burrman

the ter is .000067 meters roughly. i attached some info that may help. the moi model here is in the actual dimensions. probably through all the scaling some confusion arose. the issue bugging michael is that the largest dimension / smallest dimension (radius / ter) is approx. 47619. for a compressor or turbine blade that would be a lot smaller. But even the chord / ter is still 4761.9. Somewhere in there lies the rub I believe. Burrman got it to work so I wanna see if I can too. I like MoI better than rhino because it is simpler to use. I think you have a great program here. I wouldn't change it.

Hi Anthony,

> the ter is .0067 meters roughly.

But that's not the case in the A400M Propeller Example.3dm file that you posted previously.

In that file the little rounded tip here:



Seems to be 0.0000666 meters as you can see... That's 2 orders of magnitude smaller than what you wrote here - is one of these incorrect?

Then of course to actually cut an arc shape on your CNC you will need a precision of some fraction of that, maybe a precision of around 1/1000 of a millimeter or so to cut that accurately...


EDIT: I see you updated with the correct figures above, I didn't see that when I first posted this one.


- Michael

Yeah its really small and if the chord gets smaller like the first points that started this thread it would get even smaller. That's why I switched to this example. The large blend that burrman did at the base is what i was going for. But it would still have to blend into the ter. I used to work for McCauley propeller and Hamilton Standard. We made these types of blades all the time. Even guys with hand grinders could do it. The CNC was just an example. I was trying to say that machines don't make lines or points. There will be some radius based on the drill bit or what not. At P&W we drilled with lasers. Believe me there are a lot of ways to do all sorts of things, that's all I was trying to say. Unfortunately the ratio (radius/ter) that I believe is bugging you I can't change. It comes from the fact that the blade has to have a certain chord. The airfoil spec does the rest. Making the ter larger is an option, but not ideal. I was trying to say it still needs to be a radius for a real perspective and from a stress perspective. So if it becomes too small to manufacture as burrman is saying it would have to be enlarged. I was saying my code just uses the naca spec. Its not like I drew it in there for fun or to bug you guys. I'm ok with making it bigger if need be at this point. But what I sent is the actual definition.

What I can do is change the radius / chord ratio. That will increase the ter and still follow the exact geo. What would be the min ter that MoI can deal with given the same radius of 3.170912 meters?

Hi Anthony, yeah the part that's particularly difficult here is the mix of different proportions within the same surface, since that little radius pushes out with the sweep to a much larger length than that radius in the sweep direction.

That means you've got a surface fragment that is like a long very thin sliver - things like that will cause some particular difficulties, particularly with stuff like join, since with a slivery surface like that both of its long edges may be within tolerance of the other piece you're trying to join it to and it's kind of easy for it to be basically treated as if it was a degenerate collapsed line without any surface area at all.

So anyway, this mix of different proportions within the same surface is particularly difficult - if you had something like a tiny part that was all made up of surfaces that were also of the same proportions that would probably be a lot more feasible.

- Michael

> What would be the min ter that MoI can deal with given
> the same radius of 3.170912 meters?

I'm not sure of the exact value that you'd need, but anything that increases the size of the surfaces that are generated so that they're not so extremely thin and slivery for each surface piece would probably help.

- Michael

I played around in a spreadsheet a bit and changing the r/c wouldn't change the ter that much. It also will drop the efficiency which is bad. It looks like ter is going to be really small no matter what I do. So in the worst case manufacturing scenario they would just have to make it bigger. I've never heard of any issues not being able to meet ter in manufacturing though. It's possible they didn't bring it to our attention, I'm not sure.

Here is just a solid with no fillet applied to the connection of hub and blade... I could get about .001 m before the fillet starts to fold over itself... What were you looking to put in there?

I dont think that anything is really bugging Michael. You will just need to jump through a bunch of hoops to model this. Just like in Rhino. But the point may be, if you are just starting out with MoI, there will be alot of low level work for you (Only more to come) then it may prove difficult for you.

Anything that looks reasonable is fine. I'm just looking for smooth blends that looks like a machine or human would do. So that it can be analyzed later for stress and fatigue.

