Project XR2 Ravenstar - Mk II

[markl316]

Yes, what you are seeing is normal. I'll try to explain exactly why here. Tuning an autopilot is a compromise between 1) Efficiency (how much RCS fuel does it burn?), 2) Stability (how stable and smooth is the ship under time acceleration [low effective frame rates]?), and 3) Tolerance (how tightly does it try to hold a given setting?). It is relatively simple to make an autopilot that is very good at any one of those three criteria. It is much more work, however, to build one that is pretty good at all three.

For example, it's easy to tune an autopilot for very tight tolerances (i.e., hold within 0.1 degree) if you crank up the RCS power it uses at every timestep. When you do that, however, two things happen: 1) efficiency goes way down because the autopilot is much more prone to "overshooting" and then correcting with almost the same force in the opposite direction due to the framerate varying and/or just being too low, and 2) stability would be terrible under time acceleration (i.e., low effective frame rates) because of the "overshooting" that would constantly occur as the hold targets/air density/framerate constantly varied. So the trick is to tweak the autopilot code to be efficient and stable even under low frame rates while still holding a good degree of accuracy. During testing and tuning I found that holding within 0.5 degree still allowed very good efficiency and stability, even under time acceleration. For example, if you're getting 40 fps or more you should be able to reenter using Attitude Hold even at 10x time acceleration, which is an effective framerate of only 4 frames per second. In other words, the XR's autopilot is only able to update thruster levels four times per second of simulation time while having to cope with constantly changing air resistance, hold targets, and framerate.

So it's really just a matter of design goals: in the XRs' case I wanted to be able to reenter at 10x time acceleration or more while Attitude Hold remained stable, so that's why I had to loosen the tolerance a little more than I would have liked. But the payoff was very good stability and efficiency.

Makes perfect sense, thanks for the explanation. I have noticed, reentering at 10x is not a problem. So is that why you made the descent hold autopilot so accurate, because nobody would be landing on the moon at 10x time acceleration?

What I am about to say, I am not trying at all to nitpick or nag you (you've done such a great job with this craft), but would it be difficult to incorporate a parameter in the config file, that allows the user to set the tolerance limit of the autopilot? If it would take much to long (such as rewriting the autopilot code), please don't worry about doing it, the Ravenstar is an amazing ship and this is one tiny detail that can easily be overlooked. I'm not a coder (MATLAB doesn't count :lol: ), so I wouldn't know how long something like this would take. Thanks for your feedback Doug.

 

[dbeachy1]

Makes perfect sense, thanks for the explanation. I have noticed, reentering at 10x is not a problem. So is that why you made the descent hold autopilot so accurate, because nobody would be landing on the moon at 10x time acceleration?

Well, you actually can auto-land on the moon using Descent Hold at 30x time acceleration provided you're getting a modest ~60 fps -- in other words, you can auto-land successfully at an effective framerate of only 2 frames-per-second. It is simply a matter of the Attitude Hold task being significantly more complex than the Descent Hold and Airspeed Hold tasks are.

What I am about to say, I am not trying at all to nitpick or nag you (you've done such a great job with this craft), but would it be difficult to incorporate a parameter in the config file, that allows the user to set the tolerance limit of the autopilot? If it would take much to long (such as rewriting the autopilot code), please don't worry about doing it, the Ravenstar is an amazing ship and this is one tiny detail that can easily be overlooked. I'm not a coder (MATLAB doesn't count :lol: ), so I wouldn't know how long something like this would take. Thanks for your feedback Doug.

No worries. However, TBH an option like that would cause more headaches than it's worth since it would compromise stability. Would you really be willing to wait thirty minutes during each reentry rather than three minutes because you had to give up 10x time acceleration just for the sake of going from a 0.5-degree pitch variance down to 0.2 degree? In any case, that option would require twice the testing and tuning as well, and so I would really rather not deal with that.

 

[markl316]

In any case, that option would require twice the testing and tuning as well, and so I would really rather not deal with that.

No worries, I don't want to stress you any more than you need, especially since this is freeware :thumbup:

And true, now that I think about it, waiting 30 minutes to reenter would get boring after a while...

 

[Keatah]

No worries, I don't want to stress you any more than you need, especially since this is freeware :thumbup:

And true, now that I think about it, waiting 30 minutes to reenter would get boring after a while...

Not if you do a stick and rudder seat-of-the-pants flight. From takeoff to landing, no autopilots, no instruments. Just airspeed and altitude. Look out the window to SEE where you are going. That's so cool!

 

[T.Neo]

Not sure if this is the place for it, but here is some more easter egg humor from Coolhand:

:rofl:

Anyone care to tell what it does?

 

[Xyon]

It's probably the button for the ejection seats... oh, wait... no it isn't...

 

[Foofoo14]

Are they going to add ejection seats?

 

[Xyon]

No. That was a joke, sorry.

