Problem [partially resolved] Contact Points with VesselBuilder

[jacquesmomo]

Hi every body

So I can't find the solution...
Generally I am capable of spending hours to find the solution to my problem (and thus learn) but I have already spent a lot of time and I cannot find it.

So if anyone can help me...

Here is my problem:

I would like to update my Tintin on the Moon addon for Orbiter 2016 using Fred's VesselBuilder which I think I know well by now...

But I stumble on the points of contact.

Here is what I have, even if in the TDP values I put a value for Y = -23
(I tried with 0, -50, -10...always the same position (height relative to the ground) !!!



Of course I could "lift" the mesh (I tried with MESH_0_POS = 0 23.5 0) but the CG is no longer where I would like: it is too low whereas I would like it to be approximately at the level of the hold door.



I think I put for EMPTY_MASS = 50000

So if someone can solve my problem, not only will I be grateful to them for eternity, but above all their name will be on the doc next to Dr. Martin and Fred18!!!!


And also... any idea for these values?

Here is dimensions of the meshe :



EMPTY_MASS = 50000 (modifiable value but for this rocket it seems realistic to me, right?)
VSIZE = < I have no problem there >
PMI = ? ? ?
CSECTIONS = ? ? ?
GRAVITYGDAMP = 0 (it seems reasonable to me to leave the value "0")
ROTDRAG = ? ? ?

But above all:

TDP_1_0_POS =
TDP_1_0_STIFFNESS =
TDP_1_0_DAMPING =
TDP_1_0_MU =
TDP_1_0_MULNG =

TDP_1_1_POS =
TDP_1_1_STIFFNESS =
TDP_1_1_DAMPING =
TDP_1_1_MU =
TDP_1_1_MULNG =

TDP_1_2_POS =
TDP_1_2_STIFFNESS =
TDP_1_2_DAMPING =
TDP_1_2_MU =
TDP_1_2_MULNG =

(afterwards there will remain the Contact Points for the top ( TDP_3_ 4 etc...) but it's less important... for the moment

So if you have the solution.... thank you in advance!!!

 

[N_Molson]

I'm not sure, but keep in mind that Orbiter 2016 simulates spring/damping*. The values "Stiffness, damping..." refer to the spring simulation. My hypothesis is that you might have spring values designed for a much lighter vessel (like the ShuttlePB, often used as a "default"), and that adding 50 tons of mass litterally stick the center of mass to the ground. Imagine you add 50 tons (in short, a Leclerc MBT) on the roof of a Renault Clio car... I think the chassis would pretty much stick to the parking (and I'd prefer not to be inside the poor car!) Now maybe it is something else!

* in French : suspension

 

[nbcfrosty]

Hey there. You can use shipedit to find some of your values. Example:


The PMI is the diagonal of the intertia tensor.
As for touchdown points, here's a heuristic that works for me for tail landers:

VECTOR3 pt1, pt2, pt3;
double size = stage.diameter;

pt1 = _V(0, size, -stage.height);
pt2 = _V(size, 0, -stage.height);
pt3 = _V(-size, 0, -stage.height);
VECTOR3 p4 = _V(0, 0, 1);
    
const DWORD ntdvtx_geardown = 4;
TOUCHDOWNVTX tdvtx_geardown[ntdvtx_geardown] = {
        {_V(p1.x, p1.y, p1.z - padbias), 1e8, 1e6, 3, 1},
        {_V(p2.x, p2.y, p2.z - padbias), 1e8, 1e6, 3, 1},
        {_V(p3.x, p3.y, p3.z - padbias), 1e8, 1e6, 3, 1},
        {p4, 1e8, 1e6, 3},
};
SetTouchdownPoints(tdvtx_geardown, ntdvtx_geardown);

 

[BrianJ]

Hi Jacques,
is the vessel already landed in your test scenario?
If the vessel is already landed, I think the height above ground is set by the scenario ALT value.
So changing the contact points has no effect (until you apply a enough thrust to get airborne).
(....I think that is correct )
Could be the problem?
Cheers,
BrianJ

 

[jedidia]

Yeah, on seeing this, my first suspicions are "spring compression" and "might jump to the moon as soon as you touch a thruster". Because that's what happens with a vessel that is loaded in a landed state that results in uber-compressed springs of the touchdown points. It gets catapulted to oblivion by a mathematical anomaly as soon as landed state is canceled and the springs are allowed to apply force to the vessel while being in a state that wouldn't be physically possible...

