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Old Apr 21, 2008, 01:48 PM
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Mini-HowTo
Rhino CAD L-plates tutorial

I have been meaning to investigate this package for ages, as the next step beyond 2D CAD. I managed to download a demo for MAC OSX, which is fairly 'beta' if not 'alpha' and mcg promised to be along to assist those wobbly first steps.

I thought a simple project would be to design one of my wooden laminated props. These are intrinsically the sort of thing that 2D cad can do but with a lot of work.

Essentially I plot the cross section of the blade and various points and interpolate curves to define the laminations. It should be possible to set the curves up, loft a surface, and slice it up instead.

So who needs a prop designed?

If the software doesn't expire before I finish, or explode, that will be a new prop in the list of existing designs..

First off is to import a bitmap of a prop to reverse engineer, and decide on diameter and pitch..
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Old Apr 21, 2008, 03:54 PM
mcg
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You may have already seen this tutorial on wing construction in Rhino. If not, it might be useful to scan through it.

http://www.rcgroups.com/forums/showt...ght=rhino+wing

For readers who don't yet know about Vintage's fascinating work with propellors, here is a thread:

http://www.rcgroups.com/forums/showt...59#post6249559

michael
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Old Apr 21, 2008, 04:59 PM
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Well so far its taken me about an hour to get a bit map to trace, and half an hour to unsuccessfully create a sort of ovoid that I cant click or squeeze or reshape in ANY WAY.

With Corel, you click on the node editor, and bodge it into the shape you want.

Now I remember why I hate CAD.

How do I change a simple 2D outline's shape!

ARRGGH

Now I have clicked on something and rotated the whole view..and it wont let me undo it.

I have a horrid suspicion this is the program type where you have to read the small type at the end of chapter 132 of the manual to do the most basic things..

Like 'how to trace a bitmap' and adjust it later.

The complicated things are easy. The simple things are desperately hard it seems.

I cant even show you what I have done as the capture function does nothing!

Well I found something called 'control points on' that allowed me to modify the shape, in a most non-intuitive way, but how to add more control points to an object? How to know where it is located on the co-ordinates? how to place it precisely? how to select and axis and rotate it? how to weld it to something else? The only thing I CAN do so far is a loft..WHY don't they stop adding features and make the thing use less keystrokes?
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Old Apr 21, 2008, 07:17 PM
mcg
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Here are some Getting Started tips about Rhino. I strongly recommend their instructional DVD. It shows onscreen how to use the program.

It might be helpful to start with straight lines and free form lines. I find the "interpolate curve" to be the most useful tool for drawing free form curves. I use it constantly and rarely use anything else. It is an acquired taste, however. Note that you must right click (or press enter) to terminate the curve.

In general, a right click is the same as an Enter keystroke. This little trick adds a lot of speed.

You can double click on the name of the viewport (Top, Front, Side, Perspective) to open up that frame to full screen. Double click again to restore the quadrant of four viewports.

Notice in the first screen capture that I drew the curve on the plane of the Front viewport, but it simultaneously appears in the other three. The control points toggle on and off with F10 and F11, respectively. You can edit the curve by picking and dragging a control point. This sometimes produces bumps. The command, SoftEdit, is a better way. Read about it in the Help section.

Across the bottom of the page are the snaps. Click "osnap" to make these visible.

The "Ortho" command is also down there. It forces straight lines. Toggle it off if you want to draw curves.

In general, the program uses icons to communicate commands. They are not intuitive, but if you hover the cursor over one, a caption will explain what it does.

If you click and hold for a moment any of the icons along the left panel of the screen, a menu will pop out. (You can drag this little menu to the site where you drawing. Sometimes helps.)

In general, I think CAD programs are frustrating because, basically, your fingers have to learn them while your intelligence looks on, helplessly. CAD is a motor skill. Rhino is the third CAD package I tried and the first one I have been able to make real progress with. Bon courage.
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Old Apr 21, 2008, 07:41 PM
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Quote:
Originally Posted by mcg

Here are some Getting Started tips about Rhino. I strongly recommend their instructional DVD. It shows onscreen how to use the program.

It might be helpful to start with straight lines and free form lines. I find the "interpolate curve" to be the most useful tool for drawing free form curves.
Yep.. that seems to be a better tracing means. How to reshape tho?
Quote:
I use it constantly and rarely use anything else. It is an acquired taste, however. Note that you must right click (or press enter) to terminate the curve.
Hmm.. Just clicking on the starting point seems to work..on this version
Quote:

In general, a right click is the same as an Enter keystroke. This little trick adds a lot of speed.
Thats the first good tip..

