Hi Anthony, I'm sorry but I'm not sure what you mean by "MoI won't sweep an arc or radii" - could you please post a 3DM model file that has the arc in it that you're trying to sweep so I can see what you're trying to do?

- Michael

I'll have to install the 30day trial. I had installed the no save version. It is hard to explain. I have an airfoil. I import the points and then make curves from the points. The leading and trailing edges are made with arcs. When I try to do a two rail sweep it won't sweep the arcs. Its ok with the splines. Give me awhile to install the other version and make a file that may help to clear it up some.

On a side note I'm having trouble with the trim. It doesn't seem to work for me. I found a work around, but just wondering why I can't get it to work.

Hi Anthony,

> It doesn't seem to work for me. I found a work around, but
> just wondering why I can't get it to work.

Well, there are a number of possible reasons - like for example if the cutting object does not intersect the thing you're trying to trim it won't produce any result. Or if you have a curve that intersects a surface it must cut the surface into 2 complete pieces you can't trim with a cutting curve that looks like this for example:



It's pretty much impossible for me to know what particular problem you might be running into without actually seeing the model file that you're working with.

- Michael

Thanks,

I have a circle I'm trying to trim with two points. Here is the file you requested regarding the other issue. This works in rhino. If you select one side of the airfoil curve and do a two rail sweep MoI won't sweep the arcs, just the spline. I have tried a few different things but I can't get it to sweep the leading and trailing edges of the airfoil. You have to zoom in a lot to see the trailing edge, its very small. I have it set up exactly like rhino has to have it. I had to fight a lot with rhino to figure out what it needed. I'm fine with having to do it a different way, but I made the file to make it as easy as possible for you to see what I mean.

Anthony

Edit; Attachments have been removed.

Is this the shape you wanted??

Join these 2 edges then sweep the 2 rails:

If you select one arsc the sweep 2 rails works
If you select the other arc the sweep 2 rails works

If you join the 2 arcs the sweep 2 Rail works

If you select the 2 arcs (not joined) the Sweep 2 rails don't works
(posted in the same time :)

hi,

yes that is the shape. when you zoom in does yours actually have leading and trailing edge surfaces. from a distance it looks like they are there but when you zoom in there is a blank. at least for me. let me try this again as it seems you guys are having some success.

thanks again

Oooops prop, looks like my example missed one of the little arcs at the bottom for the join.. I'll review it and repost.

Hi Prop,
Yes I saww the problem you just described...Here is a file with the sweep as i think you wanted it..

I'm not exactly sure about one of the issues, and will wait for Michael to chime in.

First, the scale of the model may have been presenting issues for the tolerances in the file.. FOr instance, that little arc on top is something like .0067 in diameter..

I scaled your model up by 100 times, then tried the sweep. I still had an issue in that little top arc area with a malformed surface creation.. So I ran seperate on the 2 original profiles and seperated out that little arc on both ends (Perhaps they were joined with the small values and didnt get a good join in???) Then I used the 3 point arc command and recreated those 2 end arcs and deleted the old ones. Then I joined the whole lot and did the sweep as described before...

Then I scaled it by .01 and will attach it here.

hi, thanks now I know I'm not crazy. what you found makes sense based on my experience with rhino. I had to fight with it a long time before I got it to work. and it all boiled down to tolerance settings and mesh options mostly.

I see moi is way better in a lot of ways and can really save some time if I can figure it all out. you came up with a really smart solution I wouldn't have thought of, scaling up and then back down. I should mention all points are in meters.

Hi Anthony re: Trim -

> I have a circle I'm trying to trim with two points.

Could you post the particular circle and the 2 points in a 3DM file so I can take a look at your specific case?

Trim does work in general with a circle and 2 points - for example here I've created a circle and 2 points on it, and used the Trim command to cut away a part of it:







If it doesn't work from you possibly the points are not on the circle or something like that? It's hard for me to know what the issue might be without seeing the model file though.

- Michael

Hi Pilou,

> If you select one arsc the sweep 2 rails works
> If you select the other arc the sweep 2 rails works
>
> If you join the 2 arcs the sweep 2 Rail works
>
> If you select the 2 arcs (not joined) the Sweep 2 rails don't works

Yup, and that's all normal... Anthony, when you do a Sweep each particular "station" along the sweep should be made up of 1 curve - if you have multiple pieces then use the Join command first to join them together into one logical curve so that the sweeper will know what the profile is supposed to be at that station.

The sweeper does not know how to process multiple separate profiles that exist at a single location along the sweep - you need to configure your curves using Join so that you have one single curve at each station.

