Editor glitch. Looking for a workaround.

[Aeroboi]

I've been working on several Eve ascent vehicle designs for a Eve challenge. I did a lot of testing how I can do it with very few funds and already made something worthy but I found several tricks to make it even better and I'm going to make my newest version if I can get past a very annoying bug.

I have made a decoupler/staging system with which I can stage pivot a engine at a static angle that is normally not able to pivot at that angle through it's default gimballing.

Issue im having.

The problem is that the fairing that shields the system from drag has a big problem. When I build the fairing the vessel becomes bugged in that I cannot connect any fuel lines (fuel ducts) anymore on my vessel. The same goes for struts I found out. The exact anomaly is that I can start to connect the strut to the parent part (1st part I click on) but then disappears when connecting to the client part with the clicky clicky sound as if it were connected regardless without actually connecting.

It isn't game breaking because I can save the top stage as a sub assembly and build the fairing during subsequent tests and when I finally build the vessel.

Still this is very annoying and I hope this bug is being reported before and that there is a workaround, hopefully...
If there isn't I will file it personally. I hope that a certain feature of this system is what triggers the bug and that people can tell what that might be. Below I have a description on how it works.
I'm gonna do some testing first and then post a craft file, hopefully people with good editor skills may be able to detect what part or combination of parts are causing this bug.

Furthermore: Rebuilding the pivoting system doesn't solve it. I already thought of this. Whenever I rebuild it and re-save the subassembly, re-reconnect it to my craft and build the fairing anew the fuel duct bug comes back around. Below is a picture of the craft with the system I made and there under a album of the staging sequence while being able to climb at 90 degrees without SAS so you guys have a idea what I made.

Album: https://imgur.com/a/S4yoEPM

 

How it works: It's remarkably simple to be honest but took me quite a lot of time to figure out while being able to shield it and keep it low weight.

The Skiff engine is attached to the radial decouplers. The radial decoupler works like a spring. Any part that is attached to it while being moved away from the parts center will spring up and down. The farther the distance, or the more decoupler you stack the more loose the spring becomes and the more distance a attached part can pivot.
To the decoupler I attached a jr docking port. I then rotated it 90 degrees and moved it to the left base of the engine plate with the port facing up. I then autostrutted it to grandparent part (the decoupler) so it moves stiff with it when it and the engine pivots up and down.

The default state of the system is that the engines are locked in place in a default snap on position. To do this I put a mini probe core on top of the docking port jr. I strutted the probe core to the tank and to the engine. Because the docking port is attached to the decoupler and the probe core to the docking port which is now strutted the mechanism can't move.
When I set the docking port to the staging sequence whenever I drop a lateral stage the probe core and the struts disconnect and the mechanism becomes free. Because the engine is under thrust the engine bell will pivot at a desired angle. When I stage the engine pivoting system opposite of the dropped lateral tank the thrust realigns and my rocket keeps going straight.

To create the desired angle is by adding or retracting decouplers and by moving the engine inwards or outwards relative to the position of the decoupler. Finally I tweak it and re-move the system and engine radially to recenter the engine.

The system is then faired within a fairing. Using the local coordinate space Move tool function I can very precisely recenter all the parts so a fairing below the thrust plate can shield the engines from drag also. They aren't because they aren't actually attached to the thrust plate. The thrust plate is there because it's light and to function as a attachment for the fairing to close at. Which is what creates the bug when i try to build the fairing, unfortunately.

 

Edited October 6, 2018 by Aeroboi

[Rocket In My Pocket]

A possible workaround would be to use the fuel priority system instead of fuel lines, and auto struts instead of regular struts?

They have their own limitations though and may not work for every purpose.

Edited October 6, 2018 by Rocket In My Pocket

[Aeroboi]

9 hours ago, Rocket In My Pocket said:

A possible workaround would be to use the fuel priority system instead of fuel lines

I thought about this but I never understood the fuel priority system although I got it to work occasionally. The numbers are completely arbitrary to me. How do they make sense?
Is there a text or video walkthrough that properly explains the fuel priority system?

What struck me is that one tank has a fuel priority of lets say 40 (0) and another tank -10 (0)
Why is one -10 and the other 40 and what makes priority change when making it + or - from (0)?
Also, I always thought you required a fuel line or a fuel feed system besides the fuel priority settings to make asparagus staging work in the first place? Is this wrong?

Another thing to know is that this rocket is going to be complicated in its staging sequence to begin with, more so as I will use my new found method to stage laterally.
So I want to use Mechjeb for autostaging and next to that I want to pilot the roll of the vessel to use the lateral thrust during ascent (like the spaceshuttle does) for extra efficiency.

The problem is, Mechjeb doesn't properly calculate Dv when using the fuel priority flow system in complex asparagus staging. And that is when I can get the fuel priority system to work which I'm not always able to.