Quote:
You can double click on the name of the viewport (Top, Front, Side, Perspective) to open up that frame to full screen. Double click again to restore the quadrant of four viewports.
YOU may be able to, Doesn't work here. Looks like they are about 65% only in porting to the Mac. I cant close, or maximise the viewports at all.

Quote:
Across the bottom of the page are the snaps. Click "osnap" to make these visible.
Flyout box here..

Quote:
The "Ortho" command is also down there. It forces straight lines. Toggle it off if you want to draw curves.
Yes..found that one. off by default..

Quote:
In general, the program uses icons to communicate commands. They are not intuitive, but if you hover the cursor over one, a caption will explain what it does.
there are more menus than items, and some of the menus don't work, and at least one command - HandleLine, works, but has no menu item!
Quote:

If you click and hold for a moment any of the icons along the left panel of the screen, a menu will pop out. (You can drag this little menu to the site where you drawing. Sometimes helps.)
Yep I got that far, but there is so much that seems to be missing.

1/. In corel, If I click on an object, I know its size and position co-ordinates, and can edit those and place it exactly where I want. How to do that here?

2/. In Corel, I can have rulers along the edge that tell me whether I am scaled in inches,mm or parsecs. No idea of any of the scales I am using here.

3/. In Corel I can accurately and mathematically scale, stretch mirror and rotate about any point or axis. All done via dialogue boxes. I cant see how on earth to position anything or know where anything is, or what size it is. The only readouts seem to be the cursor but since my hand wobbles that is never the same value twice. And its given in 'units' - no idea what the units actually are...

4/. In Corel I can micro shift and nudge objects to where I want them to be. I see no way to do tis here.

In short the only method I have found of doing anything is with the mouse - surely there must be some way to - say - take a shape, duplicate it, shift it an inch along the Z axis, rotate it 30 degrees and make it 50% bigger in one dimension, and 30% in another?


I know this stuff all has a logic somewhere, but I have to say its all pretty obscure. I am getting the feeling that I have to write a macro or something to get it to do all this..
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Old Apr 21, 2008, 08:04 PM
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Ok..how do I draw something that doesn't vanish?

I can draw a shape with interpolate points, but as soon as I hit the enter key or right click, it disappears?


Oh. things with no surface don't show up in rendered views. Weird mentality these programmers have..
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Old Apr 21, 2008, 08:38 PM
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Here is a screenshot to show how to find the "transform" menu. It includes icons you can use to move, copy, rotate, and mirror. Another useful command of this type is "Orient," which I usually just type. This one moves and, if you want, rescales an object. You pick two reference points on the object, and two target points on the target. I am not sure what you are looking for in terms of dimensions. The screen is gridded, and you can set the dimensions of the grid. But it sounds like you are looking for a literal ruler with a scale.

You might try the DIM command, which will place blueprint-type dimensional and arrows on an object, and call out the exact dimensions in a caption. You can also use this feature to precisely measure and report angles.
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Old Apr 22, 2008, 04:19 AM
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Mmm. Its a definite example of why I like Corel.

If I want to know how big something is, or make it a certain size, the info is there , and I can edit the dimensions and the part follows.

Here I have to dimension it, read it, go through a rescale exercise, and so on. Many more keystrokes. Just to adjust a part size..

Maybe I should just ask you what is the simplest way.

To make a propellor, first off I have a plan view of it to get the blade shape.

Then I decide on an airfoil cross section, and draw that.

Then I have a spreadsheet to tell me the incidence angle or a given radius.

Also, the section thickness needs to increase near the hub..

So, i essence what I need to do is replicate the airfoil section, at different places on the Y axis, each one thicker then the last, each one angled more than the last and each one longer or shorter than the last to match the blade profile.

Then I can loft that lot and slice it and I have my laminations. Those last two parts are what Corel can't do except by me USING it and doing eyeball interpolation. And what RHino does in a second.

The first bit is what Corel does in about 5 minutes, but I cant get Rhino to do at all

So how to I copy and object a certain distance up the Y axis, change its aspect ratio an exact amount, change its size an exact amount, and rotate it an exact amount?

All without the mouse, using typed in numbers?
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Old Apr 22, 2008, 09:28 AM
mcg
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propellor sketch, spreadsheet entry

Here is a link you might find helpful.

http://www.tjpgraphics.com/home.htm

There is a tutorial here on wing construction in Rhino 3D using airfoil data tabulated in a spreadsheet format. The author is apparently coming from the Corel tradition (which I am not) so it will probably make more sense to you than it does to me.

Here is a quick sketch of a propellor. This is one strategy that will illustrate the use of some of the commands.