I'm curious how you set the model up to be able to fillet. That seems to be my biggest problem. I have a bunch of surfaces in the right position but can't get them to fillet. I noticed your model was all one piece and it was able to perform a fillet. Do you have to join them somehow? Being new at this is difficult. But I can clearly see MoI is much nicer than Rhino. I just have to figure it out. I've been at this all day, so I'm tired. I'm going to go to sleep. Thanks again for all the help.

I watched the sunburst tutorial and that's almost exactly what I'm doing, but I just can't seem to get it done.

NACA airfoil equations give a zero radius at the trailing edge (a point). Any radius put there is a manufacturing one and shouldn't affect the performance. I have never seen a propellor with a trailing edge as sharp as a scalpel and would suggest there would be no performance gain even if you could achieve it.

Yes, the model i posted is listed as a "solid" in the properties display. There are a couple different fillets that MoI does... Edge and surface.. The surface one works best when done on a solid object though can create a fillet with seperated surfaces more robustley, but those will also require a lower level of work to get the result into a solid.. It's a good idea to work with solids as that will then have well defined surfaces and structure.

To get your model into a solid form for filleting I first rebuilt the arcs to use in the sweep as I had mentioned before. After I completed the sweep I seperated everything into seperate surfaces and ran a trim on the surfaces of the sweep object and the hub object, using the "keep" option to keep the exterior surfaces I wanted to keep. Then I ran join on all the surfaces and created a solid form that I posted here.

The fillet of that edge will only go so far before it folds over onto itself.. If you put a .25 fillet on that edge, you will see the results on that little trailing edge patch that is created... Note the difference in the 2 verticle patches that run up to it... This is whats causeing the issue for the fillet corner patch area. If it was a sharp, it will be able to make a more well defined patch, but at some value, you would have to look at it and ask "What would I expect to see put there???" A proper patch structure cant really twist in and around on itself to satisfy the area...

"""" I noticed your model was all one piece and it was able to perform a fillet. Do you have to join them somehow? Being new at this is difficult.""""

It's not really going to be anything you find in the manual for doing what we are talking about here, but those 3 videos Michael has there, cover things pretty well. Even Rhino wont be having specific direction on working in the manner you are describing. Even the higher end stuff may have a need for understanding whats happening under the hood to have success!

Maybe Danny, who is a user here, can find the time to look at your file with NX, a very expensive modeler using one of the more powerful modeling kernels, and comment on the type of results it produces with simple "boolean and fillet" with no need to jump through hoops...

Bueller??? Bueller????

As an example, I created your model as 2 solids "pre-boolean" and sent it to a program that uses the parasolids modeling kernel. Powershape.. Importing the parts in it first starts me through a process of setting up "tolerances" that I want it to use on the part.. Something like a 6 step process.. Then I booleaned the 2 parts together and it started an automated wizard for setting up the tolerances for gap allowance/disallowance and stitching of the surface to ensure a water tight solid.. I then ran a fillet on the edges we are discussing here.. It ran the same size as the MoI file I presented and also created the exact same twisted patch with the larger radius!!! (Than really fits with that geometry)





The red is the underside of the corner patch rolling over onto itself and folding upwards..

At this point, there will be some complicated "Help me fix this area" tools, asking questions that I need to know the answer to, to try and create something there..The help me tools may not exist for the issue and then I will need to know what to do. It may be a week long process to finish just this one component of the model. Then, the very next issue starts all over again... Maybe a months work or more???

Anyway.

@ Bur: Have you the free Version of PowerSHAPE?