 

[River Crab]

This might not belong here, but...
I wrote this free verse poem in awe of the XR2. The title actually means something else: http://tinyurl.com/2dgp7ho
I totally warped the assignment...got an A tho :lol:

Oh yeah, and the XR2 cockpit is hilarious. The only way it could be funnier is, when you press Esc 3 times, confetti blows out of the top hatch. :happybday:

 

[Dambuster]

This might not belong here, but...
I wrote this free verse poem in awe of the XR2. The title actually means something else: http://tinyurl.com/2dgp7ho
I totally warped the assignment...got an A tho :lol:

Oh yeah, and the XR2 cockpit is hilarious. The only way it could be funnier is, when you press Esc 3 times, confetti blows out of the top hatch. :happybday:

That poem is actually amazing! Well done!

 

[Izack]

I will never see a SCRAM ascent the same way again...

 

[Keatah]

This might not belong here, but...
I wrote this free verse poem in awe of the XR2. The title actually means something else: http://tinyurl.com/2dgp7ho
I totally warped the assignment...got an A tho :lol:

Oh yeah, and the XR2 cockpit is hilarious. The only way it could be funnier is, when you press Esc 3 times, confetti blows out of the top hatch. :happybday:

How is the XR2 cockpit funny?? Seems all business to me..:huh:

 

[Coolhand]

i'm not sure, river crab seems to think that i require his approval and care what he thinks or something like that.

But then he's been a pillar of the orbiter community for so long, how could we not take him seriously?

 

[Xyon]

Now -that's- hilarious.

 

[River Crab]

Spoilers follow!

1. Furry Dicez
2. Cup holders and Slurm
3. "Do not press unless you really mean it" button
4. Marvin
5. "Axial velocity (something)"
6. 2001 Space Toilet instructions and life monitor

Probably more...

What does the DGIV have? A "Merry Christmas" message?


I've been here how long, and I already have such great friends.
It's all in part to my incredibly well thought-out word choice.
It's like you put a positive spin on everything I say!

 

[Xyon]

What, are you saying a man shouldn't develop addons with a sense of humour? I for one enjoy those extras.

 

[River Crab]

I mean it for real, when I say that I enjoyed them too. That's what I meant all along! I didn't mean anything about cockpit design. I mean the easter eggs are funny. Not the cockpit or the VC in normal use and aesthetics. We should be thankful it even has a VC. And the Mk II? That's a whole new level.

Also, I'll have everyone know that I'm new to forums. In fact, this is the first forum I've ever actually posted on. The sense of cooperation and helpfulness here is something I've never seen in an internet community. But, I'm still a newb...I never meant to come off in such a way...actually my first post ended up being rather harsh, since I lost what was going to be my first post due to accidentally closing the tab...now I've already managed to make myself look like a total smeghead. Not good for my forum fears...
Anyway, sorry for sounding so forceful.

I still thank Coolhand for the warm reception I got when joining. And I mean, right when I saw the post, when my post count was still 2, I thanked it.
I'll make it clear here and now: Dbeachy and Coolhand are my forum idols. They also are developer idols. Such devotion and time poured in to the Orbiter community even though they don't get paid, nor do they actually have slave labour- you two prove that the internet is not bad. Actually, you two, you are second only to the mighty Probe himself.

I'm not trying to suck up, but I'll make my opinion clearer now.
As for the XR2...if I haven't made it evident, the XR2 is like my new drive in life. I live to fly her. The XR2 is a work of art, just like Falling Water, the Mona Lisa,and the Ode to Joy. It's intricate as the F-35 and whimsical like the starship Enterprise.
It's indeed beautiful, but not only. It's more beautiful than "Cellar Door" beautiful. There isn't a single word to describe it. Not in the English language, and certainly not in the diluted American English of today. Not in Japanese, not in Chinese, German, Russian, French, Spanish, Portugese, Swedish, Hebrew, Ainu, Esperanto...not in any language.

The XR2 is many things...but what it is not, is half-baked.

 

[loading]

At least the Furry Dicez are "official" equipment inside the cockpit of a spacecraft.
(see pic below; left side above the camera)

btw: I just thought "What the ", when i saw that a few days ago on NasaTV.
Is stuff like this normal inside the shuttle?

 

[Coolhand]

ah, those space shuttle cockpits, THEY ARE SO TEH FUNNAY!!!1!!!.:happybday:

 

[dgatsoulis]

There isn't a single word to describe it. Not in the English language, and certainly not in the diluted American English of today. Not in Japanese, not in Chinese, German, Russian, French, Spanish, Portugese, Swedish, Hebrew, Ainu, Esperanto...not in any language.

Actually there IS a single word that can describe Coolhand's (Steve Tyler's) and dbeachy1's (Douglas E. Beachy's) contribution to Orbiter.
-It can certainly describe EVERY single addon-developer's state of mind when they are... ehm... developing an add-on.
-It can describe every answer to every post in this Forum. (Even the "Galkin Empire" one's)
-It can even describe Dr.Schweiger's "need" to come up with this amazing educational tool. (That turned out to be so much more, for so many people around the globe).
It's a word that has been passed down to us from the civilization that developed Physics and Democracy among other things...
That word is Filotimo

The definition written in English in that link above, will not help you understand the true meaning of that word.
You will get really close to it... but not completetely understand it.
For me... it means "to give, selflessly, to as many people as you can around you, and expect nothing in return."
But it's not exactly "Altruism". It's so much more than that! Can't really explain it in English, even the definitions in Greek dictionaries fail when they try to define that word.

I do know this: There is certainly a lot of "Filotimo" in Coolhand's work!:thumbup: