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## Lego Robot Solves Rubik's Cube Puzzle In 3.253 Seconds60

SternisheFan sends this news from CTV: "The Cubestormer 3 took 18 months to build but only needed 3.253 seconds to solve [a Rubik's cube], breaking the existing record. Unveiled at the Big Bang Fair in Birmingham, U.K., the Cubestormer 3 is constructed from the modular children's building-block toy but uses a Samsung Galaxy S4 smartphone with a special ARM chip addition as its brain. It analyzes the muddled-up Rubik's Cube and powers each of the robot's four 'hands,' which spin the cube until all sides are in order. Created by ARM engineer David Gilday and Securi-Plex security systems engineer Mike Dobson, Cubestormer 3's new record shaves just over two seconds off the existing record, set by Cubestormer 2, which the pair also built."

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## Lego Robot Solves Rubik's Cube Puzzle In 3.253 Seconds

• #### alas ! (Score:3, Funny)

on Wednesday March 19, 2014 @03:34AM (#46522499)
Only if I had four hands ..
• #### Re:alas ! (Score:4, Interesting)

on Wednesday March 19, 2014 @04:02AM (#46522565) Homepage

Well, I guess it also depends on "how well" the cube is when you start.

Is there anybody that knows the longest possible sequence of move one would have to do in order to resolve the cube? In order words: what is the worse configuration to start with when you try to resolve it.

I think our robot could spend more than ~3 seconds resolving it with worse configurations.

Now: Let's design a robot to mix the cube for the other robot and have a data set, not just one run.

• #### Re:alas ! (Score:5, Informative)

on Wednesday March 19, 2014 @04:13AM (#46522583)
• #### They can probably compute a just-over-20-move solu (Score:5, Informative)

on Wednesday March 19, 2014 @05:43AM (#46522767) Homepage Journal

As The boojum said, you can theoretically solve a cube in any configuration in 20 moves, but it might take a long time to find that optimal solution. Computers can quickly find a just-over-20-move not-quite-optimal solution, though.

Human-friendly algorithms generally take over 50 moves, with the absolute best solves still taking more than 40.

I stepped through this video frame by frame. They rotate the cube 5 times to inspect each face first (I guess they only have one camera), paused about 0.2 seconds (presumably to calculate a solution) and then they made 21 moves plus 4 rotations to solve it. (The rotations were necessary because it only has 4 arms and can't spin the top and bottom layers.)

So yeah, looks like they computed a nearly-optimal solution, and I imagine they can probably get a just-over-20-move solution every time.

• #### Re: (Score:3)

Is it really necessary to scan every face? I'm no expert when it comes to Rubix cubes (I've only ever managed two sides on mine), but isn't a cube similar to a dice where you can look at one side and infer what state the opposite face is in? When the previous machine was heralded here on /. I recall that the Mindstorms robot only looked at 3(?) of the faces. That seems like a while ago so there's a good chance I'm mistaken about that.
• #### Re: (Score:3)

Nope, you can have 1 face look a specific way but the "back" face look any number of ways. Heck you can solve for multiple sides and have the rest of a sides still be a mess.

• #### Re: (Score:1)

by Anonymous Coward

Yes and no - if you solve 5 faces, the 6th must be solved, but if you solve the top two layers and have some edge pieces on the sides showing the bottom color, you don't know which is which. With corners you can infer the color of the third side by knowing any two colors even thought there are two corners with the same pair because in one corner the two colors proceed clockwise and in the other CCW.

• #### Re: (Score:3)

I stepped through this video frame by frame. They rotate the cube 5 times to inspect each face first (I guess they only have one camera), paused about 0.2 seconds (presumably to calculate a solution) and then they made 21 moves plus 4 rotations to solve it. (The rotations were necessary because it only has 4 arms and can't spin the top and bottom layers.)

Yes, they only have one camera - it's on the smartphone they're using. When you start the machine, the smartphone platform rises, exposing the camera at wh

• #### Re: (Score:2)

camera is the sgs4 itself.

• #### Re: (Score:2)

Back in the late 70s/early 80s I figured out a series of rotations that would rotate only 4 center-edge cubes that was very useful in solving the puzzle, but it was incredibly unwieldly, requiring dozens of rotations. I could usually do the whole thing in about 15 minutes. That was good enough for me...

• #### Re: (Score:3)

As others have pointed out, the optimal solution is never more than 20 moves, and this instance required a bit more than 20 moves, so it probably wasn't the very easiest of configurations. That said, I don't understand why this record isn't for "best average of 20 runs" (or some other suitable number). It wouldn't take more than five minutes to run it, and it would be a lot more telling about the actual capacity of the robot.

It would also be interesting to see the variance of the solving times. How consi
• #### Re: (Score:1)

It was using an underpowered Samsung phone. If they had harnessed the unbridled power of the iPhone 5S's 64-bit technology, it would easily have shaved off a whole second.

• #### Mathematicians, pls (Score:2)

I am afraid other posters have given you the wrong answer.
The longest possible sequence of moves is infinite when the initial state involves swapping two colored stickers.
Source: personal experience.

• #### Re: (Score:1)

Then you would need a girlfriend with four breasts.

