Best way to randomize a cube

[Cynthia Moore]

What's the best way to scramble a (3x3) cube so I can practice?

I've been reading up on cube algorithms so I can help my grandkids. I'm getting pretty good at the first two steps. I got to wondering if I am scrambling the cube sufficiently before each practice. I just "randomly" twist faces and the cube. But I know humans are not really capable of being truly random. We tend to do things in patterns. I typically do something like 10-15 twists and rotations. Is that enough? Will more iterations make it more difficult? Is there a better way?

Thanks

 

[TDM]

Use a random state scrambler, such as qqTimer. That randomly generates a cube state and tells you how to reach it, so every state has an equal probability.

 

[tseitsei]

10-15 turns is not enough. There are positions that take 20 turns to reach optimally.

Best way to get a truly random scramble is using random state scrambler. For example http://www.qqtimer.net/

EDIT:Ninja'd

 

[Bindedsa]

If you go to this website you should see a string of letters, If you don't know what that means watch this video or you can go to this site for a written explanation and you will be able to preform these moves on the cube, leaving your cube sufficiently scrambled.

If you just want to be able to solve the cube for fun and are not worried about the cubing being truly random, I would recommend 25-30 turns. While some states are arguably more difficult, unless you are reversing the scramble the difficulty is not directly related to the number of turns. You want to go beyond 20 moves because until you reach that points some state are not possible to occur.

 

[Stefan]

Already 9 moves produce over 3 billion combinations, so that's gotta be enough!!!

Seriously, though, about 99.8% of all positions aren't reachable in 15 moves. See bottom right stats on http://cube20.org/

 

[sneaklyfox]

If you don't want to be at a computer to use a computer generated scramble, the most random you could get is to throw the cube up in the air and do a turn after each catch. And maybe do this about 15 times? But if this takes too long, what you're doing is probably fine. Even though you won't reach nearly all possible positions on the cube, you're still practicing the same methods. And I don't think anyone here can even solve 0.000... (many zeroes)... 01% of all possible positions in their lifetime.

 

[brian724080]

the most random you could get is to throw the cube up in the air and do a turn after each catch.

That would actually be a really cool way to scramble a cube. Imagine doing that in public, and if someone asks you what you're doing, you just answer casually, "just scrambling my cube".

 

[Cynthia Moore]

I'm not trying for mathematical rigor, just practice. It sounds like 8-10 twists should be enough to give me a decent state for practice. To ensure a more complete test case, something like 20-30 twists would be better.

Thanks for the suggestions. I had no idea how much math had been devoted to this puzzle.

 

[10461394944000]

about 15 times

no you should do at least 20-25 or something

I'm not trying for mathematical rigor, just practice. It sounds like 8-10 twists should be enough to give me a decent state for practice. To ensure a more complete test case, something like 20-30 twists would be better.

no that is wrong

you should always use a random state scrambler like people told you to, or at least 20 moves if you are handscrambling

I have a 3 second average of 5 with 8 move scrambles

 

[qqwref]

8-10 or even 15 turns is NOT okay. If you don't do at least 20 random turns, it is literally impossible to even reach some positions. And with a low number like 8-10 turns, you will have much easier scrambles. Then you will get times that are way lower than you should be getting. That is cheating.

In competition (or on good cube timers), we use random-state scrambling. That means: pick a random position, and give you a sequence that gets there. That way you can just do the moves (usually about 20) and you will get a quality random scramble.

 

[GlowingSausage]

25 moves

 

[Stefan]

It sounds like 8-10 twists should be enough to give me a decent state for practice.

What gave you that impression?

 

[uberCuber]

What gave you that impression?

It gives her a few billion different positions to use!!

 

[10461394944000]

It gives her a few billion different positions to use!!

I rarely do 3x3 sessions of more than 50 solves, so maybe I should start using 2 move scrambles because there are over 200 possible positions !!

 

[Cynthia Moore]

C'mon, guys, lighten up. I'm not trying to set any speed records or test every possible combination. I just want to get good enough that I can show a young child how to do it.

 

[Lucas Garron]

C'mon, guys, lighten up. I'm not trying to set any speed records or test every possible combination. I just want to get good enough that I can show a young child how to do it.

Considering that it's so easy to use a perfectly random scramble these days (the same couldn't be said 5-6 years ago), you should definitely try to.
It might already save you time now, and will definitely be a good habit if you continue this into the future.

I usually go to qqtimer.net if I need some quick, high-quality scrambles.

 

[Stefan]

I'd still like to know what gave you that impression...
Really hope it wasn't my joke.

 

[Jokern]

If you scramble the cube using 15 moves, this will be sufficient to get any case (Any cross case, any F2l case, any LL case) but it will give you easier solves because some easy cases will be more common than others.

If you scramble the cube with random moves you need between 30 and 40 moves before every state is about equally likely. (Source: some post on this forum which I can't find now which did a statistical analysis of random scrambles)

 

[PJKCuber]

I need a scrambler for 2x2 that will give me 50 scrambles at a time and not separately .

 

[Renslay]

I need a scrambler for 2x2 that will give me 50 scrambles at a time and not separately .

How about the official scrambler?
https://www.worldcubeassociation.org/regulations/scrambles/
(If I understood correctly, you need a list of 50 scrambles at once. You can do that with that scrambler.)