topic Re: My loft is twisted incorrectly around each construct plane in Fusion Design, Validate & Document Forum

My loft is twisted incorrectly around each construct plane

simon.dyer — Sat, 15 Jul 2017 12:33:15 GMT

In these pictures you will see my problem easily - the loft through each rib is not aligning up with the points in the sketches. You can see the sketches are correct when I overlay them - both have 30 points defining the curve starting from the rear, however the loft seems to select diferent points or even creates them magically.
I can move these points manually, but that is long and tedious and inaccurate. The sketch points are correct and need to be used by the lofter. See the leading edge this is not right - all twisted around.

Solutions anyone please?

Re: My loft is twisted incorrectly around each construct plane

davebYYPCU — Sat, 15 Jul 2017 13:11:53 GMT

Use Fusion Splines to trace your airfoils.

I use four point Spline, for top and bottom.

If using a csv file, use the script to plot the Spline.

Might help...

Re: My loft is twisted incorrectly around each construct plane

jeff_strater — Sat, 15 Jul 2017 13:57:49 GMT

Hi @simon.dyer,

@davebYYPCU is correct. What you are seeing here is what we call "Point Mapping" in Loft. It looks like your input sketches have many small curves in them. The modeling kernel in Fusion will create an edge in the model where each curve meets with another. Each loft section, then, can have many points in it. Loft tries, then, to map each point on each section to a point on the next section. Most of the time, it does a pretty good job. But, if there are many section points, the mapping can be difficult. You can adjust the mapping by dragging the points around. If you need, I can record a screencast of how to do this, but basically, it's just click and drag on the white points in the preview. But, in this case, it will be tedious for you to do this. There are just too many points. And, if you don't have the same number of points on each section, the mapping gets difficult anyway.

So, what I would recommend is: Keep your existing sketches. In each sketch, select the curves you have, make them construction, and re-trace a single, or at most a couple, of Fusion splines over top of those curves, matching them as closely as possible, and most important, keeping the number of curves in each section the same. Then, your loft should behave much better.

If you want to share the model, Dave or I, or someone else will be happy to help.

Jeff

Re: My loft is twisted incorrectly around each construct plane

simon.dyer — Sun, 16 Jul 2017 02:42:00 GMT

Whilst both solutions might be okay in the long run, this is an iterative design process - I need to import my wing ribs many times, and loft them. (Maybe actually update the sketches).

The script CSV option might be better if it can connect up to my sketch points (30 in each sketch) - is there a link explaining that process?

Re: My loft is twisted incorrectly around each construct plane

simon.dyer — Sun, 16 Jul 2017 02:58:37 GMT

@davebYYPCU

Can you point me to something explaining how to do this scripting?

Re: My loft is twisted incorrectly around each construct plane

davebYYPCU — Sun, 16 Jul 2017 22:31:09 GMT

Couple of things, csv file, is Comma Separated Values, a saving format for numerical data points, in spread sheets, I use Excell.

If your data is two columns you need to add a third column for the plane you wish to import to, eg import to XY plane, the Z values would be zero.

Csv is not the default format in Excell so it's Save as, and select the type, CSV.

This screencast helped me at the time, https://screencast.autodesk.com/Embed/Timeline/c1d0d5f5-17a4-485b-86dc-5330e0cba236.

These days I do as Jeff mentioned, trace an imported airfoil using snap points and the tangent handles, for a top then bottom Spline.

Constrain the leading edge handles to vertical, and trailing edge handle to conform to the underlying imported sketch, and have not used the CSV lately.

Fusion Splines are smooth, you don't need the 30 data points you started with to have the same accuracy, but you still need to have the same number of fit points in each airfoil.

To save a library of common airfoils, save the sketch out as dxf, and import when needed.

Might help....

Re: My loft is twisted incorrectly around each construct plane

simon.dyer — Mon, 17 Jul 2017 00:20:35 GMT

Thanks @davebYYPCU,

Yes I assume I can import CSV as smooth splines for each sketch, once I figure out what is causing this error message:

Including the Z data in one go is terrific.
BUT

Problem is my design is complex with changing airfoil shape along the length of the wing, and scale and twist all designed which I wanted to be accurately represented when I loft.

IE I am still left with the problem that the loft doesnt align the points on the sketches, and messes with my leading edge.

