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| | | |-+  SCS stuff committed...
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Author Topic: SCS stuff committed...  (Read 14482 times)
Christophe
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« Reply #60 on: October 01, 2006, 04:35:38 AM »

I read the same astronauts complains somewhere, but in this case, the SCS seems to overpower the attitude correction: I saw about 0.5/sec rate which is very high.
You can manually readjust the desired attitude and damp the rates but as soon as the vessel go a little off the attitude, things go wrong again.
I tried with single jet operation (yaw and pitch axis) but that doesn't solve the issue.
For my own, I don't see any noticeable difference wether the lim cycle is on or off.
No matter... we just have to learn to fly that damn bird as it is!

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dseagrav
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« Reply #61 on: October 01, 2006, 04:55:02 AM »

.5 dps could be normal depending on the mode and axis.

With the switch in HI RATE, the maximum proportional-rate commands are 20 dps in roll and 7 dps in pitch and yaw.
Low rate gets you .7 dps in all axes. For rate-damping mode it commands 2 dps (hi rate) and .2 dps (lo rate) in all axes.

I'd take a look at it but my code is very out-of-sync right now. I'm still working at getting optics to correctly issue commands. I've been in AGC manuals for the past couple weeks figuring out how the interface worked at the physical level to try and figure out what exactly the computer is expecting to happen. I want to get it solved before I try to upgrade Orbiter and resynchronize, because that's potential disaster and I really don't want to lose my place.

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Tschachim
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« Reply #62 on: October 01, 2006, 06:15:48 AM »

Hi dseagrav,

can you explain what the limit cycle "pseudo rate feedback" does (or should do) ?

Cheers
Tschachim
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dseagrav
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« Reply #63 on: October 01, 2006, 03:34:31 PM »

It sounds more complicated than it is. It causes jet commands to generate pseudo-rate in the direction they fire. Basically if a jet is being commanded to fire, a small amount of additional (pseudo) rate is generated in the direction of the jet. This causes the jet to pulse off and on when it gets close to the edges of the deadband, which is supposed to save fuel and reduce the ship's tendency to bounce back and forth between the edges of the deadband.
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Tschachim
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« Reply #64 on: October 05, 2006, 11:24:25 AM »

Hi dseagrav & Christophe,

I reviewed the SCS attitude hold mode and the limit cycle stuff the last days, read the AOH again and I think the commanded rates during attitude hold mode were wrong. I changed that already in CVS, but I'm not sure if I'm right so I would like to discuss that:

Basically the commanded rates during attitude hold mode aren't a fixed value but depends on the attitude error. Especially with low rate and min attitude deadband the commanded rate is the attitude error, in opposite direction, of course (AOH SCS pdf, pg. 33). You get the 0.2 attitude deadband automatically because this is the rate deadband. At high rate the rate deadband is 2, the commanded rate is half of the attitude error, so the 4 deadband is accomplished (or the 1:20 scaling with respect to low rate as mentioned in the AOH). With max attitude deadband the first 4 attitude error are subtracted, so you get the 4.2/8 attitude deadband.

With this change attitude hold works much better now, especially for pitch and yaw, it still "oscillates" after a perturbation until the attitude to hold is archived, but not forever anymore.

I'm still not sure if I understand the pseudo rate feedback correctly, I didn't find much information about it, additionally to the AOH some informations are here: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19670007177_1967007177.pdf But as mentioned by dseagrav basically it pulses the thrusters by applying an increasing "fake" rate to the commanded rate if a thruster is firing, and decreasing this rate again if the thruster stops firing. I changed the code in accordance with that, the old code seemed to do (almost) nothing, at least no thruster pulsing. With that change the attitude rates generated by the attitude hold commands are smaller as described in the AOH, but I'm not sure if my implementation is really correct.

... and the the pseudo rate feedback is applied only if you are in RATE CMD mode (additionally to limit cycle to on), I changed that, too.

I would be happy if you can take a look at the changes and do some tests, I hope it's working better now. Happy

Cheers
Tschachim
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Christophe
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« Reply #65 on: October 06, 2006, 04:46:27 AM »

Hi Tschachim.
I'm pretty sure things will go far better now.
I got heavy troubles with my Pc and my internet connection actually so it's a pain to download cvs. I'll try it ASAP.
Thanks.
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Swatch
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« Reply #66 on: December 19, 2007, 04:19:12 AM »

This is directed at dseagrav....

What are the units for the rates variable in the GDC code?

Code:
sat->gdc.rates.y

This is the variable I want to know about.
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My Project Apollo Work:
CM Visual
 -VC (~75% complete: texture work beginning again; mesh-78%; texture-70%)
Propulsion Particle Improvements (Focused on S1B right now, BETA 1.0 has been commited)
New Docking Method (~50% complete: research complete; coding partially completed, testing not underway)

Future Work:  (if it's here, it's deemed unnecessary to upcoming release)

Older Work:  (if it's here, it's fair game to whoever wants to improve)
EMS Implementation (committed: minor flaws, but groundwork is there, needs extensive testing)
EMS scrolls (committed: not refined, but usable)
SM Visual (committed: mesh-finished, texture-60%; possibly revisited in future)
J2 Texture (commited: room for improvement)
LRV (committed: mesh-finished, texture-90%; in future a ground up rebuild may be in order, but not on my plans)
Tschachim
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« Reply #67 on: December 19, 2007, 08:53:28 AM »

That should be radian/second.

Cheers
Tschachim
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Swatch
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« Reply #68 on: December 19, 2007, 10:58:15 AM »

That's what I figured it was, but I wasn't 100% sure. Thanks!
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My Project Apollo Work:
CM Visual
 -VC (~75% complete: texture work beginning again; mesh-78%; texture-70%)
Propulsion Particle Improvements (Focused on S1B right now, BETA 1.0 has been commited)
New Docking Method (~50% complete: research complete; coding partially completed, testing not underway)

Future Work:  (if it's here, it's deemed unnecessary to upcoming release)

Older Work:  (if it's here, it's fair game to whoever wants to improve)
EMS Implementation (committed: minor flaws, but groundwork is there, needs extensive testing)
EMS scrolls (committed: not refined, but usable)
SM Visual (committed: mesh-finished, texture-60%; possibly revisited in future)
J2 Texture (commited: room for improvement)
LRV (committed: mesh-finished, texture-90%; in future a ground up rebuild may be in order, but not on my plans)
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