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Project Description

Problems and Modifications

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Initial Prototype Design

     The goal in constructing a new tentacle actuator was to create a tentacle that was just as functional as the original with the added ability to adjust where bending segments terminated. In this way, the initial prototype was designed very similar to the original tentacle. Both had two bending sections segmented by equally spaced cable supports threaded onto a flexible spine.

     However, the new tentacle's design incorporated two major differences from the original. First, the new tentacle was designed so that all the cable supports other than the one at the tip of the tentacle would not be fixed in position on the spine. It was intended that this would allow them to slide along the spine, making the location of each one adjustable. And since the bending segments end at specific cable supports, this should allow the lengths of bending segments to be altered by manipulating where they terminate.
     Second, tension springs were added to the design of the new tentacle. These springs were threaded onto the spine between each of the cable supports, and the cable supports were then attached to the springs. Because the cable support at the end of the tentacle was fixed in place the springs would naturally pull all of the other supports toward the end of the tentacle. This would be counterbalanced by tension in the cable tendons which were pulling in the opposite direction. It was also thought that because all the springs used were identical, they would exert equivalent force and tend to keep all the cable supports equally spaced within the bending sections.

     The parts used in the prototype's construction were relatively simple.  The cable supports were made from a clear plastic, cut to form.  Surplus cable supports from the original tentacle were located and used.  The original tentacle had seven supports per bending section, but only enough surplus supports were found to allow the prototype to have five per section.  The center hole in the supports was 1/2" in diameter.  To make this diameter better conform to the size of the spine a vinyl spacer was inserted in each support.  Notches cut in the spacers held the ends of the springs.  The spine was also surplus from the original tentacle.  It was made of a highly flexible plastic composite called garulite.

     Minor problems with this design were noticed during the construction of the prototype.  These were corrected at that time through slight modifications.