To make the base of a single rib in the Front Viewport, I first drew a straight polyline from the point (0,0,0) along the axis, with the Ortho on. (Note that at the command line, you are being prompted for coordinates or angles. It you don't enter any, the system will just read your cursor position. This is fine if you have a snap, but I think it is good practice to enter the 0,0,0 at the outset.) I then drew the curve (ortho off) to create a sketch of an airfoil, snapping to the ends of the line.

Second, I unified the drawing of the airfoil using the jigsaw icon. This turns the two pieces of the airfoil into a single unified object, which light up yellow if you click on it.

I then used the copy command (ortho on) to space several copies along the axis (leading edge) and in this way create a "comb" of airfoils. These are of course "dummy" airfoils. In your work you would be using fully defined sections. One way to introduce these is to create a dummy structure, just as a jig, and then replace the individual ribs (or simply marker lines) with real sections, using the Orient command. Orient will simultaneuously insert and scale the rib, so it saves a step.

I then drew the trailing edge in the top viewport.

The problem now is to stretch or shrink the airfoils to fit the space defined by the LE and TE. For this I used the 3D scale command, and snaps, working in the perspective viewport. Basically you give the system the LE point, the existing TE point as a first reference point, and the new (snap) TE point as a second reference point. The system will show you the rib as it stretches and pulls it into the new scale.

Finally, it is necessary to set new angles of attack for each riblike section along the length of the propellor. Use Rotate 2D. The trick here is to "pick" the rib you want to work on in the Perspective viewport. It lights up in yellow when you click on it. (see Screen Capture). But -- essential step -- jump to the Front viewport to apply the rotate command. This way you will rotate in 2D on the surface of the correct plane. The yellow highlight shows you which rib you are working on, against the visual background noise of many other ribs.

At this point, you can surface the collection of ribs with the Loft command. I believe you can then make additional edits to the surface (alter the twist, whatever), but I am a novice at surface edits.

I am sure there are many other ways to do the basic propellor sketch. But the recurring commands for copying, scaling, rotating will probably figure into most of them. To make the dimensions and angle precise, enter them at the prompt. When you are using the same command over and over again, as for example in setting the angles of attack, you can repeat the command simply by right clicking. Saves time.

In boat hull design, the fewer sections (frames) the better. The fewer the sections, the fairer the finished hull. In general, given just a few sections, Rhino can find a sweeter curve than the original yacht designer.
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Old Apr 22, 2008, 05:06 PM
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Forgive me for this! Ha! Ha! (That's because I can draw well with CAD and not even didly with Corel!!)

Seriously now: Correl is a Computer Aided ILLUSTRATION program and CAD stands for Computer Aided DRAFTING. (In spite of the today's use of the word Design.) There is an entirely different bias in the way geometry is described.

Don't even think about paper size until you want to print something. Draw everything in full scale.

I"ve often wished that 'line' type stuff would appear in rendered views too. I think the reason they don't is because rendering is all about surfaces and 'line' stuff has no surface: lines are infinitly thin. In a CAD program, line thickness is primarily about appearance on paper.

Object properties, including size, are all available for editing but not in the same dialogs or menues as Corel. You'll just have to take the time to find them. You'll find a lot of keystrokes used, instead of mouse pointing, because CAD predates graphical user interfaces. AutoCAD was one of the first and has maintained its keystroke heritage: many newer programs have copied the 'style'.

A propeller is a complex object and you may want to learn the program by starting with simpler objects. However, your propeller designs have inspired me to try to do one in 3D, so here's how I'd do it. (I'm sure there are many other ways to do it.)

Set your drawing view to TOP, and draw your desired plan view of the propeller. Draw it in the desired size. It doesn't matter where you draw it: you can and will move it later. You can scale it later to any other size. You should be able to draw it much like you would in Corel. Now ignore it for a while.

Next determine how to draw a 3D helix: A propeller with a zero thickness airfoil is a helictical surface with pitch proportional to radius. Once you get the surface, you can easily add the desired airfoil shape. You should be able to find a command/tool for drawing helixes since it's a basic 3D object type. Practice drawing a helix. I suggest doing it in an isometric view so you can see the shape.

It's futile to attempt to explain farther in text. While I don't use Rhino, I could post some basic drawings to explain the method if you're interested. I'm sure Rhino suports the same basic 3D geometry.

Finally, if you want a 3D program that's easier to understand, try Argon from Ashler-Vellum. It will cost a bit more than Rhino but it has the easiest interface that I've seen. There is also a version for the Mac. You can download a demo version that lasts for 30 days: no other functional limits.

Welcome to the CAD side!

Nick
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Old Apr 22, 2008, 06:22 PM
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many thanks to both of you! Yes,things are becoming clearer. I haven't time today or tomorrow to try this out, but I will.