Either that, or if you want to have multiple curves at a single station then you would need to do Sweep multiple times, each time using just one of the curves at that station.

- Michael

Hi Anthony,

> I should mention all points are in meters.

With small values like this, you'll generally be better off setting units to centimeters or millimeters, rather than meters...

If you have features that approach the fitting tolerance (which in MoI is 0.001 units), it can make for some badly formed results - you want to avoid having entire features of your model that approach that size.

So instead of modeling with units = meters and using numbers like radius = 0.005 and stuff like that, I'd strongly recommend using units = mm and numbers like 5 - that will generally help to keep you away from the problem of having entire features of your model at the fitting tolerance level.

In the future I want to switch some more things to work with an "adaptive" tolerance where it uses a fraction of the size of the smallest feature that is currently being used. Some operations work like that already, but not everything. In the future when the adaptive tolerance system is more fully in place it will probably work better to use things with smaller numeric values but until that time you should avoid it.

- Michael

Hi Anthony, that little tiny arc at the top of your shape up here:



That arc has a radius of 0.00006 units - that's not just approaching the fitting tolerance, it's quite a ways under it. That will cause all kinds of various problems - basically that arc will tend to melt away since various mechanisms will think that a line is within tolerance of it as a proper shape to represent it.

Even when you work at a better scale, that little arc at the top is still really out of proportion with the rest of the shape and you'll probably run into a lot of problems with something that has such a teeny tiny rounded piece in it that is so much smaller than the rest of the surrounding model.

Really you should generally avoid creating models that have that type of way out of proportion feature in it - it throws a monkey wrench into a lot of different kinds of things.

- Michael

Thanks for all of the help everyone. I'll look into this some more. I don't know why my circle would not trim. Both points should have been on the circle. But since you got it to work, that gives me hope. As far as the trailing edge radius being very small unfortunately I can't do anything about that. That is a NACA 65A009 airfoil. I don't specify what it should look like. That is just what it looks like. I can do it in Rhino. I have to change all the default settings to do it though. I wan't to try the suggestion earlier of scaling the model way up then way down and see how that goes. I joined the entire airfoil surface together but it still made the model with errors. I hadn't mentioned it previously. But given everything everyone has said it has to be a tolerancing and dimensioning thing. I'll play around more since now I know at least in theory what I'm trying to do can work. I have the Rhino model as a part of the download to my program on my SourceForge site. I tried to upload the Rhino model here but it was too big.

The rhino model is in the examples/rhino folder within the prop_design.zip file. The reason I was interested in trying MoI is that you do have to fiddle with the Rhino settings a lot and I don't think everyone would know to do that. Also rhino can't do the fillets when you try to blend the blade to a hub. So you'd have to take it into solidworks or something. I don't think everyone has the money to do that. So ideally a low cost, easy to use, program that you can get a detailed fixed pitch aircraft propeller is what I'm looking for. Not for me, but for people that would use my program. I can't whole heartedly recommend rhino as I know it has limitations. Moreover, you can only get so far with it before you have to abandon it for an even more expensive program.

Edit; I have since closed my SourceForge project. You can find my MoI example here; http://propdesign.weebly.com/.

Hi BurrMan,

Thanks, I looked at your model and you nailed it. I will try to do it myself for learning purposes.

Anthony

spoke too soon. when i tried the method burrman used i found the surfaces at the tip near the trailing edge were malformed. so i looked at burrmans model in that region and he had the same issue. i did notice i had to redo the trailing edge arc as one arc rather than two. i had it that way because of how rhino needed it. no big deal to change though.

Changing the mesh angle option to .1 seems to fix this issue. This is a dumb one, I read the help before asking. But I'm on a laptop, I have no middle mouse button. So in the 3d view I can't pan. Is there a way to pan in 3d in this situation?

So I made it as far in MoI as I did in Rhino. Next is trying to blend the blade into the hub, which I can't do in Rhino. I tried a few things in MoI but not having luck. In rhino I can trim the blade with the hub and then do a polar array to at least get a basic idea of what the propeller looks like, but I can't have the hub blend in with the blades. In MoI when I try to trim the blade with the hub it doesn't trim it at the surface of the hub. Not sure how to blend it. Especially if there is no true intersection at the hub.

Right now the MoI model is scaled up 1,000,000 times its true size with default settings, so that the trailing edge radius comes out right. A polar array about zero using 8 blades would give the finally propeller.

hi there

..regarding PAN in 3D-window:



best wishes,
marco