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CAD Software- Tools for designing models

John M. Carron provides a primer on Computer Aided Design for modelers.

The following is information that I would like to share with my fellow modelers. I am excited about what can be done, how it is done, and by the fun and enjoyment one can experience in modifying or creating a "model" drawing using the computer. For those older modelers, do not shy away. If I can do it, so can you. I am 50 years old, an analytical chemist (GC/MS) by trade, and have taught myself some of the basics for using a personal computer (PC).

There are several ways to get model plans: buy them, borrow them, have someone else draw them up for you, or make them yourself. Wouldn't it be nice to exchange your plans with your fellow modelers? Your friend has drawings for a 1/4 scale "Fairchild Super 71", but you don't want a 14 ft. model. You want one with about 50 inches wing span. If you have the drawing in an electronic format that can be read by a computer program, then life can become a little easier. At least you will have a good place to start.

 

Enlarging a Drawing

Most of us have used a photocopy machine to copy and enlarge a small model plan, a part, or a 3-view so that we could trace it out and make a drawing from this enlargement. Randy Randolf (MAN, April, 1996, p14 in "How to:") has shown us how he uses a hand scanner and a word processing program that includes graphics. He demonstrates 6 steps that he uses to scan (copy) a small 3 -view, then enlarge it. With his technique he is limited to making an enlargement of only 1 page in size, at a time. Using the same technique of copying a 3-view, a much larger drawing ( up to 9 feet, using 100 sheets of paper !) can be made using a Poster program from Bob Bedoll ( email BobBedoll(at)aol.com, or postersw(at)aol.com).

Poster is a shareware program for making posters, as in larger drawings, bigger than one page, even full size plans. Take your bitmap drawing (*.bmp file) or windows metafiles (*.wmf file) and enlarge the drawing as much as you want. Then use your printer to panel the pages together. The result will be of similar quality to one that would be obtainable using a photocopy machine. An example application might be the blow up/enlargement of a small 3 view found in a magazine article ( as in the above by Randy). Remember, a blow up only magnifies what is already there- it adds no extra detail.

You will find that an image is actually made up of a lot of little dots.  These types of images are called "raster images."  The bigger we blow them up, the bigger the fine lines become, until they are jagged and a lot wider!  To get a sharp image you must reproduce the drawing in a "vector" format, the format commonly used by CAD programs. A drawing in a vector format that has a line, for example, at 0.1 mm, even when enlarged 100 times, will still have that same line remain at 0.1 mm, not 0.1 x 100 = 10 mm, as would be the case if a photo copier was used over and over again.

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Fig 1.  Original image looks the same in both vector and raster format

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Fig 2.  Raster image becomes jagged when enlarge

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Fig 3.  Vector image is defined only by the endpoints of the shapes contained in the image.  Therefore, it can be enlarged without becoming jagged.

Unfortunately, there is no easy method to translate a drawing from raster to vector formats.  Some sort of manual work must be performed.

 

Converting a Raster Drawing to a Vector Plot (CAD)

Using a CAD program to TRACE over our little picture allows us to essentially take what was a raster or bitmap drawing and convert it into a vector-based drawing. This vector or line, has a starting location and a distance and angle to another location or end point. Curves and circles are calculated mathematically from defined reference points. Hence, the drawing can be made to any size (within limits, suitable for our purpose) and the tracing will remain sharp.

Jim Ryan (It Starts with a 3-View, MAN, p92, Dec.97) describes how to get a 3 view into cad, or you can use a program called Scanover to get a factory 3-view drawing (raster or *.bmp file) into ModelCAD so you can trace it over into a vector format.  Another CAD program, Drawing Board, is available for a free 30 day evaluation. It can be downloaded from the net (sales(at)mcesoft.com). Drawing Board has a feature that allows the importing of raster files that can then be traced over. More recently other cad software programs have come on the market that include not only a "scanover" type program that allows the bitmap file to be loaded and then traced over, putting it into a vector format, but to also be automatically converted or autotraced into a vector format. DesignCAD 97 and Turbocad V4.0 support this feature. ViaGrafix (formerly American Small Business Computers Inc.), the makers and suppliers of ModelCAD, are now offering The Complete Design Solution.  This has both the 2D and 3D version 8 and Scan PRO (automatically converts scanned bitmap files into CAD vector files) programs. These are all and more than you'll probably ever need!

With these programs and a scanner, you can copy any drawing and make it to any size on your printer. For those not familiar with a scanner, think of it like a photocopier or fax machine that gives you an electronic image that can be saved in a file. The file drawings can be edited, scaled, or whatever you want to do.

One excellent feature in DesignCad 2D allows a bitmap to be loaded and printed to any size without doing any other work on the image. DesignCad 2D also allows you to trace over an image (to draw it into a vector format) similar to what ModelCad and Scanover did as a package only DesignCad 2D does a lot more for the same money. If you feel that you just want to enlarge the plans without tracing them over, then you can load the bitmap drawing into a file and enlarge it to whatever scale you want, make changes, then print it out full size using the paneling mode as could be done using the Poster program.

DesignCad 2D allows you to zoom to any size when making a tracing, as does Drawing Board. This has got to be the easiest way to do this, unless of course you want to use ScanPro (raster-to-vector conversion program) which will do the tracing of the raster (bitmap) drawing into a vector format (CAD) drawing automatically.

With ScanPro, the 3 view line art is scaned and saved as a .TIF bitmap file. This file is then used in ScanPro which has settings to include or enhance circles, curves, spacing between the raster dots, and thinning of lines.The file is then saved as a vector drawing which can be loaded into your favorite CAD program. This drawing will require a "little" cleanup and removal of unwanted lines, and text information. I found that for making just an outline of a model with its basic shapes, the following method worked great: First I loaded in the 3 view drawing. Then, I removed any material that I did not want. I then adjusted the wings such that they went through the X axis with no rotation.  The fuselage top view was set vertically on the Y axis, with a center line drawn from the spinner down through the rudder fin and out the back. Next, these drawings are selected and the lines were changed to a series of widely spaced dots. A tracing was made of only the outlines wanted, using a solid line set at .01 inch. The final result was an outline using a solid line, and the remaining detail on the diagram shown only with finely dotted lines.Only one half of the fuselage and wing were done this way. These outlines were then mirrored to produce the other symmetrical half. A little trial and error will get as little, or as much information on the drawing as is required.

Of course if you really want to get serious about your vector drawings, Kreon Industries offers a contactless 3-D Digitization that can take any model or object, and do what is called a laser plane projection by the sensor which sweeps the surface of the component at the rate of 600 to 15,000 points per second, down to a resolution of 10 microns. This information is adapable to most CNC, CMM or special machines and is compatible with most CAD/CAM software. You could probably take a small "plastic 1/72" model and copy it, then make up 3-D plans, or have a machine duplicate the model in another size ! This is way out of my league, but it is available .

For those modelers that want to get started on a scale project using 3 views, the Paul Matt 3-View Scale Drawings are coming out on a CD in TIFF and PCX format

 

Using the CAD Software

To really appreciate how computers can help you design a model, consider a tapered wing where all the ribs are different. You only have to draw (or enter in the rib co-ordinants , perhaps from Dr. Michael Selig) the root rib at 100 % size (if you have ModelCAD, you will have a library of airfoils from which to choose). Now that we have the rib we can make it to any size and it will be to exact scale, whether it is 5 inches long or 25 inches long. Copy the rib and block (paste) it into the area where you want it. The CAD program will draw the exact rib size to fit between the points you want (leading and trailing edge). Alternatively you can note the size of the required other ribs. If the next rib required is only 87% as long, then zoom the copy size to 0.87 and enter. Presto! An exact rib at 87% size.