I was just realising when I mulled it all over that Rhino was essentially a command line program with a pretty face.. It starts with a mathematical description..Corel on the other hand is a computer simulation of a drawing board: everything I had as a draughtsman is there in Corel. Sliding scales, protractors, dividers, french curves..paint brushes, pencil lines where I want them and even colored inks. Even an airbrush..

This of course means a radical rethink in how to do stuff.

I am pondering that actually the propellor problem might well be able to be written as a program of duplicate, resize. shift and rotate followed by a loft and slice..

I haven't time to pursue this for a couple of days, but can you confirm that its possible to execute a series of handwritten commands? I.e. program in Rhino-speak? And save the result as a macro?

This would be ideal for automating a lot of repetitive stuff like tabbing for laser cutting as well.
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Old Apr 22, 2008, 07:58 PM
mcg
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Scripting

Yes, you can program in Rhino's command language. Look up the section on "Scripting" in the Help index, or the Macro commands.

Seems like a good idea to me. It would be a kick to just load the data, and then sit back in your chair and watch the ghostly hand create (and slice) a perfect propellor.

Kind of difficult to stop fiddling around with this wing thing...I added an ellipse and circle, Extruded the circle into a shaft, Capped it, and then ran the Loft again.

Michael
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Old Apr 23, 2008, 12:04 AM
Just Keeping UP
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I first learned about Rhino several years ago when Cathode posted his first design. His CAD drawings were/are so nice that I wanted to try Rhino. I played with the demo a bit back them and let it go.

After my ealier post today, I downloaded the current demo and played with it a bit more. While it was a bit amusing to read of your frustration and its similarity to my frustration with Corel, I must say I apologize completely for my jest. A couple of hours of fiddling reminded me why I quit playing with Rhino before. This program baffles me too! I'm pretty disfunctional with Corel, but this one is completely opaque to me.

I suggest that before you invest too much effort in Rhino, try the Ashler-Vellum 3D programs. They may make more sense to you.

Nick
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Old Apr 24, 2008, 07:31 AM
mcg
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There is a tutorial in .pdf form here, showing the Ashlar interface. Their tool palette is reproduced on page 3.

http://www.ashlar.com/sections/suppo...face_intro.pdf

Their icons do communicate or hint at something about the underlying command. They are not just the typical glyphs.

I notice they use a trackball as an on-screen metaphor.

There is another brief tutorial on drawing fans and turbines, but the pitch looks fixed.

Not sure I see how Argon is fundamentally different from doing 3D in AutoCAD, TurboCAD, or Rhino. Download and try to learn more, I guess.

Their programmers invoke parent-child logic, and they have provided a wonderful command, "hide parent." Surely there is a cartoon in this.
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Old Apr 27, 2008, 11:19 AM
mcg
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Take 2

At a splendid site on wooden propellors I located a clear line drawing showing airfoils and angles of attack for a specific propellor.

http://www.woodenpropeller.com/index.html

The drawing uses geometric contruction to specify the angle of attack as a function of radius. The reasoning behind the technique is explained here by Mike Woodhouse:

http://www.gregorie.org/freeflight/s...ops/index.html

Basically I repeated the Rhino drawing technique outlined in earlier posts, but this time using real airfoils and a real leading edge.

The working sequence is suggested in the captions. The tracing took about 10 minutes; the many, many rotations of the airfoils, in various planes, another 5. Note that if you are repeating a command, you can just right click rather than retyping it. Lofting, editing the A of A settings, and re-lofting, to get the trailing edge to look better, maybe another 7 minutes.

I have been working with Rhino since mid-January. Before that, I took a 6-day course in AutoCAD 2008. Rhino started life as a plug-in for AutoCAD, and the command set is similar. I find Rhino a lot easier than AutoCAD, but without the basic AutoCAD classroom instruction and rudimentary AutoCAD command vocabulary I am not sure I could have gotten very far with it -- or with any other CAD program. As Nick points out, they are all daughters of AutoCAD.

Vintage is right, CAD products are basically program languages. The "pretty face", the icons, are only there to save keystrokes in typing commands. CADing is not drawing. It is programming a computer to display a drawing. The program includes commands and dimensions. When you load a CAD file you are not really loading an image -- you are running a program that re-creates an image step by step.

There are about 10 commands you use over and over (copy move mirror rotate scale orient line etc). But in AutoCAD there must be hundreds of commands, and Rhino also has a very deep command set. This is good. But it is a language. Takes some time.

Here is a prop calculator I came across that (they say) produces files that upload directly to Rhino or Solidworks.

http://jcpropellerdesign.com/

Following is the procedure I used for lofting a prop:
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