| | A telecube G2 module fully contracted. |
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Telecube modules are cube shaped modules with faces that can extend out doubling the length of any dimension. Each face "telescopes" out, thus the name. Each face also has a latching mechanism to attach or detach from any other face of a neighboring module. We have experimented with shape memory alloy and permanent switching magnet technologies in various versions of this system.
This work builds on the "Crystalline" robot by Marty Vona and Daniela Rus starting at Dartmouth. Their initial Crystalline modules are 2D squares with one degree of freedom (all faces expanded at the same time). The telecube modules are 3D with every face having the ability to extend or contract independently.
One module reconfigures from one site on a virtual grid by detaching from all modules except one. Then extending (or contracting) the faces that are attached
the module moves to the neighboring site.
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In 2D with 8 modules an example reconfiguration is similar to the 9 piece sliding tile puzzle. The module in the upper left corner moves to the center.
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Telecube Design
Click on the image to toggle between collapsed and expanded.
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The target size for the module is a cube that is 5 centimeters on a side. Packing actuators, electronics and structure into that small size to get the needed functionality is one of the more difficult parts of developing the module.
There are two main mechanical functions: 1) latch/unlatch from neighboring faces and 2) Telescope the faces (expand/collapse). Each of the faces, called a connection plate, has a remotely controllable means to reversibly clamp onto and to transmit power and data to the neighboring module. The devices which produce the linear extension/contraction and module to module clamps are called the telescoping-tube linear actuator and the switching permanent manget devices, respectively.
Telescoping-tube Linear Actuator
The linear actuator primarily a motor and leadscrew with an inlined housing. The off the shelf maxon motor and gear box has a diameter of ~13 mm and thrust capacity of ~12 N. The telescope has two stages (three tubes)and stroke length of 36-40 mm. Another difficulty with these systems is that the modules tend to sag when cantilevered under gravity. This means that the telescoping part of the actuator must be highly precise and light weight. So, proper materials must be chosen to have enough stiffness, be light weight, low friction and have enough precision without being prohibitively expensive.
Switching Permanent Magnet Latch
The cover of the switching permanent magnet is shown transparent so the magnet array is seen as colored disks; blue for "north" and red for "south". Click on the image to toggle on and off.
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The flux lines of permanent magnets are routed so that the device either extends the magnetic flux (e.g. grabs onto ferrous metals) or hides the magnetic flux internally (e.g. no magnetic attraction). This is the same type of device used in some machining clamps and fixtures, except extrememly small. (We have constructed perhaps the world's smallest switching permanent magnet.) Each face has two switching permanent magnets devices, one on each corner and two high magnetic saturation plates for the opposing magnets to grab onto on opposite corners. There is an array of 16 NdFeB disc magnets in each device. When half of the magnets are slid by one row, the flux lines are completely captured.
An estimate of the the flux density of each NdFeB disc is ~0.35 T which means the its holding force on a magnetic metal is ~160 g. Therefore, for each permanent magnet device the estimated holding force is 25 N. Since torque to due cantilevered loads are more likely to limit the number of modules that can be held, the magnet devices are positioned at the corners of the plate. With a moment arm length equal to that of the distance between the longitudinal axes of the plate and the magnet device (15 mm), it is estimated that two modules could resist a torque of 0.75 Nm which is more than sufficient.
Demonstrations |
Videos of the functionality of several first generation prototypes along with
simulations of shape forming, manipulation and locomotion. |
Publications |
We have published variety of conference papers on the mechanical design,
local behavior based control, and shape reconfiguration planning. |
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