How would you (or would you) preserve F2L pairs during the cross in this scramble?

[bundat]

Ok, given this scramble (cross on bottom)
F U' L2 F2 R L U2 L R U2 L2 U2 F2 B2 L2 U2 B' L U B' D2 B' R F D

I got this from cubetimer.com.
I noticed that there were already 2 F2L pairs on the B face, and I guess if I were a block-building master I would've had a double xcross? (or not, I don't know)

Anyway, can anyone tell me how they would approach this one?

I usually encounter cases like these and they mess me up because I try too hard to preserve the pairs.
e.g. I normally take 2-2.5 seconds to solve the cross, but here it took me 10 seconds just because I couldn't solve the cross in my head during inspection (while being able to preserve the F2L pairs), which made the 2 pairs a total waste seeing as how an F2L pair takes me 1.5-3 seconds.

 

[Ellis]

If my goal was to really get a double x-cross I would probably do

(D2 F D' R' D2 y' L' D F2 D') L U' L2 U L

I'm not gunna lie though, I really wouldn't do that in a normal solve. I would probably just do the best cross that I saw and hope that one or both of those pairs stayed paired, which I know one of them would not (but there's still one ). Or just track one pair and make sure it doesn't separate. I should probably say that I'm terrible at blockbuilding and I'm sure there's a better way to do this.

 

[TheJoker]

hey this is a nice scramble... slow solving it for the first try... i got 13.21 seconds... and a PLL skip also... if i consider it as my PB ... take note i'm a sub23 consistent and sub20 inconsistent... wow...

nice scramble... i will save this scramble...

Scramble: (white bottom, red front)
F U' L2 F2 R L U2 L R U2 L2 U2 F2 B2 L2 U2 B' L U B' D2 B' R F D

solution:
cross = (y) R' B2 R D2 L D' F' D2 = 8 moves...
1st F2L = R U' R' = 3 moves
2nd F2L = U' R' U R = 3 moves
3rd F2L = (y) R' U' R U' R' U R = 7 moves
4th F2L = U L U' L' = 4 moves
OLL = U R' U' R' F R F' U R = 9 moves
PLL = U2 = 1 move
TOTAL = 35 moves...

that is the best i can do to preserve those 2 pair... and solve the cube... and it was fast...

hope there is the best way cuz i hate B/B'... heheheheh...

 

[JohnnyA]

Cross+preserve: y2 F' R2 F D2 B D' L' D2 (8)
F2L: y L U' L' U' L' U L y' R' U' R U' R' U R U L U' L' (18)
OLL: (y) R' U' R' F R' F' U R (8)
PLL: U' (1)

Total: 35

Whoa. I got the same solution as above, even when speedsolving it? :O

 

[Ton]

I would only do a B2 (this moves them out of the way), than make the cross

That as far as I will do in a competition

Preserve B2
then the cross
L U L F' U2 B2 D' (7)

 

[MistArts]

D2 F D' R' D2 B2 U' B' U2 M U2 M'
U2 R U R' U' R U R'
L' U2 L U2 L' U L (30)
f R U R' U' f'
N-PLL

Not that great but it was the first time through without taking back moves.

 

[person917]

I also fall into this problem sometimes...think it would be ok if you would put the 2 f2l pairs where they're suppose to go then insert the cross edges using different combination of M moves?

 

[EmersonHerrmann]

I would only do a B2 (this moves them out of the way), than make the cross

That as far as I will do in a competition

Preserve B2
then the cross
L U L F' U2 B2 D' (7)

I did the same thing Makes the simplest and best solution if I were speedsolving it.

 

[TheJoker]

yeah... you may not see it in actual competition... so majority here will solve it as it is...

but thread starter want to know how to do it... and i inspect the cube... it took me a little 18seconds to see my cross and 2 f2l were preserve...

well i know it is a no-no... when i see the cross... then i speedsolve it... i was just amaze how the formation after cross was formed... so i continue solving it...

if the thread starter didn't tell that there are already 2 f2l fair... i would not see it anyway...

