The EM-J4 is equipped with four of the J4-M3500 although for most activities it will only deploy one or two arms. The arms are retractable, for stowing the arm folds upon itself at the elbow and then draws in. For efficiency during some repairs, the EM-J4 may configure arms for specific tasks, so that it can quickly proceed without having to change fittings by simply rotate until the desired arm is available.
The hand assembly can be detached and a variety of tool heads attached in its place. The arm has a 'shoulder' joint at the top of the drone, capable of rotating 360° provided the the arm is lifted. The shoulder has an up/down range of 135°. There is a joint midway in the arm, it can rotate freely on its main axis. The lower arm joint is capable of moving 180°. The hand contains six fingers for gripping onto items. The wrist of the arm can rotate 360°