Whilst the explanation from Autodesk @jeff_straterthat it finds its own points along the sketches is nice for some shapes I am sure, that algorithm should be guided by the points on the curve, especially when all the curves have 30 points.

Maybe I should submit an idea on that.

Re: My loft is twisted incorrectly around each construct plane

simon.dyer — Mon, 17 Jul 2017 00:28:26 GMT

Okay - solved the import error - I was selecting the wrong export format in Excel - cvs UTF-8, need to use plain csv

Re: My loft is twisted incorrectly around each construct plane

simon.dyer — Mon, 17 Jul 2017 01:02:59 GMT

Okay big improvement, but dont understand why importing each sketch as a SVG is so much different to importing as a csv script - clearly it is better, but unsure why loft got twisted in the earlier case.

I didnt do any tracing of the curve - not sure why that step is necessary @davebYYPCU

Now I just need to to figure out why I cant change the control handles on certain points, and how to encourage the loft to follow each sketch, not draw straight through as it has on the TE.
Then I'll have a nice tool chain to develop my plane.

Re: My loft is twisted incorrectly around each construct plane

simon.dyer — Mon, 17 Jul 2017 03:07:25 GMT

Okay nearly there folks. Thanbks for all the help.

Resolved:

1. The weird trailling edge line in the last post was my error - I had a previous lofted body display that went from root to tip directly.
2. The lump in the leading edge - dont know why, but I reimported the root sketch and all was well.

Still a problem

3. I cannot get the parts that should not spline to reduce the effect and be a line - pulling on the handles makes things go nuts.

Please see screencast

http://autode.sk/2v8kISX

Re: My loft is twisted incorrectly around each construct plane

davebYYPCU — Mon, 17 Jul 2017 06:04:45 GMT

Why so many profiles? Wait till you start adding rails, then you will see how loft can give trouble.

The screencast shows me a few things, you have more than the current sketch visible, I would turn all the others off, (Fusion is trying to help but gets it wrong sometimes)

looks like the low end of the spline handle has been constrained to that other sketch line, you and I know you don't want that but while it's visible Fusion will try to annoy you with it.

(at least while you are editing it.

When you do get to move the handle it also shows me that you have one spline, likely from top of trailing edge to bottom of trailing edge, here 2 works better.

A top one and a bottom one, especially to handle undercamber.

You have 13 visible points on the top of the tip rib, probably the same for the lower side, too many points makes things worse not better.

You have told us about an error in the screenshot, is there a better one, can you attach a test wing for demo purposes?

It looks like an undercamber at the root rib and symmetrical to a degree at the tip, Fusion will transition those two profiles, you are working too hard to make Fusion think.

Could be wrong, would like to help...

Re: My loft is twisted incorrectly around each construct plane

davebYYPCU — Mon, 17 Jul 2017 08:14:07 GMT

I have attached a test file, to demonstrate, what I am saying,

The first sketch is your supplied file from the import thread,

the second sketch highlights how the splines can match the original with a few well selected points, projected from the original.

Use the light bulbs to check the accuracy,

The original file has no 0,0 data point, unusual, so its mine, and the Trailing edge is open, 5.8 degrees of incidence is a lot.

What are you modelling, and does it have to be 100% accurate, to "that" root rib?

might help...

Re: My loft is twisted incorrectly around each construct plane

simon.dyer — Mon, 17 Jul 2017 09:30:08 GMT

@davebYYPCU Thanks for your interest - Im modelling a Horten style 3m wing. So its a big project, therefore Id prefer that the data used is the same as gets imported to be "100% accurate" with the designers intention.

Since most of the splines look okay, it seems I just want to convert the segments near the trailing edge to be lines, so they dont try to skew everything. If I was doing this in Adobe illustrator I would just reduce the handles to zero length to stop the splines curving the shape where I did not want them to. I dont know why I cant do that here.
Im not sure how you are referencing the 'original file' - I haven't uploaded it. The Root rib does start at the origin. And the TE are all closed to form a closed sketch, otherwise lofting is even harder for me.

I can hide the other sketches and demonstrate the problem the handles are giving me in another screencast....

Just for clarity, I have solved most issues with workaround (import csv not SVG) this image shows the final problem Im trying to resolve.

Re: My loft is twisted incorrectly around each construct plane

davebYYPCU — Mon, 17 Jul 2017 10:56:39 GMT

You posted an example rib in another thread, Import XYZ data to Fusion 360. Root.csv.

