  Benchmarks for robot manipulation are crucial to measuring progress in the
field, yet there are few benchmarks that demonstrate critical manipulation
skills, possess standardized metrics, and can be attempted by a wide array of
robot platforms. To address a lack of such benchmarks, we propose Rubik's cube
manipulation as a benchmark to measure simultaneous performance of precise
manipulation and sequential manipulation. The sub-structure of the Rubik's cube
demands precise positioning of the robot's end effectors, while its highly
reconfigurable nature enables tasks that require the robot to manage pose
uncertainty throughout long sequences of actions. We present a protocol for
quantitatively measuring both the accuracy and speed of Rubik's cube
manipulation. This protocol can be attempted by any general-purpose
manipulator, and only requires a standard 3x3 Rubik's cube and a flat surface
upon which the Rubik's cube initially rests (e.g. a table). We demonstrate this
protocol for two distinct baseline approaches on a PR2 robot. The first
baseline provides a fundamental approach for pose-based Rubik's cube
manipulation. The second baseline demonstrates the benchmark's ability to
quantify improved performance by the system, particularly that resulting from
the integration of pre-touch sensing. To demonstrate the benchmark's
applicability to other robot platforms and algorithmic approaches, we present
the functional blocks required to enable the HERB robot to manipulate the
Rubik's cube via push-grasping.