 

[jacquesmomo]

First of all, thank you for your answers

@N_Molson :
Of course you are right....
The moon rocket is not a clio.... Professor Calculus will be upset !
But I tried with different stiffness/damping values, it doesn't work....with MASS = 50000

@nbfrosty :
Yes, I used Shipedit but forgot about PMI...
(we quickly forget at my age!) so thank you for this reminder.

I'm going to try the values you suggest, but I think I've already used this kind of values without success...

@BrianJ
Regarding ALT, I discovered this while doing my "Guyane Airport" add-on (and AROT too which - I think - has priority over ALT)

Here is my SCN :
BEGIN_SHIPS
Fusee-Lunaire:Tintin_VB\VB_Fusee-Lunaire
STATUS Landed Earth
POS -52.3279330 4.8190804
HEADING 0
FUEL 1
AFCMODE 7
NAVFREQ 0 0
END
END_SHIPS

So I didn't put ALT and of course I make every time a few meters lift off to see how the rocket is going to land....

I looked through your ccp files to find the values you use for the SpaceX rocket's first stage when it lands.
but I haven't found it yet... (I'm starting to read these files to understand, but I haven't started spawning dlls yet...)
(Thanks to roof my VC++ works, and when I start using this method, I will certainly have hundreds of questions to ask you!!!)

Could you give me your values to try (with the weight you use) ?

@jedidia :
Yes, I saw that it's not easy, because once I have managed to adjust the contact points for the Earth, it also has to work for the Moon...


@For all :
I understand that the weight I use (50,000) is very (too?) high.
If I put 1000 it's easier to adjust.
But is this realistic for such a rocket?

For comparison, for my French Guiana add-on, I set the following values for the weight:
For the characters:
EMPTY_MASS = 1000
PRP_0_MAXMASS = 1000
So 2000 kg is a lot for a human, but lighter it doesn't work!!!

And for my Cessna :
EMPTY_MASS = 5000
PRP_0_MAXMASS = 400
while a CESSNA weighs (empty) is 757 kg...

So I think the only solution I have is to set a much lighter weight for my rocket ?

What do you think of that ?
If there is no other solution I will try this, but I wanted to get your opinion before....

(and sorry for my bad english...)

 

[BrianJ]

Hi Jacques,
here are the values I use for Falcon9 booster stage.....

Falcon9 booster empty mass = 22200kg
STIFFNESS = 1e6
DAMPING = 1e6
MU = 2
MULNG = 2

....every time a few meters lift off to see how the rocket is going to land....

OK, good.

Can you post the actual code you are using? There may be a small error (typo) somewhere that is causing VesselBuilder to fail to load the contact point values.

Cheers,
BrianJ

 

[N_Molson]

@jacquesmomo : finding the right values isn't easy at all... And the equations behind the spring system are not trivial. What we need is some kind of calculator that could compute the values for us. If someone good-at-maths and physics is interested... It would make things much easier!

The Falcon9 values will do the job. I think Tintin's rocket has some spring system into the "feet", but there is no details on how it works in the story.

About the mass : the rocket should be quite heavy. It is massive, and the "atomic engine" can't be very light (radiation shielding...)

 

[jacquesmomo]

Hi BrianJ, Hi everybody

@BrianJ :
I test your values... same !



Values from Shipedit.exe :

And here are the lines in the VesselBuilder cfg file :

;<-------------------------GENERAL SETTINGS - Configuration: 0------------------------->
 
EMPTY_MASS = 22200
VSIZE = 3
PMI = 200 55 200
CSECTIONS = 400 98 475
GRAVITYGDAMP = 0
ROTDRAG = 10 10 10
 
;<-------------------------MESHES DEFINITIONS------------------------->
 
MESH_0_NAME = Tintin_VB\Fusee_lunaire
MESH_0_POS = 0 0 0
MESH_0_DIR = 0 0 1
MESH_0_ROT = 0 1 0
MESH_0_VIS = 1
 
