Redesign of Tetrahedral Robot Nodes
Lief Nelson
Exploded view of node components
Completed node
Summary
Hope College has been doing research for NASA on the TET Project since 2006. The first robot
they constructed was the simplest 1-TET, followed by the 4-TET, and in the summer 2008 they made the
4-TET wireless. Previous robots just used flower pots with the bottoms cut out for the robots nodes,
once it became wireless it was necessary to fabricate nodes that could support the robot and contain
the power supply and other hardware. The current nodes, while full filling these requirements, generally
inhibit some of the TET’s motion and do not always behave predictably, such as not always laying flat on
the ground or oriented for the next motion. It became apparent that the node should always land on
one face but still be able to hold the hardware.
All the concepts created were in some way a hanging node, that way the node always landed on
the bottom because for all the nodes the center of mass was low. All concepts featured a bearing with
the entire node below the point of connection for the struts, this would allow for the least interference
for the TET as it moves.
The final design had two parts the cage and the strut connector. The cage was a pyramid shape
and used a piece of sheet metal as a platform for the hardware; it also will provide support for the
robot’s weight. It also featured a cup shape at the apex to press fit the plane spherical bearing. This
bearing was used to give the strut connector some tilt when the node is resting flat on the ground; also
it helps the node in the air to reorient toward the ground as the TET tumbles. The second major part of
the node is the strut connector; this was an assembly of modified u-bolts and a fabricated plate with a
peg on the bottom. The plate had holes drilled on its four sides and on the top so each face had a u-bolt
threaded through an eyelet. The eyelets were the part to screw into the existing struts. The peg of the
strut connector was pressed into the inner diameter of the bearing. Once the prototype was assembled
it was connected to a tripod and run through a simulation of a 4-TET tumbling. The bearing did its job
and the node was able to land flat and in the correct orientation every time.