10 hours ago, Rocket In My Pocket said:

and auto struts instead of regular struts?

I already use autostruts everywhere besides that mechanism. The mechanism must be fixed against the closest parts but that isn't the grandparent part for it to be fixed from any motion and heaviest and root part are to far away from the position of the mechanism to achieve that. So I require the strut part for this. A part I must say I rarely use but for this mechanism I found it's required.

10 hours ago, Rocket In My Pocket said:

They have their own limitations though and may not work for every purpose.

Unfortunately that is the case here, but I stress to say... "AFAIK"

[Foxster]

Once you get your head around the fuel priority thing it's actually pretty simple and, no, you don't need ducts for asparagus staging. 

How it works is that if there is a number of tanks that could supply fuel to the current stage's engine(s) then the tanks with the highest priority number get used first. Low numbers can go to zero and into negative. 

Take this simple craft...

A common thing to want to do is use the lowest tank first and the upper second to keep the CoM high to improve stability and prevent flipping. So, checking both tanks, we see that the Flow Priority is -10 for for both tanks and by default they will be emptied together. But if we click the "-" button on the top tank and change it's priority to -11 then it has a lower priority and will only be drained once the lower tanks is empty. 

Now for asparagus...

KSP does a pretty good job of guessing what you want to do and sets the priority for you. So, in the craft above, it left the original two tanks at -10 and -11 and new drop tanks it set to 0 (higher priority). You need to Enable Crossfeed on the decoupler to allow fuel to flow without a duct. 0 is higher than -10 or -11 so those outer tanks will empty first, you can then drop them and the lower of the two centre tanks will start to drain. 

Mechjeb can cope with this fine once you Enable Crossfeed. It will calculate dV and manage staging OK. If you have something complicated going on then it (or more often, you) might struggle to figure out dV and staging, in which case you can add ducts and it will calculate dV OK and you can then remove the ducts later to save the weight and drag of them. 

 

Edited October 7, 2018 by Foxster

[Aeroboi]

@Foxster Thanks

I'm going to put in some effort to get the staging working properly with the priority system as you instructed it.

One thing that really baffles me is that some tanks automatically start with a certain number that to me is nonsensical. I have a center tank for instance which defaults to 40 but some of the outer tanks are -10. Is there some logic why tanks start with these random numbers? I think having them all set at 0 by default is less confusing to a player like myself or anyone I'd assume.

[MaianTrey]

21 hours ago, Aeroboi said:

Issue im having.

The problem is that the fairing that shields the system from drag has a big problem. When I build the fairing the vessel becomes bugged in that I cannot connect any fuel lines (fuel ducts) anymore on my vessel. The same goes for struts I found out. The exact anomaly is that I can start to connect the strut to the parent part (1st part I click on) but then disappears when connecting to the client part with the clicky clicky sound as if it were connected regardless without actually connecting.

It isn't game breaking because I can save the top stage as a sub assembly and build the fairing during subsequent tests and when I finally build the vessel.

Still this is very annoying and I hope this bug is being reported before and that there is a workaround, hopefully...
If there isn't I will file it personally. I hope that a certain feature of this system is what triggers the bug and that people can tell what that might be. Below I have a description on how it works.
I'm gonna do some testing first and then post a craft file, hopefully people with good editor skills may be able to detect what part or combination of parts are causing this bug.

Furthermore: Rebuilding the pivoting system doesn't solve it. I already thought of this. Whenever I rebuild it and re-save the subassembly, re-reconnect it to my craft and build the fairing anew the fuel duct bug comes back around. Below is a picture of the craft with the system I made and there under a album of the staging sequence while being able to climb at 90 degrees without SAS so you guys have a idea what I made.

I have this issue when using about 3 or more fairings on the same vessel in the VAB (my shuttle craft, for instance). My super easy, no fuss work-around is to hold ALT when clicking the second part of the strut/fuel line. What happens (for reasons I don't know) is that the second part is automatically double-clicked, so it places the fuel duct/strut and immediately picks it up. Holding ALT instead places, and then COPIES it, so the original stays. Then you just hit Delete or click in the catalog area to get rid of the extra part.

Edited October 7, 2018 by MaianTrey

[Rocket In My Pocket]

13 minutes ago, Aeroboi said:

One thing that really baffles me is that some tanks automatically start with a certain number that to me is nonsensical. I have a center tank for instance which defaults to 40 but some of the outer tanks are -10. Is there some logic why tanks start with these random numbers? I think having them all set at 0 by default is less confusing to a player like myself or anyone I'd assume.

I don't know the nitty gritty details but it attempts to set up a fuel priority that makes sense given the staging and such.

So if you make a plane, and put a drop tank on it with a radial decoupler, it'll auto set that tank to a higher priority so it drains first as it intuitively should.