If you wanted to change the rib size in height (y axis) only, you could multiply (scale) the vertical y component. If we wanted our rib to be 10% thicker, we would multiply the y scale by 1.1. This may sound confusing here, but really it is not. When you are doing your work and drawing, a little trial and error will quickly show you just how easy all this is.

db_lt.jpg (34330 bytes)
A sample screen from Drawing Board LT.  The rib of this fun fly plane can be thickened or thinned easily depending on the desires of the designer.

ViaGrafix, who makes ModelCAD, also make Wingmaster, a program that prints NACA 4,5, and 6 digit series airfoils, in addition to a library of 300! The CAD program will allow you to draw parallel lines , whether they are straight or curved as required. You can space these parallel lines to match the thickness of the sheeting being used. If you find that you like this technique and are having fun, then you can always upgrade or buy a bigger program when you have exhausted the capabilities of the program you are using, in this case ModelCAD.

To scale up ( or down) a drawing to a particlar size is as simple as clicking on the dimension of the model's wing span and typing in the wing span you want. All the other drawing dimensions and measurements are automatically corrected and changed to this new scale size. Yes, it's as easy as that! If my model has a 47 inch wing span and I want to make a model with a 63 inch wing span, call up the units option, click a point on the left wing tip, and a point on the right wing tip, and type in 63. That's it! The model is now scaled for a 63 inch wing span.

A few of my fellow modelers aren't interested in this new technology, or feel that it's not worth the effort to learn. Judging by the high level of their modeling ability, they would have no trouble at all handling a CAD program run on a PC. After all, aren't all the new transmitters programable? If you can master these, you can master a drawing program.

When the urge strikes, a lot of us just like to get out the pencil and paper and start drawing. I guess that this is probably the quickest way to get started. With ModelCAD there is a calculation sheet called ModelCalc. You enter in data such as fuselage length, nose length, wing trailing edge to stab leading edge, wing span, cord, sweep,stab chord,sweep,stab span, stab cord, fin height and fin cord, etc. The program then calculates wing area, C of G, wing loading, etc. even throwing in a comment about whether the model is reasonably well designed or not. In addition to this, you can make a 3-view print out which gives a basic model drawing with all the correct moments, lengths, and sizes. This drawing is similar to a flat sided model, it lacks the curves and fine detail, at this stage. You can add details such as the curved wing tips, a large spinner, bubble canopy, turtle deck, or whatever else you want. You get a basic 3-view outline with correct dimensions, on which you can build the details.

Hopefully you now have an understanding of the basics of operating a CAD program.

 

Recent Articles

Lucky for us, many of the major modeling magazines have been publishing articles about CAD software. Unfortunately, the industry is moving so fast it's hard to keep up. What was available a year ago is fine, but what is available now is even better, bigger, faster, and cheaper!  Still, I thought it would be helpful if I referenced a few articles for those who are interested in further study:

  • A quick review of Col. Art Johnson's articles in R/C Modeler Magazine: Dot Matrix Plotter, Jan./1992 Scan Over and Design Cad 2-D version 6.0 , Aug/1992 Wing Design and Edit Foil , Jan./1993
  • Dave Garwood, Survey of Programs for Modelers, MAN, p46, Jan./1995
  • Roy L. Clough Jr.'s reviews Cad for Your Model Planes, MAN, June/1992 Design Cad 2D version 6.0, MAN, p38, Oct./1995 WingMaster, FM, p32, Mar./1997
  • Bill Griggs, R/C Cybernews, Scanover and Aerodraw, MAN, p108, Mar./1997
  • Jim Ryan, R/C Cybernews, CAD Drawing: It Starts with a 3-View, MAN, p92, Dec./97 (Jim is doing a series of articles, which may be the best yet!)

 

Sources of information:

 

I hope that this information may be of some help to those that are interested in making their own drawings. The advantage of having your drawing in ModelCAD, or a vector format is that you may share it with your fellow modelers. Wouldn't it be nice to exchange plans, perhaps improve upon them and share the fun ?

John M. Carron
johnav8r(at)networx.on.ca

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Old Sep 27, 2008, 06:54 PM
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