Thanks burrman,

I will keep at it. I'll try to do what you did. Did you have to scale the model at all. Or did you just increase the ter. At this point, I'm fine with increasing the ter. It could be that it was increased by the manufacturing department and I just didn't know about it. Everyone keeps focusing on that point, rather than the bigger issue of just getting the model built in MoI. If the ter has to go up then it has to go up, I don't really care at this point. All I have been saying is that is literally the definition from NACA. It is not zero as people have been trying to say. I already attached the document I referenced to write my code (ter = .00021 * chord for the NACA 65A009). You can not bring a zero ter down to a hub and have a working propeller, it will crack instantly under extreme centrifugal forces. Usually the blades are blended from an airfoil to a circle for a variable pitch blade. I'm trying to do a fixed pitch blade so it will blend to something but what I'm not entirely sure (however, burrman is nailing it, exactly what I'm going for). Again, I just want something that is reasonable that either a guy with a grinder made or came off a cnc machine and then was cleaned up by a guy with a grinder. If the naca def is too small, which it may be, then it will obviously have to go up some. But it can't go up that much or the chord will shrink and change the performance. So its still going to have to be a rather small ter blending in to the hub. Again, the idea is that the model would go on for further analysis such as fea. So a realistic model of the blend is my goal.

I've literally never used MoI before, so your patience is appreciated. I spent all day yesterday with it and found it a lot nicer than Rhino, which I have used occasionally. I never could blend the blade into the hub in rhino. It sounds like once I learn what burrman is doing in MoI it probably will explain my failure in rhino. But from what I can tell here MoI works a lot nicer, so I would like to figure it out. Probably all I need to do is learn how to build the airfoil profile better so it sweeps right and then it will work better. Then of course learn how to join it all together to blend it. All of which burrman is trying to explain to me. I'll keep reading, watching tutorials and practicing because it seems like its worth learning and using MoI over Rhino.

The only things I can say from a new users perspective is that the pan and rotate buttons in screen aren't what I would expect. I would think you click the button and then the main action would be those. Not click and hold and move on them. Also when an op fails no output is given. It would be nice if it said the op failed like rhino. Other than that, I think its pretty darn awesome compared to Rhino.

Anthony

p.s. burrman please don't spend two months or more on this. you've done so much already. you have shown moi can do what i wan't and this is just a newbs inability to operate it properly. i won't be here much of the day, so I'll get back at it tonight and tomorrow.

""""" Have you the free Version of PowerSHAPE?"""""""

Hi Frenchy,
Yes.. It's nice as it allows the use of the entire tool suite. If I needed to do work in it and actually save the files, they have an option where you can save a file for $99.00.

Hi prop,
I didnt change anything in the file you posted (Actually, it didnt have the center hub in it, so i copied it from one of the other files and had to scale it to fit.. Maybe you should check it's dims) The only thing I did was rebuild the ler and ter arcs so they were a single segment instead of a broken arc. Same dims though.

We understand that there is a ter radius defined there.. The problem is to model such a miniscule number (miniscule in relation to the rest of the models numbers) is going to present you with very low level problems that need to be addressed. Michael has already stated that MoI "Could" do it, but it is not setup as the tool to deal with what you will be facing with this situation.. I could do the fillet in Rhino too.. His suggestion was, if you really have the need to put that tiny little value into the mix, you may need a more specialized software to accomplish the model.. Or, essentially he will be building it for you over the next month. Every next move will require low level understanding and manipulation (Not in the manuals).

As you point out, many of those blade features are something done by a human, not a machine. I pointed out some info on the naca specs where they actually change the numbers to zero for computational work. If you have a need to model it specifically as-is, for FEA, then it will not be something you wip up in a day or 2.

"""""""""burrman please don't spend two months or more on this. you've done so much already. you have shown moi can do what i wan't and this is just a newbs inability to operate it properly.""""""

Well, not really. It's more like you will run into this with "Any" of the software you attempt this with. The understanding of whats being said about the difference in values with relation to each other, is the key.

"""""""The only things I can say from a new users perspective is that the pan and rotate buttons in screen aren't what I would expect. I would think you click the button and then the main action would be those. Not click and hold and move on them.""""""""

A right clcik/drag in the viewport will pan the 2d ones and rotate the 3d view. Middle click will pan the 3d view..Shift riight clcik will pan the 3d viewport and cntl right clcik will zoom all of them. The viewport buttons are adjustable in the options dialogue. You can make them sensative or not (Like for using them when zoomed way in on something very small.) Their rates are adjustable.. I think they were also designed with a tablet user in mind.. People who use pens to work the computer.

hi,

I played around some in moi and rhino and even rebuilding the arcs and making a solid I still had issues. I thought of a different geometry that should fix everything. when I get it done I'll post it. ill try taking off the ter and with the different hub geo I have in mind it should work out.

