some think in terms of absolutes. I think in terms of
absolutes. I'd rather walk around in woods for 2 or 3 days working out
the kinks of a system in my head before I commit to anything, even if
I think I already have 40% of the answer. Only when I am sure that
the remaining irregularities are so minor that they will not impede
the march toward finalization of the design will I commit. Then I
employ the tool bear down upon my preconception of the system to see
that it is correct and to optimize it. I guess this is why I prefer
parametric. It seems like it is the right tool for the tightening
process during optimization.

Incidentally, that is the whole reason I've decided to fiddle with CAD
to make minitature plane, to see how much cost reduction can be
achieved by rethinking the system as a whole and not simply trying to
get better prices on conventional components.

-Le Chaud Lapin-

Ok, I just watched the video, and I barely understand anything, as I
am an ignoramus when it comes to CAD. However, it seems that the "dumb
geometry", as the presenter calls it, allows "dumb dimension-based
editing", but after you are done fiddling with "witness lines, etc.",
you have your model, and nothing else.

It's very important to understand that parametric data does not get
exchanged
between different cad systems. What you get is a "dumb solid" when you
open
your model done in Solidworks in another system like SolidEdge. All
the design
intent / parametrics you established in SolidWorks will be gone.

Now I think I see what TOP meant in his response to your post, about
spaghetti code.

His example is one sided and doesn't give you the downside of
parametric
modeling.

http://management.cadalyst.com/cadma...ID=1&sk=&date=

"KeyCreator is a nonparametric application, but that isn't necessarily
bad. It gives users the freedom to do all kinds of things to a model
that they'd never think of doing in a history-based system."

I use SolidWorks everyday. I don't use KeyCreator. I'm not foolish
enough to think that a parametric / history based approach to modeling
is the only approach or always the right approach and unlike most
others in the SolidWorks newsgroup I'm not a product loyalist. Dana
Hague had some very valid points in his post to you.


Jon Banquer
San Diego, CA
http://worldcadaccess.typepad.com/bl...mment-76366100

On Oct 1, 9:15 am, Dale Dunn wrote:
Le Chaud Lapin wrote oups.com:
I have built and flown some radio controlled model airplanes, and I think
SW could handle modeling something of that complexity fairly easily, if
the models are structured well. If not, it will be a painful experience.
Having said that, even with a well-structured model, there will be
frustration with rebuild errors and the like. Hopefully, R/C airplanes
are similar enough in scope to your project that my opinions will be
useful in your decision.

Ooooh...rebuild. I like rebuild. I guess it's the same concept of
compilation in programming. I was wondering in my OP if there were an
equivalent with parametric models. After all, with all the
interdependencies..something has to be synthesized from the expression
of interdependencies, just like in programming.

This is my first design of anything using more than a ruler and scraps
of paper, let alone an airplane. I know it will take years, so I'm
going to just take my time and learn what I need to know as I go.

-Le Chaud Lapin-

On Sep 30, 10:40 pm, TOP wrote:
Creating a 3D parametric model can be likened to programming. Some
people make spaghetti code and some make nice tight robust models.
This is called capturing design intent.

I think I get it now. Hit me while walking my dog.

Example:

1. One dimension of fuel tank depends on required fuel capacity.
2. Fuel capacity depends on mass of certain parts.
3. Mass of parts depend on geometry and density of material of those
parts and load requirements, etc..
4. Load requirements depend on configuration of other structures.

And it would seem that there is a right way and a wrong way, and
again, finding the right way is more art than science. "Reaching" too
deep into model to extract parameters to be used elsewhere might be a
bad idea. Deliberate indirection and hierarchy would be important.
There would also be opportunity for circular references. Also, there
should be some kind of "on/off, part is there, part is not there"
programmability.

You can iterate in a non-parametric world too. It takes good revision
control.

I was wondering about this. It seems like parametric is a superset of
non-parametric in some ways.

-Le Chaud Lapin-

This isn't quite aircraft, but a while back I wrote a VB macro that,
in conjunction with a very crude model of a concrete mixer, was
capable of predicting the CG of aforesaid truck with a fraction of an
inch of what the customer was measuring. For such studies you make a
rude and crude model that will update quickly but that captures the
intent of the study you are doing.

I will many times not even use a 3D model if I can do it in Excel.
Nobody likes this because you can't see the pretty pictures, but you
can run through lots of scenarios very quickly that way. And with the
solver in Excel being what it is there is little that can't be done to
get close to the right answer.

TOP

PS Also search the NG for configurator. There are some very good ones
out there for SW.

Your walk in the woods method is something that I run into every day.
Unless you have a very special mind, spatial relationships are very
difficult to imagine and solve mentally. You can get the topology in
your head, but when it comes to parts bumping into each other in 3D,
most heads can't get around it. 3D CAD brings you down to reality in a
way that even 2D CAD cannot do because in many ways 2D CAD is still a
mental excercise (Thank you Gaspard Monges). Frequently you will
encounter people with ideas that don't stand the test of 3D. This
isn't just an associate with a quick scribble on an envelope, but even
many 2D drawings are simply cartoons. What 3D CAD is, is a way to
simulate reality realistically (well up to a point). There is a
continuum:

1. 2D CAD (catches and idea, still much is required in the head)
2. 3D CAD (captures the 3D constraints, will it fit, etc.)
3. Kinematics software (will it move the way I intend, what are the
rigid body forces)
4. FEA/CFD (How will it deform, How will air flow over it?)

The first is probably the quickest route to getting a specific idea on
paper. The next one is more flexible and more time consuming. The
third requires the work of the second plus additional work and the
last also requires the second and perhaps output from the third to
give good answers.

Since SW starts with 2D sketches for the most part it captures much of
1 and pretty much all of 2.

TOP

On Oct 1, 2:18 pm, Dale Dunn wrote:
Anyhow, parametric CAD seems to be the tool you need, and you will grasp
the mechaniics of using it very quickly. A good coder should easily,
almost intuitively grasp what it is to organize the models well. I think
you will be ok, but there will be bumps along the road (such as managing
strange dependency behavior). SW will serve for your task, but something
like Alibre may be sufficient and much cheaper. Demo versions of most CAD
packages can be had, and standard advice is not to pay any cash until you
have taken several for a test drive.

I think I will try Alibre. I was sure SW was what I wanted, but
Alibre looks good from website too.

I've been to the SW website about 5 times today hoping that, by magic,
the price would drop to $100 for full version. Strangely, this has not
happened, so I need get an eval version soon.

-Le Chaud Lapin-

"Le Chaud Lapin" wrote in message
ups.com...
1. One dimension of fuel tank depends on required fuel capacity.
2. Fuel capacity depends on mass of certain parts.
3. Mass of parts depend on geometry and density of material of those
parts and load requirements, etc..
4. Load requirements depend on configuration of other structures.

And it would seem that there is a right way and a wrong way, and
again, finding the right way is more art than science. "Reaching" too
deep into model to extract parameters to be used elsewhere might be a
bad idea. Deliberate indirection and hierarchy would be important.
There would also be opportunity for circular references.

This is going to be very tricky. There HAVE to be circular references in
your optimization. When you change the weight of the fuel tank, you have to
reevaluate the size and weight of all of your other components to account
for the new load. But now you have changed the weight of the rest of the
components, so the fuel tank needs to change again. If you are lucky, the
solution converges and you end up with a design that works. If you start
from the wrong spot, it might never converge.

The good news is that you seem to have the type of mind set that would allow
you to work through this type of problem. The bad news is that it is an
extremely complex problem that requires a lot of deep knowledge in many
areas of design.

Jerry Steiger