Construction

Each muscle tendon wraps around one of the joints, in its own groove, thus passing from the side with the servo to opposite side where it is fixed to the appropriate arm segment. The biarticular muscles pass around grooves in both the shoulder and elbow joints, thus generating torques on both segments when contraction occurs.

The arm is controlled via a microcontroller network composed of two Brainstem modules and one Moto module. The modules communicate thru an IIC interface. Much of the specific communication protocol is encapsulated by the Brainstem API, common to both the Brainstem and Moto modules.

The optical encoder is attached to the outer pulley. The inner shaft rotates the internal encoder disk.

The muscles are actuated using a simple hobby servo. The servo is controlled directly with a pulse-width-modulated signal from the controller.

The artificial muscle tendons are shown in the figure. The tendons have different elasticities. These are color coded for easier identification. A medium tensile fishing line is used to attach the tendons to the joint connections.