Strange Kerbal Engineer reading

[Gilead]

Hi!

I'm trying to send a rover to the Mun, but Kerbal Engineer gives strange readings on my launcher !

Here's my launcher

I have a poodle engine on S2 with a full fuel tank, and yet it says S2 has 0 dV. And S0 is my rover and Kerbal Engineer says it has 3771 m/s dV?

Is something wrong with my ship or is Kerbal engineer bugging? At game launch, the mod tells me it's for KSP 1.3, is that the problem? Apparently it's supposed to work fine on 1.4.

Edited May 14, 2018 by Gilead

[4x4cheesecake]

There is a fork of KER for KSP 1.4+ by jrbudda, you might want ot try this one: https://github.com/jrbudda/KerbalEngineer/releases

Edited May 14, 2018 by 4x4cheesecake

[Gilead]

Thx! I installed the last update of KER, but the readings are the same.

I'm gonna launch the vehicle anyway, I might see where the problem is that way.

 

EDIT : The ship works fine, S2 has access to the fuel and works as intended, but KER tells me it has 0m/s dV and 0 TWR...

Edited May 14, 2018 by Gilead

[4x4cheesecake]

Do you have an engine as root part? KER can be confused when building a rocket "from bottom to top"

[Gilead]

The root is the RC-L01 Remote Guidance Unit.

I tried rebuilding the ship from scratch. The readings are normal (3859m/s dV on the Poodle stage) until I add the rover on the radial decoupler on top, then, I get the same readings with the dV on the wrong stage...

So, I thought, maybe it's because of the rover root part? It is the central structural part, but if I use its probe core, it won't attach to the decoupler...

What's also weird is that in the VAB, my poodle stage has 1.79 TWR according to KER, but in flight KER says 0 TWR...

I'm lost.

[4x4cheesecake]

8 minutes ago, Gilead said:

I'm lost.

Well, me too, pretty strange behaviour. Maybe @jrbudda knows more about it.

[Gilead]

It was a root problem! I re-rooted the ship and selected the rover's probe as the root instead of the launcher's probe, and the readings are normal.

Edited May 14, 2018 by Gilead

[4x4cheesecake]

4 minutes ago, Gilead said:

It was a root problem! I re-rooted the ship and selected the rover's probe as the root instead of the launcher's probe, and the reading are normal.

Glad to hear it's working now but still pretty strange. Would be nice to know if this is a KSP problem or a KER problem.

Edited May 14, 2018 by 4x4cheesecake

[Gargamel]

9 hours ago, 4x4cheesecake said:

Would be nice to know if this is a KSP problem or a KER problem.

I don't see how it could be a KSP problem.  KSP has nothing towards giving dV readouts,  so it just is what it is.  KER would have to learn to work around any weirdness the stock game is having.   Not saying it's not KSP's fault, but the onus is on KER to know how to handle it. 

[4x4cheesecake]

2 minutes ago, Gargamel said:

I don't see how it could be a KSP problem.  KSP has nothing towards giving dV readouts,  so it just is what it is.  KER would have to learn to work around any weirdness the stock game is having.   Not saying it's not KSP's fault, but the onus is on KER to know how to handle it. 

Calculating the dV requires two things: 1) The informations about wet/dry mass, engine isp, gravity and 2) something to put these values into an equation. (AFAIK) the KSP API provides the informations, KER calculates everything and it is totally possible that bugs can happen on both sides as soon as some weird root stuff is going on.

It's just a thought, but maybe it is possible that the API cannot provide correct (er even any numbers) as soon as the root part is switching around the vessel. Wouldn't be the first time that errors occures during a reroot process (at least for me).

[Gargamel]

22 minutes ago, 4x4cheesecake said:

Calculating the dV requires two things: 1) The informations about wet/dry mass, engine isp, gravity and 2) something to put these values into an equation. (AFAIK) the KSP API provides the informations, KER calculates everything and it is totally possible that bugs can happen on both sides as soon as some weird root stuff is going on.

It's just a thought, but maybe it is possible that the API cannot provide correct (er even any numbers) as soon as the root part is switching around the vessel. Wouldn't be the first time that errors occures during a reroot process (at least for me).

True.... but until it is causing issues in the stock game, it is just a behavior, not a problem...  *shrug*

[Gilead]

Hi, people, I asked about it on the KER thread, and jrbudda explained it. It is normal behavior after all.

His words:

Quote

Yup, totally normal. S0 is not the rover if the probe core is the root, its the probe core. KER is telling you when you activate your last stage, the dead weight of the rover is left behind and the core, tank, and poodle now have lots of dV.

So now we know.