HELP NEEDED: Star Destroyer frame build

[TheGeneralMoe]

Hey everyone

So i am building a Imperial Star Destroyer, which is being documented in another topic, but i have encountered issues with the frame. I am having difficulties with its build, from aligning the panels at an angle that fits well to building a stable frame that doesn't but strain on joints due to forced connections.

I have seen many great SD builds on here, and i was looking for advice and techniques to help me get this right.

This is my first attempted layout. It looks fairly fine, though as i continued to make structural reinforcements and increase its length, problems arose. Also, this angle seem a bit 'shallow', and probably should be raised slightly more.

Here is the frame currently. I need the middle beam, in order to help with the stand that will come out of the destroyer's hanger. There is the issue of the centre beam pushing against the cross supports, creating tension that may damage the pieces.

Any help would be great, as this is an important part of the build and i can't progress until i find a stable design.

Thanks!

[NathanR]

A year or so back I was looking to build 10030 using modern parts/techniques, and I experimented with enlarging the technic frame that was used in 75055.  I got a UCS-sized frame with four support beams that seem to fit within Lego tolerances, but the angle meant a nasty seam down the middle of the ship for the triangular hull plates.  I never got any further with the design, but I share the LDD file in case it helps you:  https://www.bricksafe.com/files/NathanR/techniques/randomtechniques/03_ISD_Framework.lxf

Good luck with your star destroyer!

[CPGamers]

I think it is looking good so far

[Raskolnikov]

That's the trick, isn't it? I totally thought this part would be easy, then I spent like a month working through similar problems. The easiest path forward is probably to copy the pattern that the 75055 frame follows (i.e., just count how much longer each beam is, how much hinge placement changed, etc., then replicate). You can then maybe play around with how you attach the panels to limit the seam down the center.

Really, there aren't all that many non-illegal options to create an A-shaped frame with a decent number of cross beams. If you want to mess around with other possible angles for the frame, it'd probably help to brush up on your algebra and trigonometry to find out why some builds work and others don't. Let's take a look at your frame, by way of example:

You've made a right triangle with one side 18 studs long (green) and one side 6 studs long (red). In order for the build to not be illegal, we need the hypotenuse (blue) to be pretty close to a whole number. In this case, you've done a good job with that. The Pythagorean theorem tells us the hypotenuse is 18.97 units long, which is pretty close to 19 studs. That's why connecting these beams together probably felt right, while other connections did not.

One problem though is the angle. Your exterior panels are using 3x6 wedge plates, which have an angle of 18.4 degrees. Turns out, each half of your frame has the same angle. So if you continued this pattern and built the frame in sturdy manner, then attached the panels to the sides of that frame, the panels would lie flat. At the moment, you can create a gentle slope (as shown in the earlier picture) but it's due to a few millimeters of bending along the sides of the frame, or the panels being placed on the frame a few millimeters off, etc. You can calculate the angle by googling arctan calculator and plugging in 6/18 (opposite side over adjacent side). And the result is the same for a 3x6 wedge plate (which includes a right triangle with sides of 2 and 6).

In order to get a gentle slope towards the center of your ship, you'll want each side of your frame to create an angle closer to 18 degrees (yeah, the .4 is important...my Star Destroyers are relatively deep, and I think my angle is around 17.8). I forget exactly what the 75055's angle is, but you can figure it out if you draw triangles like I drew above. As you'll see, putting the hinge plates in different places can allow you to create some new angles. The 75055's frame has the hinge plates in the middle of the cross breams, creating two right triangles on each side (so you have to calculate the angle of both, then add them together to get something that's probably pretty close to 18 degrees).

Anyway, GL!

Edited May 13, 2018 by Raskolnikov

[TheGeneralMoe]

On 5/11/2018 at 6:38 PM, NathanR said:

Good luck with your star destroyer!

Thanks for the help, though i assume if you ran into similar problems they may spring up for me too.

 

6 hours ago, Raskolnikov said:

That's the trick, isn't it? I totally thought this part would be easy, then I spent like a month working through similar problems. The easiest path forward is probably to copy the pattern that the 75055 frame follows (i.e., just count how much longer each beam is, how much hinge placement changed, etc., then replicate). You can then maybe play around with how you attach the panels to limit the seam down the center.

Anyway, GL!

Thanks for the advice, its quite mathematical, which i have started implementing. I have the FO star destroyer, which has a similar frame to 75055, but more importantly has a very clear 'A' connection with middle beams present in the build. I have started from there and did some calculations of the pattern of the build:

The build starts at the nose with a 4 stud wide centre with 2 stud angle. the build is parted by 20 studs until the next frame, which has the middle increased by 6 studs and the angles doubled to 4 studs. The back of the ship has a centre of 16 with angles of 8. following this pattern, the next is a 24 stud long centre with 16 stud long angle.

Now I'm not too sure how stable this 24-16 combo will be, if adjustments will need to be made, but if the first 3 are stable, it should be good from there.

https://www.flickr.com/photos/154087455@N04/27203757597/in/dateposted-public/

Concerning how deep the panels will be, that will probably come down to more trial and error, and some strategic placement. What connectors i use also depends.

Thanks for all the help!

[Jerac]

Initial photos in the first post show an old-school frame which was so meh I couldn't really recommend anything except "redo it from scratch", but this latest version I see is already much better! It is very strong, braced with liftarms - good way to go!

As for the connectors, put them *inside* the frame, not outside. Hull plating is sloped, meaning gravity will try to pull it outwards, which will also try to pull out your connectors from the frame. You can try to brace them or you can use geometry to your advantage - if you put these connectors to the inside, they will be pushed into the frame all by themselves!
Now for the bottom plating the situation will be reversed: connectors installed on the outside of the frame will be pulled towards it (which is good), so all in all I guess you need to have them on both sides.

If your ship is going to be sufficiently big, you will discover the nose will droop. This is because a "legally-built" frame has some slight gaps between pieces and under enough weight, they will close. You will have two options to solve this:
- introduce stress in the build deliberately. Stress already closes these gaps I mentioned and gives you more control of frame's behavior, but it will indeed bend the pieces. I had no option with the 2-meter long SD but this was really extreme case.
- make an angled beam running along the center beam, to make the frame triangular also when looking from the side. 

Black part is what you're doing right now.
Blue part will solve the problem with drooping nose if you have it.
Green beams could be useful for attachment of the hull plating.

[TheGeneralMoe]

On 5/13/2018 at 4:55 PM, Jerac said:

Initial photos in the first post show an old-school frame which was so meh I couldn't really recommend anything except "redo it from scratch", but this latest version I see is already much better! It is very strong, braced with liftarms - good way to go!
If your ship is going to be sufficiently big, you will discover the nose will droop. This is because a "legally-built" frame has some slight gaps between pieces and under enough weight, they will close.

Thanks for the advice, i will deftly consider some of those framing methods. As for nose drooping, I'm not too concerned about it happening, ad the nose will be fairly light, with most of the support focused around the centre and rear of the ship. I suppose in your model that the dense nose definitely needed to be adressed.

Current frame progress. It is going well, i have the build very sturdy and stop, with the frames in the locations i want. No 'illegal' builds present, which is good, and i am happy with the angle the panels rest on at the moment. Building is back on track!

Thanks again everyone for taking the time to help!