Delta V readout bug, engines not detected

[maphi100]

Hey guys I'm new in the forum and seeking for help. 

The engines are working fine, but maneuver nodes and dV readout are broken. 

Can anybody explain to me why this is happening and if this can be fixed? I can't really use this craft, except by manually calculating start mass and end mass before every burn.

Restarting the game didn't fix it. Neither did redocking the craft. I imagine this is a pretty casual bug even though I couldn't find any posts about it. 

I have a few visual mods but stock parts and physics. I'd really love to know if there is a fix to this problem. 

Thanks for the help

https://imgur.com/hmQKEGO

Edited January 27, 2020 by maphi100
Different link to picture

[HvP]

Hello @maphi100 and welcome to the KSP forum!

Unfortunately, it's hard to diagnose a problem with the craft without more information about it. And since we can't upload pictures directly to the site, you'll have to upload to a photo hosting site and then post the URL link for the photo here for us to see. Imgur is a popular image hosting site to use on this forum because you don't need an account there to upload and post.

There are a couple of bugs in the game that are known to mess up the delta-v readout. Changing the fuel priority for tanks can do it, so can the engine plates from the Making History DLC.

One thing that would be worth checking is if you need to rearrange the stage icons in the staging stack on the side of the screen. I've noticed that some stages leave behind an empty or unused icon in the staging list, especially if they are activated out of order. This can confuse the delta-v readout. Try dragging unused stages up to the top of the staging list and see if it changes things. You might even need to separate certain engines into their own stage group, which you can do by clicking the plus sign (+) beside the stage icons and dragging the engine icon into the new spot.

There was a bug where delta-v was not shown once entering into the sphere of influence of the Mun. I haven't seen it recently so it may have been fixed in the last update, but it could still be around for some players.

As far as I know, visual mods should not cause these bugs.

Edited January 26, 2020 by HvP

[maphi100]

First of all thanks for the fast reply. 

13 hours ago, HvP said:

Unfortunately, it's hard to diagnose a problem with the craft without more information about it. And since we can't upload pictures directly to the site, you'll have to upload to a photo hosting site and then post the URL link for the photo here for us to see. Imgur is a popular image hosting site to use on this forum because you don't need an account there to upload and post.

I actually included a screenshot of my craft and staging and I can see it but apparently you can't. I'll postthe link here again maybe it works this time:

https://imgur.com/hmQKEGO

Changing the fuel tank priority would in this case do nothing because there is only one LF tank that I'm trying to use. Before docking the part of the craft with the engines was seperate and worked without and problems. This state can actually be reproduced by undocking again. 

I might try removing the engine plate but it worked  fine before docking so the docking itself should be the problem. The craft has also never entered the muns soi. 

Thanks again for your help, hopefully the picture works now.

Edited January 27, 2020 by maphi100
Different link to picture

[HvP]

Ok @maphi100 I recreated the basics of your designs and I seem to have figured out a workaround. This doesn't fix the underlying bug, but it should give you a usable readout if you follow these steps.

1) Go the staging list on the left side and create a new blank stage with the plus sign below the engine stage, as pictured below. You'll notice that the delta-v info appears, but not with your engine icons.

2) Just drag the new stage up to the top of the column, but don't remove it. Leave it empty at the top.

Now the staging list looks mostly correct with delta-v info complete for your engines and maneuver nodes are correctly calculated too. If you try and delete the blank stage by clicking the minus sign the error appears again with no delta-v info showing. Weirdly, the bug kept happening for me even after I undocked from the other vessel. Repeating the steps to create a new blank segment at the top always resets it back to normal.

I'm not sure why it's doing this, but at least it seems there is a way to get it to read correctly and the extra blank stage isn't much of a concern.

I hope this works for you, too. Good luck!

 

[maphi100]

@HvP Unfortunately this does nothing for me. All I can see is a little 0 m/s flashing up for a second when I create a new stage. 

Other than that nothing happens. 

 

I then docked a different engine part but that didn't fix anything either. That broke the dV calculator thing (does it have a name) even more and I couldn't add or remove stages anymore but I could fix the issue by reloading the save. Weird. 

However, I rebuilt the entire craft in the vab and will take my dV and twr readouts from there now by adjusting the fuel level. 

Let me hear if you find a different way to fix the problem and I will try it out, but this should work for now. 

Thanks again and have a nice day.

[HvP]

Well this is really weird.

So I went back to my test craft to see if there was any common scenario that caused my fix to not work. I tried flipping the segments around, using a different root part, turning on and off fuel crossfeed, changing the fuel flow priority. Nothing broke the fix with the extra stage - UNTIL...

I added an extra docked segment onto the end of the free docking port. You have three segments docked together and I only tried mine with two. Guess what?

When I added a third segment the fix didn't work anymore. BUT...

When I added a third blank stage at the top of the list the fix started working again! How odd. It looks like the number of docking ports in the stack is the variable that causes this bug to show up.

To confirm I reverted and tried a different configuration with a fourth segment. Sure enough it needed a fifth blank stage before the fix would work. BUT if I left out a docking port and connected the butt of one fuel tank directly to the bottom of the docking port above it, the whole configuration only needed four blank stages in the staging list for the fix to work - or five total if you include the engine stage.

So this is definitely related to how many extra docking ports there are above the engines. With this nuclear configuration it looks like you need the total number of stages in your staging column to equal the total number of docking ports in between each segment of your craft - not including any docking port on the end.

Can you confirm if this is working the same way for you if you just add a few more blank stages to the column? I would add this to the bug tracker, but my game is heavily modded and the new update is releasing soon anyway. I'll try to reproduce this bug in an unmodded 1.9 game when it comes out before reporting it.

(edit to add: The problem seems to be caused when any engine plate is staged with the space bar OR an engine plate has its staging deactivated in the VAB. I was able to reproduce the problem with non-nuclear engines as well as long as there was a combination of engine plate + docking ports. Otherwise identical configurations worked perfectly normally if all I did was remove the engine plate from the design.)

Edited January 28, 2020 by HvP

[OHara]

There are some similar existing bug-reports.
Very similar https://bugs.kerbalspaceprogram.com/issues/20926 was thought to be fixed, but maybe not completely.
https://bugs.kerbalspaceprogram.com/issues/20740 is about decouplers making dV wrong by a factor.
And others that match less well.

Sounds like save/reload is a workaround. 
There is also a suggestion to remove the (sometimes confusing) decoupler function from the engine plates, https://bugs.kerbalspaceprogram.com/issues/21143 with an attached module manager patch that removes the decoupling function entirely, so might avoid this problem in future builds.  The idea is to add an explicit decoupler beneath the engine plate. (The engine plate costs and weighs so little, it seems only fair to pay for a separate decoupler part.)

 

 

[maphi100]

@HvP Wow, this works perfectly. Thanks a lot man, you delivered a great explanation on why this bug occurs and how it's fixed. Great help! 

[Krazy_Kerbal]

Thank you for the fix! Surprised this still hasn't been addressed, but it looks like the devs have moved on to KSP2 (where I personally hope it gets fixed). Cheers!