How the robotic arm moves

The rover arm has an overall reach of 90 centimeters (3 feet).

It has three joints (like the human arm, a shoulder, elbow, and wrist) with five geared motors to enable the following movement capabilities:

Shoulder

Two motors are in the shoulder for side-to-side (horizontal) and up and down (vertical) movements. The shoulder can move in the horizontal plane 160º. If the arm moved farther from left to right, it would hit the front rocker-bogie "leg" portion of the wheel suspension. The shoulder can also move the arm through 70º in the vertical plane.

Elbow

The elbow joint, midway down the arm, is powered by another motor and can move through 290º, folding the arm up or out.

Wrist

Two motors reside in the wrist to twist the "handful" of instruments vertically and horizontally to place the chosen instrument perpendicular to the target surface. The wrist can rotate vertically through 340º, more motion than the human wrist. Functioning similar to a Lazy Susan, the turret handles the horizontal wrist rotation, and can spin through 350º.

The arm works in conjunction with the Hazcams, which take pictures of the intended rock targets. The computer software uses these pictures to position crosshairs on the surface of the target. The arm can then adjust its approach angle to safely line up and deploy one of its four science instruments.

At the end of each instrument are contact sensors, sophisticated "curb-feelers" that tell the arm motors to shut off when the instrument has made contact with the surface of the target.