Michael,

Here is the model you requested regarding trim not working. It is the same model as before. I just saved it at the point of the trim. The work around I have been doing is just deleting the circle and adding an arc. But if you try to trim the circle, using the two points that lie on the circle, nothing happens. At least for me.

Thanks,

Anthony

Edit; Attachment has been removed to save space on the server.

Hi Anthony, thanks for posting the circle trimming file.

The problem there is again related to the small numeric scale of the objects - your circle there has a radius of 0.0018 and that is too close to the default tolerance level of 0.001 units.

You can solve this by going to Options > General and switching your units to millimeters instead of meters. After you do that your circle will have a radius of 1.8 units instead of such a small numeric value, and then the trim will work fine after that, see the attached example file.

Like I mentioned before, you'll likely run into a variety of problems trying to work with objects that have such a small numeric size - try working with your objects at a larger scale (but don't go overboard into the millions of units though! - think more along the lines of 10 units or so) and things should generally work better.

I'll see about tuning up the Trim command for v3 to use the relative tolerance mechanism which should then make your original example work. The relative tolerance system uses a tolerance that is calculated as a fraction of the object's bounding size so it adapts itself to smaller objects and that works better in situations like this.

- Michael

Hi Michael,

Yes I am starting to really understand your .001 tolerance based on the bounding box. I tried all sorts of ter variations. A point like some suggested, a line as others suggested. Even larger radii. I found, like you said originally, that I would spin my wheels based on the tolerance issue. So I drew a bounding box for the airfoil and worked with that. It went a lot better. All functions worked. I did still have to change the mesh angle from 10 to 1 degree so that it looked smooth on my laptop. But it didn't seem to slow it down any. I created new geometry that may help you or whoever is interested experiment. It is setup to easily apply real life fillets at the base. The blade would need the airfoil ground out as well. So the model is much like you would see in a forging. Prior to being machined. Given the issues we spoke of, this is about as far as I can go with it. But I'm happy with this representation. Its good enough for now. I really enjoyed working with MoI over Rhino, PowerShape, and Autodesk 123D. The forum support was fantastic as well. I have never been a fan of CAD, I am primarily a FEA guy. I have found CAD work to be absolutely no fun. That is until I discovered MoI. I really enjoy firing it up and using it. In fact the more I use it the more a feeling of dread comes over me when I go back to Rhino. MoI is so easy to use. I love the fact that there aren't a lot of different ways to do the same thing. One way for one thing is a great idea to me. The UI is hands down the best I have ever seen. Icons that you can read and know what they mean. I think if you implement the adaptive tolerancing in the future it will really make MoI stand out even more than it already does. I'm going to continue to learn MoI as it definitely seems worthwhile.

One thing I learned through this trial was that Rhino wasn't doing as good as I thought. While I could jack up the tolerance (1e-6 meters) so that I could generate the blade. It still would not make solids from those surfaces and it would not fillet anything. I never realized it was having a problem with the geometry because I was able to work with it. I would much rather have what MoI was doing. Point out the problem right away. Rather than make me think things are ok, when in fact they are not.

The process right now would be to use PROP_DESIGN to generate the blade geo (airfoil profile and rails), model it as much as possible in MoI, and take it to SolidWorks to finish it out and do FEA. I never mentioned this as it was a little off topic, but it may answer a lot of the why am I doing this questions. The geo you see is the ideal shape. Under load it will deform a lot. So I have to generate new rails and iterate to determine the manufactured shape. So you have to go through this process a lot. Therefore ease of use is imperative. There is a lot of iteration required to determine what the real manufactured shape needs to be in order to yield the required shape for aerodynamic performance. Not to mention having to resize everything so it can withstand the extreme stresses. So this is not a one time through CAD and your done deal. For any given model, you will go through this process many many times over.

Sincerely,

Anthony Falzone