;<-------------------------DOCKS DEFINITIONS------------------------->
 
 ;<-------------------------ATTACHMENTS DEFINITIONS------------------------->
 
;<-------------------------ANIMATIONS DEFINITIONS------------------------->
 
;<-------------------------PROPELLANT DEFINITIONS------------------------->
 
PRP_0_ID = 0
PRP_0_MAXMASS = 1000
PRP_0_EFFICIENCY = 1
PRP_0_PRIMARY = TRUE
PRP_0_NAME = Tournesolite

;<-------------------------TOUCHDOWNPOINTS DEFINITIONS------------------------->
 
TDP_1_0_POS = 0 -23 11
TDP_1_0_STIFFNESS = 1000000
TDP_1_0_DAMPING = 1000000
TDP_1_0_MU = 2
TDP_1_0_MULNG = 2
 
TDP_1_1_POS = -9.5 -23 -5.5
TDP_1_1_STIFFNESS = 1000000
TDP_1_1_DAMPING = 1000000
TDP_1_1_MU = 2
TDP_1_1_MULNG = 2
 
TDP_1_2_POS = 9.5 -23 -5.5
TDP_1_2_STIFFNESS = 1000000
TDP_1_2_DAMPING = 1000000
TDP_1_2_MU = 2
TDP_1_2_MULNG = 2

Something strange : I've tried -33 then -50 for the Y POS (TDP_1_0_POS to TDP_1_2_POS) and the rocket is landig same, under the ground... not higher, not lower.
Stange, no ? I tried too with EMPTY_MASS = 2220 instead of 22200... same !!!
Something I don't understand....

Just as a reminder, the values that I used for Orbiter 2010 (Spacecraft3 rocket) were :

[CONFIG]
MESHNAME="Tintin\Fusee_lunaire"
SIZE = 50
EMPTY_MASS = 40000
FUEL_MASS = 50000
ISP = 3e5
MAIN_THRUST = 8e6
RETRO_THRUST = 1e6
HOVER_THRUST = 0
ATTITUDE_THRUST = 500000
PMI=(340,350,100)
CROSS_SECTION=(701,608,141)
CW_Z_POS=0.08
CW_Z_NEG=0.08
CW_X=0.3
CW_Y=0.3
COG=0
PITCH_MOMENT_SCALE=0.1
BANK_MOMENT_SCALE=0.1
ROT_DRAG=(10,10,10)
LAUNCH_PT1=(6,-10,-26.2)
LAUNCH_PT2=(-11.6,15,-26.2)
LAUNCH_PT3=(6,10,-26.2)
LAND_PT1=(266,-270,-26.2)
LAND_PT2=(-271.6,275,-26.2)
LAND_PT3=(266,270,-26.2)
VISIBLE=1
CAMERA=(0,0,28)
FOCUS=-1

If I can't solve this problem, I will raise the mesh 23 meters higher...
But I would like to understand why this problem....

@N_Molson
Regarding the atomic engine, it is difficult to know the weight...
And what about the famous Calculus's calculon (tournesolite in french) product which is still a secret...

In fact I based myself on the characteristics of Saturne 5 :
Weight 2,900,000 kg
height 110 m
So I put (for the "spacecraft3" model) :
EMPTY_MASS = 40000
FUEL_MASS = 50000
so almost 100,000 kg for a height of 55 meters.
We are far from the real weight of half a Saturn 5 rocket !!!
This works fine for "spacraft3" and Orbiter 2010, but not for "VesselBuilder" and Orbiter 2016...

WHY ????

 

[nbcfrosty]

This is crude but works reasonably well for me:

        double size = 40;
        double height = 26;
        p1 = _V(0, size, -height);
        p2 = _V(size, 0, -height);
        p3 = _V(-size, 0, -height);
        VECTOR3 p4 = _V(0, 0, 1);

        const DWORD ntdvtx_geardown = 4;
        TOUCHDOWNVTX tdvtx_geardown[ntdvtx_geardown] = {
                {_V(p1.x, p1.y, p1.z), 1e8, 1e6, 3, 1},
                {_V(p2.x, p2.y, p2.z), 1e8, 1e6, 3, 1},
                {_V(p3.x, p3.y, p3.z), 1e8, 1e6, 3, 1},
                {p4, 1e8, 1e6, 3},
        };
        v->SetTouchdownPoints(tdvtx_geardown, ntdvtx_geardown);

It's relatively stable when landing, especially with the Parking Brake MFD.

 

[BrianJ]

Hi Jacques,
since I have not used VesselBuilder I don't think I can help very much, but here is a couple of thoughts for you......

1. The example vessel .cfg's in VesselBuilder package all use at least 4 contact points - try adding a 4th point.
2. Check that the .cfg you are modifying is actually the correct one! (I have made this mistake before)

Also, I don't understand how these parameters work...

MESH_0_DIR = 0 0 1
MESH_0_ROT = 0 1 0

The values are obviously not angles.
Your vessel is oriented along Y axis, unlike the "Jarvis" example in VesselBuilder package - does that make any difference?

OK, good luck!
BrianJ

 

[jacquesmomo]

@BrianJ
Yes, you are right, but the 4th point is only used for another point of contact of the mesh, such as the top.
The base, what defines the contact points (like for a vehicle or an airplane) are the first 3.
Of course we can put more than 4, but it's the first 3 that are important.

Regarding the orientation of the rocket mesh:
I wanted to orient it with the Y upwards (like the LEM) to facilitate landing on the moon but especially on earth. (with the hoovers)

But I realize that MFDs (especially orbit MFDs) are not intended for this configuration.
I therefore have to make my mesh with the rocket directed with the Z axis upwards (like all rockets....), otherwise it is not controllable.

Vesselbuilder allows you to change the thrust axes of the "HOOVER"
So I set it with the same axis as "MAIN"...
And this allows the "HORZ LVL" and "HOLD ALT" commands to work.

Concerning the contact points, I gave up on the idea of putting the CG (XYZ=0 of the mesh) in the middle of the height of the rocket body.
By putting the CG (or XYZ=0 of the mesh) at ground level (bottom of the mesh) and moving the mesh up in the vesselbuilder cfg file, it works.

And finaly for contact points I put this:

TDP_1_0_POS = 9.5 -5.5 -1
TDP_1_0_STIFFNESS = 1000000
TDP_1_0_DAMPING = 300000
TDP_1_0_MU = 1
TDP_1_0_MULNG = 1
 
TDP_1_1_POS = -9.5 -5.5 -1
TDP_1_1_STIFFNESS = 1000000
TDP_1_1_DAMPING = 300000
TDP_1_1_MU = 1
TDP_1_1_MULNG = 1
 
TDP_1_2_POS = 0 11 -1
TDP_1_2_STIFFNESS = 1000000
TDP_1_2_DAMPING = 300000
TDP_1_2_MU = 1
TDP_1_2_MULNG = 1
 
TDP_1_3_POS = 0 0 50
TDP_1_3_STIFFNESS = 100000
TDP_1_3_DAMPING = 3000
TDP_1_3_MU = 1
TDP_1_3_MULNG = 1

with

EMPTY_MASS = 50000
MESH_0_POS = 0 0 25

Now I'm going to try to adjust all of this better, and see what that gives in terms of piloting.

I will only take care of the look of the rocket and the animations if it is pilotable....

Thank you all for your help !!!!

 

[jacquesmomo]

Oh... I've forgoten...

Regarding these two parameters ( MESH_0_DIR = 0 0 1 and MESH_0_ROT = 0 1 0)
they allow you to position the mesh used.

For example if we put
MESH_0_DIR = 0 0 1
MESH_0_ROT = 0 -1 0
head will be down

and if we put
MESH_0_DIR = 0 0 -1
MESH_0_ROT = 0 1 0
the back will be directed forward...

 

[BrianJ]

I just did some experiments with VesselBuilder.

This works for me (vessel empty mass 22200, no propellant):

TDP_1_0_POS = 0 -28 11
TDP_1_0_STIFFNESS = 1000000
TDP_1_0_DAMPING = 1000000
TDP_1_0_MU = 2
TDP_1_0_MULNG = 2
 
TDP_1_1_POS = -9.5 -28 -5.5
TDP_1_1_STIFFNESS = 1000000
TDP_1_1_DAMPING = 1000000
TDP_1_1_MU = 2
TDP_1_1_MULNG = 2

TDP_1_2_POS = 9.5 -28 -5.5
TDP_1_2_STIFFNESS = 1000000
TDP_1_2_DAMPING = 1000000
TDP_1_2_MU = 2
TDP_1_2_MULNG = 2

TDP_1_3_POS = 0 30 0
TDP_1_3_STIFFNESS = 1000000
TDP_1_3_DAMPING = 1000000
TDP_1_3_MU = 3
TDP_1_3_MULNG = 0.2

......but this does NOT work.....

TDP_1_0_POS = 0 -28 11
TDP_1_0_STIFFNESS = 1000000
TDP_1_0_DAMPING = 1000000
TDP_1_0_MU = 2
TDP_1_0_MULNG = 2
 
TDP_1_1_POS = -9.5 -28 -5.5
TDP_1_1_STIFFNESS = 1000000
TDP_1_1_DAMPING = 1000000
TDP_1_1_MU = 2
TDP_1_1_MULNG = 2

TDP_1_2_POS = 9.5 -28 -5.5
TDP_1_2_STIFFNESS = 1000000
TDP_1_2_DAMPING = 1000000
TDP_1_2_MU = 2
TDP_1_2_MULNG = 2

So it seems you need minimum 4 contact points.....
And the first 3 points must be in the correct order: Front(+Z), Left(-X), Right(+X) as usual.

 

[N_Molson]

So it seems you need minimum 4 contact points.....
And the first 3 points must be in the correct order: Front(+Z), Left(-X), Right(+X) as usual.