I have no idea why it chooses such wildly different numbers when being only 1 above or below is sufficient.

[Foxster]

2 hours ago, Aeroboi said:

One thing that really baffles me is that some tanks automatically start with a certain number that to me is nonsensical. I have a center tank for instance which defaults to 40 but some of the outer tanks are -10. Is there some logic why tanks start with these random numbers? I think having them all set at 0 by default is less confusing to a player like myself or anyone I'd assume.

I think KSP has a good go based on order of placement and such but it makes less sense once you start messing about with the craft, especially with asparagus and such. You'd be lucky with anything other than fairly simple craft if the priority worked by default and will almost always require manual adjustment.

The big gaps between the numbers is presumably to allow for extra tanks to be added in the middle without needing to re-order all the existing tanks e.g. add a tank with priority of 5 between existing tanks with 0 and 10. Being able to go negative is a similar cunning thing; it means you can always add a tank with lower priority, which you couldn't do if the lower limit was zero and you already had a tank at that priority. 

[Aeroboi]

20 hours ago, MaianTrey said:

I have this issue when using about 3 or more fairings on the same vessel in the VAB (my shuttle craft, for instance). My super easy, no fuss work-around is to hold ALT when clicking the second part of the strut/fuel line. What happens (for reasons I don't know) is that the second part is automatically double-clicked, so it places the fuel duct/strut and immediately picks it up. Holding ALT instead places, and then COPIES it, so the original stays. Then you just hit Delete or click in the catalog area to get rid of the extra part.

This is exactly as it appears to be. As I experience it happens when building multiple fairings in symmetry at the same time, which is the case. Holding Alt does indeed circumvent the bug. I recall I have build fairings in multiple way symmetry before and haven't had the bug occur to me then so maybe it's still something else, I'm not sure. I'm trimming my mechanism for the best pivot angle to minimize cosine losses still so I will rebuild the fairing quite a few more times and hope to find out how the bug is exactly triggered. Workaround or not I think this shouldn't happen in the first place.

@Rocket In My Pocket @Foxster I got it worked out and I probably gonna use this system from now on, always. No ducts = Less parts and less drag and weight and should be a mandatory designer rule for a efficient Eve ascent rocket.

Thanks for all your input

 

[Laie]

On 10/7/2018 at 4:25 PM, Aeroboi said:

One thing that really baffles me is that some tanks automatically start with a certain number that to me is nonsensical.

Usually, it starts out at -10 for the last stage, then adds another ten for every stage below that. It automatically discounts any stage that doesn't have a decoupler, and it re-prioritizes the tanks whenever you manually move a decoupler to another stage.

Usually this works very well, but sometimes the system gets a hiccup and assigns silly values.

Fuel priorities are simple: bigger numbers are drained first.

Important: fuel lines don't override this. They provide a path where fuel can flow if otherwise it couldn't, but if the line leads from a small number to a big number, the big number will still be drained first.

Other than that, this auto-balancing asymmetric staging deserves a design prize in and of itself. Great work!

[bewing]

On 10/6/2018 at 9:33 AM, Aeroboi said:

Still this is very annoying and I hope this bug is being reported before

I don't think it has, but I've spent a week trying to figure out how to do it, and I've failed. I need clearer instructions, or a very very simple test craft that shows the bug.

 

[Aeroboi]

4 hours ago, bewing said:

I don't think it has, but I've spent a week trying to figure out how to do it, and I've failed. I need clearer instructions, or a very very simple test craft that shows the bug.

 

@bewing I don't know what triggers the bug myself yet, so I don't know what to instruct.

The craft in the OP wasn't build with the "proper" aerodynamic housing and still causes drag. I feel no hesitation to share the craft file with you or anyone else for that matter as that version is unfinished, I do have one that is.

Download: https://www.dropbox.com/s/germ8dgdsdshy61/The Oreman XLII.craft?dl=0

Build the fairing above the engines on the boosters. Then add a fuel duct or strut and then click anywhere on the vessel to connect it and watch to see the bug happen.
Do the same thing again but then by holding Left Alt. Now it works!

 

[mystifeid]

On 10/7/2018 at 6:27 PM, Foxster said:

Mechjeb can cope with this fine once you Enable Crossfeed. It will calculate dV and manage staging OK.

Strangely enough, Mechjeb seems to manage staging tanks ok, but put engines under those tanks and it refuses to stage them unless fuel ducts are used. Though maybe I'm missing something.

[Laie]

On 10/12/2018 at 12:38 PM, mystifeid said:

Strangely enough, Mechjeb seems to manage staging tanks ok, but put engines under those tanks and it refuses to stage them unless fuel ducts are used. Though maybe I'm missing something.

Nah, you're right. MJ assumes that any engine will be kept for as long as it is working. And KER does, too. The two used to have different philosophies sometimes, but (quick check) I can't produce an example right now.