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# Rubik's Robot

Posts: 18,647
edited June 2012 in Robotics
Personally, I never gave a flyin' fandango about the Rubik's Cube craze (which is on the rise again) but this Lego-based unit is fascinating to me. Yes, it's very slow compared to some amazingly fast ones out there, but IMHO this one is within reach for the home hobbyist to build, for a normal 3x3x3 cube. Hobby servos can do all the work here. The heck with the smartphone camera app, a simple colorpal could be used to read the block colors. Under the control of a mighty BS2! Two BoeBots with rotating grippers working in unison would be sa-wheat.

I'll get a round tuit eventually if no one beats me to it.

@Ken: Get me a ColorPal, Pal !
"When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

- Pablo Picasso

• Posts: 10,002
edited June 2012
The color pal would have to be held up to each square to determine the color. I think this is a job for Phil's NTSC video capture.

If could read the colors of the squares a side at a time.

In the earlier '80s I used to play with the Rubic's Cube. I wasn't ever super fast, but I could consistently "solve" the cube in under two minutes. I put "solve" in quotes since I really just memorized a series of moves based on which piece I was positioning.

This would be a doable project, but who has the time?

If anyone finds a copy of the "Ideal Solution" to the Rubic's Cube (preferably electronic version), I might give this a try sometime. I don't remember how to solve the cube anymore and the Ideal Solution was the the book I used to learn to solve it. I think it would be easier for me to understand the solution in that book since it would be familiar to me.

I'd hardly have to build any hardware at all. I could use my robot arm to position and rotate the cube. I'd just need to build a secure square hole next to the arm to hold the lower two thirds of the cube still while the arm rotates the top layer of cube.

The trick would come in programming the arm.

On second thought, I'm not sure my robot arm could manipulate a RC as it is. I remember trying to get it to pick up an empty soda can; it had a very difficult time picking up the can. I might need to make some modification to the arm in order for it to manipulate a cube.
• Posts: 18,647
edited June 2012
Duane Degn wrote: »
The color pal would have to be held up to each square to determine the color. I think this is a job for Phil's NTSC video capture.

If could read the colors of the squares a side at a time.

That would speed things up, for sure. But you know me. I'm a simple guy. Most bang for the buck. I'd already have several servos to manipulate the cube, certainly one would be for vertical lift to spin the different levels. If I mount the Colorpal on a servo for horizontal travel, there's my XY scanner. Simple stuff!

Yeah, I agree, "who's got the time". But as you know, my brother: it's left up to guys like you and me.
"When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

- Pablo Picasso
• Posts: 18,647
New world record just this month, a mere 0.637 seconds to solve Rubik's cube. :)

http://www.guinnessworldrecords.com/news/2017/3/video-robot-breaks-world-record-solving-rubiks-cube-in-0-637-seconds-464392
"When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

- Pablo Picasso
• Posts: 21,492
Okay, that's cool, but I counted only 16 moves in the slo-mo part. What's considered the most "mixed up" starting position, i.e. the one that requires the most moves to solve?

-Phil
Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. -Antoine de Saint-Exupery
• Posts: 10,760
Okay, that's cool, but I counted only 16 moves in the slo-mo part. What's considered the most "mixed up" starting position, i.e. the one that requires the most moves to solve?

-Phil

Any position of the 3x3x3 Rubik's cube, no matter how scrambled, has an optimal solution of 20 moves or fewer. 20 moves is simply the upper bound. In fact, for the majority of possible start positions, the ideal number of moves required — nicknamed "God's Number" — is significantly lower.

tho there is a trade off between compute time and total solution time.
Human cubers do not try for those 20 moves, instead they have 'fast sets' that are optimised for finishing soonest.

The link mentioned 21 moves, so maybe there is 1 possible move added, that allows the solve time to be slashed for a lower total time.
• Posts: 73
edited March 2017
Duane Degn wrote: »
The color pal would have to be held up to each square to determine the color. I think this is a job for Phil's NTSC video capture.

If could read the colors of the squares a side at a time

That's the way the Lego Mindstorms based tilted twister does it.

You can build one of these just using one standard Lego Mindstorms kit.
• Posts: 18,647
Tilted Twister is on wheels. Calll me when it does a figure 8 while solving the cube!
"When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."

- Pablo Picasso
• Posts: 73
Okay, that's cool, but I counted only 16 moves in the slo-mo part. What's considered the most "mixed up" starting position, i.e. the one that requires the most moves to solve?

-Phil

In 2010 Tomas Rokicki, Herbert Kociemba, Morley Davidson, and John Dethridge proved that "God's Number" for the Cube is exactly 20.

They used about 35 years of CPU time to (effectively) solve all 43,252,003,274,489,856,000 possible cube starting positions and found that no position required more than 20 turns to solve.

cube20.org/