I have opened it, and there was no data point for X0 - Y0. The Trailing edge was not closed, as the first and last set of data points are not identical.

I know the Horten wing, a modeller here built one as a slope soarer, and I saw it fly about 2 years ago. I am not so sure it was as big as 3m, but it could have been.

I also did a 2m twin electric DF IX/229 version quite a few years ago.

Adding lines to the trailing edge will work, but break the Leading edge at Y0, or the Mapping points will not be controlled the way you need it.

I would use first and last rib 6 rails, LE TE, top and bottom Main Spar, and top and bottom Aileron Spar. when done check the result with sections that match your data.

Re: My loft is twisted incorrectly around each construct plane

simon.dyer — Mon, 17 Jul 2017 11:10:37 GMT

Ive tried to demonstrate my problem here:

http://autode.sk/2v9c7Qc

I cant seem to find anything about this. If the control handle is constrained, then I want to delete the constraint, right? Where is the thing to delete. And why does it change from blue to green?

Re: My loft is twisted incorrectly around each construct plane

davebYYPCU — Mon, 17 Jul 2017 11:41:34 GMT

When you edit sketch, the handle point is not attached to the top Spline section, but I couldn't see what you did to make it snap onto the Spline not long after that, and the top section is acting like the handle end point is a fit point as well, that could be a bug.

Then about the 20 sec mark, you select and place a fix constraint to the end point, which has turned green, and has locked the handle in place from that point on, I didn't see you unfix it.

You can only move the Spline handles when selected and turned lime green. If by chance the csv import makes the sketch a 3d sketch without telling anyone, then you can only move the handle end points with the Move command. - I would try that to establish if it is now a 3d sketch, even if unintentional.

Might help...

Re: My loft is twisted incorrectly around each construct plane

simon.dyer — Mon, 17 Jul 2017 12:35:58 GMT

Thats definately a help - and apologies - such a newbie - Id found that before - that I had to select move to get the handles to move. So now I can tidy up the trailing edges. But they still go a bit wild, which I'll demonstrate once it finishes crashing and restarting

Re: My loft is twisted incorrectly around each construct plane

simon.dyer — Mon, 17 Jul 2017 13:26:35 GMT

@davebYYPCU, many thanks for your help. Ive done a screencast of this final problem with the handles.

I wish I could just convert some of the sections of the spline into polylines. Then I could have sharp corners.

http://autode.sk/2u19Ms7

Re: My loft is twisted incorrectly around each construct plane

jeff_strater — Mon, 17 Jul 2017 15:04:57 GMT

Thanks, @simon.dyer, your comment helped me to figure out what is probably going on with your spline handles. Because you are not able to just drag them, you probably have (maybe inadvertently) turned your spline into a 3D spline. Dragging does not work on any 3D sketch geometry, but Move does. Because you are able to use Move to adjust the handle, this is probably the problem.

No worry, though. Select the spline, right click, and choose "Move to Sketch Plane" (or something similar, I'm at the airport, and don't have Fusion in front of me). That should move the entire spline back to the sketch plane, and you should be able to drag the handles again.

At one point in your first video on the handles, while you are trying to debug them, you chose "fix/unfix" on one of the handle points. I suspect that this had the unintended consequence of fixing a point that was not fixed before. You will probably need to un-fix that.

Trust me, you do not want to use polyline for this project. That will get you back into the point mapping problem that you had at the beginning. Stick with the splines - you are getting close!

Jeff

Re: My loft is twisted incorrectly around each construct plane

davebYYPCU — Mon, 17 Jul 2017 21:30:14 GMT

Oh that is so painful to watch, I wanted to turn it off by 3/4 of it.

All your problem is

is that you have 1 Spline, closed to be a loop, never gunna happen,

any move adjustment effects the curve wider out than just the point you selected

Splines are curves, you can't have a sharp point, unless you join two together, (Top and Bottom splines to make an airfoil)

Please open and review my example file from post 12 above.

Download it, save to hard drive, then in Fusion,

File > New Design from File.

Use light bulbs to examine how close the overlay is.

Honest - I moved 4 handles once to get there, added 2 constraints. Amongst some other stuff.

As my day unfolds I will try to get a screencast done, would be better if you export your file so I can teach with your data,

File > Export, attach to a post.

Stick with it.