 

[bundat]

I actually came up with the same solution as Ellis, which felt awkward to me for a speedsolve.

The way Joker and Johnny solved it makes the scramble look crazy (automatic F2L pairing plus PLL skip), but the cross itself seemed awkward (to me) to plan out during inspection (the F2L pairs had to be moved around several times I think, just to avoid being destroyed).

MistArts' solution... I also had the idea of inserting the F2L pairs first and M slicing the cross edge in afterwards, but I thought I wouldn't save much time doing that...was it worth it?

I liked B2 the best, seems like it's the most realistic solution that I am capable of coming up with during inspection (looks very simple and elegant to me)... I just don't know how I'll apply it to other F2L situations though, I guess I should write down and collect other scrambles like that so I can get some practice preserving pairs during the cross...(or should I just not bother..?)

Anyway, thanks for the input guys, much appreciated.

 

[cmhardw]

I got 13.17 on this solve by not trying to preserve the pairs at all. Normally I would try to Xcross (or even double Xcross) a solve if there are pairs already made. In this case though I didn't see anything nice (during the 15 second inspection) that made me want to do Xcross even since the cross was so easy. I've found that if doing the Xcross is much harder than the cross, often it's not even worth it to try.

Now, having said that I took a look at the scramble again after (without reading anyone else's solutions above first) and came up with this.

cross while preserving both pairs: B' L2 D2 F D' R' D2
1st pair: L U2 L'
2nd pair: R' F U' F' R

It's not really Xcross or double X, just a cross that preserves both pairs, followed by inserting those pairs.

The solution I did during my actual speedsolve (with less than 15 seconds inspection) was:

cross: L U L F' D2 F2 D
1st pair: y' (R U R' U')*2 R U R'
2nd pair: d' R' U R2 U R'
3rd pair: y R U R'
4th pair: d2 L' U' L U L' U' L
COLL: y' R U2 R2 U' R2 U' R2 U2 R
PLL: U' L' U L' U' L' U' L' U L U L2

and if I absolutely had to block build, I would probably do a partial double Xcross like this:

Partial double Xcross: y D2 L D' F' D2 R2 U' R'
3rd pair: U2 y' R U R' U' R U R'
4th pair: U' r' U' l' U l U r
complete the F2L: U' M U2 M'
COLL: F R U' R' U R U2 R' U' R U R' U' F'
PLL: U2 R U' R U R U R U' R' U' R2

This solve finishes the F2L in 28 moves, which doesn't seem like much of a saving considering the chance to have had an F2L edge in the 4th cross piece of the partial cross, as well as the chance that the other cross edge would flip in the U layer (which is not bad, but slower to insert after a partial cross than if you can use M moves). So in short, I would not have done this solve in real life, this is just if I had to block build, that is what I would do.

Chris

 

[bundat]

Wow, thanks Chris.
That post gave me a lot of insight.
I guess what I was trying to do was similar to trying too hard for an xcross everytime.

I found it interesting in your actual solve that you didn't even try to preserve not even ONE pair, but instead went for the easy cross, and probably just look-ahead on your first pair.

As for the block-building solution, wouldn't you be able to get rid of those potential problems if, after forming the partial-double-xcross, you insert the missing cross edge using M, before starting on the other F2L pairs? I managed to complete the F2L in 26 moves by starting with your partial-double-xcross, inserting the missing cross edge, then doing F2L.

Anyway, thanks a lot for the input.
On an unrelated side note, your solves made me REALLY want to learn COLL.
Especially considering that my edge PLLs are my fastest ones.

 

[DavidWoner]

2xcross: x2 y U2 R U' F' U2 y2 z' U R U' R2 U2 R2 U (12)

x2 U' R' U x' U' R' U (18)

x l U R U' (22)

z' U2 F R U R' U' R U R' U' F' (33)

U R U R' y' R2 u' R U' R' U R' u R2 (46)