Yes in Orbiter 2016 you have to define a minimum of 4 points, because those 4 points define a collision mesh that is computed against terrain elevation. The tetrahedron (aka "3 faces pyramid") is the simplest 3D shape possible :

Now in this specific case of Tintin's rocket, things are rather easy : the first 3 points should define the feet of the 3 legs, and the 4th should define the tip of the rocket. The collision box of Tintin's rocket actually is a terahedron. A ; B ; C are the first 3 points while D is the 4th one (and ideally should have different friction/spring parameters, but that's not absolutely necessary).

 

[jacquesmomo]

Thanks again for looking for a solution for me...

So, as I explained before, I put the rocket with the Z axis facing up. (not as a Dg or a Lem, but like a rocket)

So I took your values, and here is what I get:

That way, madness lies!

I tried many combinations, with 4 or more points, and the best I could do is this:

TDP_1_0_POS = 9.5 -5.5 -1
TDP_1_0_STIFFNESS = 1000000
TDP_1_0_DAMPING = 300000
TDP_1_0_MU = 2
TDP_1_0_MULNG = 2
 
TDP_1_1_POS = -9.5 -5.5 -1
TDP_1_1_STIFFNESS = 1000000
TDP_1_1_DAMPING = 300000
TDP_1_1_MU = 2
TDP_1_1_MULNG = 2
 
TDP_1_2_POS = 0 11 -1
TDP_1_2_STIFFNESS = 1000000
TDP_1_2_DAMPING = 300000
TDP_1_2_MU = 2
TDP_1_2_MULNG = 2
 
TDP_1_3_POS = 0 0 50
TDP_1_3_STIFFNESS = 1000000
TDP_1_3_DAMPING = 100000
TDP_1_3_MU = 10
TDP_1_3_MULNG = 10

and with

EMPTY_MASS = 50000
PRP_0_MAXMASS = 1000

and with the mesh moved up

MESH_0_POS = 0 0 25

If I put -20 instead of -1 for the height, it doesn't work....

Odd thing: I wanted to show you the video...
I use FRAPS and as soon as I open it with Orbiter, the rocket wobbles and ends up falling....
Another weird thing...

Either my computer is haunted, or it is mad at me...

I think I'll take a break otherwise I'll go crazy...
And maybe I will keep these values....

 

[N_Molson]

I'd say go back to the basics, and proceed step by step. Be sure you know what you are doing when you modify values, else things will add up and in the end make no sense.

As an example you should not temper with the meshpos value at this stage. Your mesh looks correctly centered, so there's no reason to change that. You need to understand better the way Orbiter 2016 handles touchdown points collision boxes. In Orbiter 2010 it was bi-dimensional (2D footprint), in 2016 it is tri-dimensional (3D collision box). The complex but accurate spring system requires spending some time understanding how it works (the basics).

The fact you have to use "wrong" mass values to get it working is a red flag, it has to be solved first. Orbiter is a simulation so using real values isn't an option.

 

[jacquesmomo]

I'd say go back to the basics, and proceed step by step. Be sure you know what you are doing when you modify values, else things will add up and in the end make no sense.

That's how I understand things, but adjusting the contact points is still complicated: each modified value influences the others...

The complex but accurate spring system requires spending some time understanding how it works (the basics).

Absolutely !

The fact you have to use "wrong" mass values to get it working is a red flag, it has to be solved first. Orbiter is a simulation so using real values isn't an option.

I understood this with my Guyane-airport add-on (the Cessna and the characters)
But this is confirmed with my tests on Tintin's rocket.
The mass must indeed be modified, but I also think that the values of the contact points must be adapted to the CG of the mesh:
if I modify the value of Y from -1 to -5 it works, at -10 there is already a problem, at -25 it no longer works...

Anyway, that's how I learn...


So I'm going to think about it and start again from the beginning.

The solution might be for me to take the next step: learn how to code a dll...
But then I haven't finished boring BrianJ with hundreds of questions...

I'll see later....

Thanks again to everyone !

 

[BrianJ]

Hi Jacques,
I hope you can find a solution - "Destination Moon" and "Explorers on the Moon" are my favourite Tintin books ;-)

The solution might be for me to take the next step: learn how to code a dll...
But then I haven't finished boring BrianJ with hundreds of questions...

Whenever you are ready, mate!

Cheers,
Brian

 

[N_Molson]

The solution might be for me to take the next step: learn how to code a dll...

It isn't that hard, really. And from there you can do nearly everything you want. I can help you in French, no problem !