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Distributed Robotics


Molecule

Up Version 1 Version 2 Version 3 Simulation

Version 3

The difficulty with the connectors in version 2 forced a radical design change in version 3.  Electromagnets were not working very well and their power consumption was also of concern.  Because electromagnets must remain energized to maintain a connection, a great deal of power would need to be consumed to keep a structure from falling apart.  This issue was realized from the beginning, but a practical alternative to electromagnets was proving difficult to find (we always assumed we would dump the electromagnetic connectors as soon as we found a better solution, but it wasn't happening).  The key constraints of Molecule connector design are:

  1. Must be quad-symmetric (units need to attach to each other at at 90-degree orientation),
  2. Must be no taller than 23/32",
  3. Should consume power only when a connection is being made or broken,
  4. Should retract inside the atom bounding sphere when not connected, and
  5. Should be unisex.

This is a huge design challenge, especially the space requirement which leaves very little room for moving parts.  Our analysis showed that it would be almost impossible to make an active connector within the 23/32" restriction, let alone one that could retract.  However, we eventually realized that it might be possible to fit one active and one passive connector in 46/32" space.  The only problem was constraint #5.  This constraint was actually a leftover from our early design meetings--we had since realized that Molecules partition 3-D such that there are two distinct "flavors" of Molecules and each flavor can only connect to the other.  Therefore, constraint #5 was not really necessary, but it seemed practical at the time it was conceived.  The result is that we have abandoned unisex Molecules in version 3--Molecules now come in male and female varieties:

The female Molecule with passive connectors.

The male Molecule with active gripper-type connectors.

These movies show how the Molecule moves and connects to other modules:

Molecule Degrees-Of-Freedom
(? MB AVI, DivX codec)

Molecule Gripper Connector
(? MB AVI, DivX codec)

Here is a movie of our first multi-Molecule reconfiguration:

Pair Reconfiguration
(? MB AVI, DivX codec)

Photo of a a four-Molecule structure:

Two Molecule Pairs

In the following movie, the leftmost Molecule pair translates to the right of the 4-Molecule structure. The ability to translate a pair from one side of the structure to the other allows a global translation of the structure by successive pair translations. For a structure of this size it is necessary to provide a stabilizing base to which the male Molecules can attach. This is needed because there are not enough stationary Molecules to provide a stable structure when certain moves are done by a moving male Molecule (the torque needed to move a male can tip the structure made up of the other three non-moving units). The base would not be necessary if we had more units. Note that the speed of this movie has been increased by a factor of three--normally a gripper connection takes about 15 seconds which makes the movie a bit too tedious to watch in real time...

Pair Translation
(15 MB AVI, DivX codec)

Despite what I said above, it is possible to do a pair translation without the base. This requires some non-standard angle rotations and some extra moves to stabilize the structure, but it works pretty well. As usual, this speed of this movie has been increased by a factor of three...

Pair Translation Without the Stabilizing Base
(17MB AVI, DivX codec)

This movie shows a complete locomotion sequence with each Molecule moving once.  Again, it is performed without the stabilizing base.  The speed of this movie has been increased by a factor of 6...


4-Molecule Locomotion Sequence
(19MB AVI, DivX codec)

Four high resolution snapshots of a reconfiguration sequence (1MB each):

Go here for more high-resolution Molecule images.