• #### Re:SloMo required! (Score:5, Funny)

on Wednesday March 19, 2014 @04:01AM (#46522563) Homepage

That was the slow motion video!

• #### Re: (Score:1)

by Anonymous Coward

'Twas an awful video, if you ask me.

A quick search pulls up a few more. I liked this one, which shows much more usage context, even if no slowmo.

• #### Impressed yet disappointed with Lego (Score:2)

I'm impressed that Lego can do such heavy tasks nowadays. I am sure that my old technic Lego blocks would simply have snapped in two under such stresses. However, I think that the new Lego is so customized that there may exist thousands of different blocks, which means you must now design first, and then order the blocks. It's no longer a matter of having a box full of blocks and just start building. It seems also many blocks are specialized and can only be used in one (maybe two) different way(s), whereas

• #### Re: (Score:2)

There's also the possibility that they just glued the blocks together.

• #### Re: (Score:2)

What glue works well with Legos?

A couple of years ago the local Walgreens had a large knock-off set for \$20. I picked it up as a last-minute Christmas gift for my son but we were both kind of frustrated with it as the pieces wouldn't stick together.

I tried using a super glue gel we had around the house, but it didn't work very well. What glue works well?

• #### Re: (Score:1)

Acetone is the most simple method. Nail polish remover is 70%, but 100% is available at hardware stores.
Brush it on both pieces and put them together. In 5 minutes they are permanently bonded as one piece of plastic.
The Lego Group uses other less user friendly solvents to do the same thing. MEK and GBL

• #### Re:Impressed yet disappointed with Lego (Score:4, Informative)

on Wednesday March 19, 2014 @08:39AM (#46523307) Journal
The first thing you need to know when bonding anything is the material you are bonding, most Lego bricks are made of ABS plastic and I would assume the ones you had are as well. The way you bond ABS is by chemically welding it, you can find the solvent glue at most hardware stores (plumbing section). The glue will be black because there will be abs filler in there to fill voids because it is used in plumbing and must be water tight. The second option is to use MEK (methyl ethyl ketone) to chemically weld it, MEK is clear and has no filler. Most hardware stores don't sell MEK anymore but a MEK alternative that may not work. MEK is some nasty stuff wear gloves when you use it and work in a well ventilated area with a respirator, if you get any on your gloves change them as the MEK will be eating through them shortly.
• #### Re: (Score:2)

There's loads of clear glues for ABS, a quick google search turned up Weld-On #16. Today we have the internets and you can order things from very far away instead of having to settle for what your local hardware store can get.

I personally would pay my local store a small premium to order stuff for me because I live in the sticks and receiving some packages is difficult, but I'm not surprised they don't want to get into that.

• #### Re: (Score:2)

A good alternative to chemical bonding of plastics is ultrasonic welding [wikipedia.org].
• #### Re: (Score:2)

Thanks for that, I had no idea such a thing existed.

• #### Re: (Score:1)

by Anonymous Coward

What glue works well with Legos?

I hear that Kragle works awesomely.

• #### Finally (Score:1)

Now THAT is news for nerds!

• #### Hold the phone (Score:1)

by Anonymous Coward

Generally, contestants for Guinness records are not allowed to measure their own attempt. It appears the timing of the solution was performed by the contestants' gear, which means this is not a legitimate record.

• #### Re: (Score:2)

What makes you think it wasn't also timed by another device?
• #### Applications (Score:1)

Very impressive! I don’t know much about algorithms and stuff like that but what are the real applications for such an achievement?
• #### Re: (Score:3)

what are the real applications for such an achievement?

Impressing chicks. When it comes to meeting girls, lego robotics is right up there with model railroading.

• #### Re: (Score:2)

Try LEGO model railroading. Yes, it is a real hobby.

• #### Re: (Score:1)

Off course...Chicks are really impressed by "fast" geeks.
• #### Hah (Score:4, Interesting)

on Wednesday March 19, 2014 @09:46AM (#46523723)

Try reconfiguring (ie take the stickers off and put them back in diferent places so there is no solution) and then see how the robot does...

• #### Re: (Score:2)

"Different places"? For example, in another part of the room?

• #### Re: (Score:2)

Taking off stickers? Just flip one corner or edge piece and you will have an unsolvable cube.
• #### Re: (Score:2)

Since most solution algorithms are a database attack, I imagine it will kick out as a non-valid position (i.e. not in the database).

• #### They can probably shave another half second. (Score:2)

If they can speed up the optical scan, say get a phone with a faster camera or optimize their scan algorithm, I'm willing to bet they can shave another half second off that time.

• #### Pfffft (Score:1)

If you really want to impress me, build a Lego robot that builds cube-solving Lego robots.

• #### I don't get it (Score:2)

From a mathematical perspective, "solving" the cube means generating the command sequence. Physicallly manipulating the cube is unrelated. So what's the big deal here. Is it:

a) an algorithm which comes up with a solution of 22 moves every time?
b) an algorithm which does (a) in much less elapsed time than previous algorithms (or CPUs)?
c) Some cool shiny robotic manipulators which can twist a (well greased, well-aligned) Rubik's cube faster than previous manipulators?

• #### Re: (Score:1)

d) All of the above.

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