Robotic Figures: Revector Blocks
Revector blocks, the red objects in the robot pictured at right, are the most novel and complex components of this series of robots. They are an essential technology for compact cable-driven robots.
Revector Blocks are devices that change the direction of several cables in specific ways. A revector block is an epoxy casting with several curved Teflon tubes embedded in it. These tubes act as pathways for the cables that carry mechanical power though the robot.
Different runs in the robot require different cable grouping geometries. For example, closest to the motors, the cables are arranged as a cone. Through the torso they run in parallel as a tight hexagonal group. A revector block is what transitions the cables from cone to parallel-hex. This is the "hip revector plug", the lowest red object visible at right. It contains 37 tubes, each with a specific starting and ending position and direction in space; or more concisely: entry and exit vectors.
Here are pictured some of the tools and steps for the creation of a hip revector plug. Foreground left is a completed unit that awaits trimming and installation. Left rear is the main mold / jig which has a RTV rubber inner mold and metal support and guide structure. Center is a "37 tube hex starter group". This was held in position by the tan "37 tube grouping tool" next to it. The grouping tool is held in the top of the big aluminum cylinder for the epoxy pour that creates the starter group. The starter group will be trimmed and go into the main mold for routing.
By far the most complex part in the robot is the sternum revector block, shown here in action. It takes in 37 cables in parallel from the bottom and breaks them into 2 arm groups of 12 cables each, a 7 group straight up to the head, and 3 angled pairs which operate the #1 shoulder joints and the #1 head joint.
Constructing the above mentioned sternum revector block requires some strange equipment and many steps, each of which must be done correctly. Shown here is one of the last steps. The tubes have all been routed according to the blueprint and fixed in place. The RTV rubber mold is ready to be closed. After that, the final epoxy pour will be done from the hole in the top. After curing, the stubs will be cut off and the block cleaned up and installed.
Another type of revector block is for the neck joint. A finished part and the mold that created it are pictured. In this hemispherical socket a Teflon ball will sit, and upon this ball the head will be attached. 4 cables eminate from the rim of the socket to give the head left-right as well as front-back motion. Head azimuth motion is provided by the turntable that the revector block rests on.
The smallest, simplest revector blocks are the shoulder units. A distal shoulder revector block and its mold are shown. These units take a tight pack parallel group and fan it into a single row destined for a bender. The proximal units also output a pair of cables for the middle shoulder joint driven disks.