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Odd body-force-vector(s) Orbiter-BETA Issue Tools
issueid=1402 03-05-2019 06:49 PM
Donator
Odd body-force-vector(s) Orbiter-BETA
Display of body-force vectors is "odd"

I've noticed an issue with r86 (and r87 as well).
The body-force-vectors (torque in particular) is/are displayed oddly...

I've checked r86 and r87, but it could have been in there before

(See attachment)
Issue Details
Project ORBITER: 2010-P1 and newer
Status Awaiting Feedback
Priority 9
Affected Version Revision denoted in description
Fixed Version (none)
Users able to reproduce bug 0
Users unable to reproduce bug 0
Assigned Users (none)
Tags (none)

03-05-2019 07:04 PM
GLS GLS is offline
Addon Developer
 
This is present in r85.
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03-06-2019 07:37 PM
Donator
 
I did a little bit of "time travel" down the repository history and it seems that the odd vectors first appeared in r14 !!
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03-06-2019 09:05 PM
Beta Tester
 
Are you reffering to sudden changes (oscullations) in torque ?
Could it be some kind of dampping ? Liquid fuel in the tanks. I don't think Orbiter goes that far. But I wouldn't be shocked if it did.


EDIT: Sorry didn't notice the screen shot. Yes, there is some odd behavior there.
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03-07-2019 11:36 AM
Orbiter Founder
 
Actually, the force vectors shown in the image don't look like torques, but like (linear) friction forces at the touchdown points.

I implemented those as a quick hack at some stage when working on vessel-surface interactions. They are currently undocumented (sorry!) and there is no UI element to switch their display individually, so they are always shown when body forces are shown. I could add a checkbox for them, or alternatively drop them altogether, if they are confusing or uninformative.

Regarding the image itself, the DG forces shown could be down to Coriolis forces, or the DG is standing on a slope, although the magnitude looks a bit large in either case. I'll have to check that. Also, the vector origins look slightly displaced from the touchdown points.

Not sure what's going on with the Shuttle-A though. Does this settle down after a few frames? It may be that at simulation start, while the vessels settle into an equilibrium state there may be some spurious forces showing, but this should eventually disappear.

Edit: also, if the vessels are in landed (idle) state at simulation start, it may be that the friction forces are initialised in an unstable vessel state and then never updated, since idle vessels only do a limited physics cycle. In that case, forcing the vessel to active (apply momentary tiny thrust) should fix the state. Does that happen?
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03-07-2019 08:33 PM
Donator
 
Quote:
Originally Posted by martins
 Actually, the force vectors shown in the image don't look like torques, but like (linear) friction forces at the touchdown points.

I implemented those as a quick hack at some stage when working on vessel-surface interactions. They are currently undocumented (sorry!) and there is no UI element to switch their display individually, so they are always shown when body forces are shown.
Yeah, that was my impression too (after a while). I think I was mostly confused with
a) them being not having their origin at CG
b) them being "affected" by the torque checkbox

Quote:
Originally Posted by martins
 I could add a checkbox for them, or alternatively drop them altogether, if they are confusing or uninformative.
I think they could be quite useful, now that we know what they are
A separate checkbox might be needed for it to be "logical".
A couple of API methods / definitions are needed, too (VESSEL::GetXxxVector() and bfvflag Bit flags) but I'm sure you know that.
If however some more important things need your attention first, I would suggest to completely disable them - temporarily.

Quote:
Originally Posted by martins
 Not sure what's going on with the Shuttle-A though. Does this settle down after a few frames?
No, that huge vector is pretty stable.

Quote:
Originally Posted by martins
 [...]In that case, forcing the vessel to active (apply momentary tiny thrust) should fix the state. Does that happen?
I'll try and report back.
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03-07-2019 08:38 PM
Donator
 
Forcing the vessel to active (by applying momentary tiny thrust) did change the Shuttle-A friction force vectors quite dramatically.
Still "wobbly" a while, but the magnitudes are way more reasonable after that.
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03-07-2019 08:54 PM
Donator
 
Regarding API changes:
The D3D9Client currently uses a hooking strategy to get the information that is not provided through the API (see OapiExtension(D3D9Client).zip ).
So if you add a new checkbox it would be nice if those IDC_xxx values would be the same...
An official API support (callbacks etc.) would be perfect, but to keep workload minimal and minimize incompatibilities it would be good to keep the IDC_xxx values.

For the midterm progress it seems that option "disable them in inline GC" would be the simplest solution, though
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