Our first design idea is inspired by real vertebral columns. It includes many 3D-printed plastic vertebrae connected by rubber intervertebral discs. This design should allow the tail to bend in any direction, like a real tail. Three control cables run through each vertebra near the outer rim and attach to the vertebra at the end of the tail. The tail can be moved by pulling on the cables.
With two sets of cables, two sections of the tail can be controlled separately. The first set of cables attach to the vertebra halfway along the tail, and control the near half. The second set of cables extends all the way to the end, to control the far half of the tail.
Unresolved questions
What kind of actuators should pull on the cables to move the tail?
Large amounts of torque may be needed at the base of the tail to hold it in some positions. How do we attach the tail to the wearer firmly but comfortably?
Will the friction between the control cables and vertebrae be enough to cause problems? If it does, bushings or a surface coating of ultra-high-molecular-weight polyethlene might help.
How do we prevent damage when people sit on / trip over / step on the tail? A solution might involve using force sensors on the control cables to move in response to external forces.
Soft concept
The current prototype (2021-11-07) uses a section of tubular foam pipe insulation for the tail structure. Two cables along the upper left and upper right areas move the tail. This video shows a test of the tail movement.
