A video posted on YouTube on Wednesday appears to show the world record time for a robot to solve a Rubik's Cube being reduced to fine primary-colored particles. If made official, the time of 0.38 seconds, not much more than the blink of an eye, would resoundingly beat the current holder, Infineon's Sub1 Reloaded, with its time of 0.64 seconds.
The nameless robot is the creation of MIT robotics student Ben Katz and software developer Jared Di Carlo, though Katz describes it as a "contraption." Katz re-used motors from other robotics projects as well as others sourced from eBay, as well as two US$7-PlayStation Eye cameras. These are positioned at opposite corners so all the faces of the cube can be seen.
"We used the cheapest cube we could find on Amazon Prime because we thought we'd end up destroying many of them, but somehow ended up only going through four cubes and hundreds of solves." Di Carlo writes in a blog post. Here's a video of one such failed attempt.
The pair largely attributes the impressive time to using better motors. "We noticed that all of the fast Rubik's Cube solvers were using stepper motors, and thought that we could do better if we used better motors," Di Carlo explains. "So we did." Specifically, the pair used six Kollmorgen ServoDisc U9-series motors. These need only 10 ms to perform a quarter turn of the cube, reaching a rotation of 1,000 rpm in that time.
The robot uses the min2phase algorithm to solve the puzzle, taking the data received by the cameras and converting it into a sequence of moves for the motors to execute. The algorithm, now several years old, was written by software developer Shuang Chen. But much more input was needed on the software front to enable an actual machine to physically solve a puzzle, including work to synchronize the motors to prevent collisions when making moves.
Surprisingly, they found that tightening the cube to make it harder to turn actually helped. "When the cube is loose (like it would be if a person were trying to solve it fast), the outer faces just cam outwards when you try to turn the center faces quickly," Katz explains in a blog post. "It took tightening the cube way past what intuitively felt appropriate, in order to stop the camming action from happening."
Katz thinks that with further tuning the record could be brought down a 100 ms. The time could potentially be reduced further with a solve requiring fewer turns. The algorithm used typically needs 19 to 23 moves to solve a cube. The record time was set during a 21-move solution.
That said, there appears to be some doubt as to whether the pair will try again. "For the time being, Jared and I have both lost interest in playing the tuning game," writes Katz. So if you fancy taking a crack, all you really need is a handful of motors, a few cheap Rubik's Cubes, a couple of webcams, and some serious robotics hardware and software engineering knowhow. Good luck!
You can see the record-breaking video below.
Sources: Di Carlo's blog, Katz' blog