| Two segments one expanded one angled. Each segment has two degrees of freedom and a connection plate on top and bottom.
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| The three segment slinky locomotion uses the smallest number of modules and is not completely statically stable as the module
tumbles over with inertia at one point in the gait.
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| The earthworm gait is an extensible gait
(that may be arbitrarily long) and uses a peristaltic type of motion very similar to the one earthworms use.
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| Eleven modules are shown here using a Turning caterpillar gait.
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Segment and Node
Polypod is made up of two types of modules called Segments and Nodes.
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Segments are two
degree of freedom parallel mechanisms composed of 10 links.
The kinematics of the resulting mechanism is similar to two prismatic
joints joined together by a revolute joint where the prismatic joints
are constrained to have the same length. |
Each segment module contains all the components to be a stand-alone robot in
itself (except for power):
| • | Computation: Motorola XC68HC11E2 (generously donated by Motorola)
| • | Actuation: Two small 60 cent DC motors with lead screw transmission.
| • | Sensing:
| • | IR proximity sensing
| • | crude force/torque sensing using IR
| • a | joint angle position sensing (potentiometers) |
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| • | Inter-module Communication: Global synchronous communication (Motorola SPI
with RS485 drivers) between 68HC11's plus local IR communication between
adjacent modules. |
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Power is supplied
by the second type of modules called Nodes. Nodes are rigid cube shaped
modules roughly 2"x2"x2" with 6 connection ports whose
main purpose is to hold gel-cell batteries and to allow for non-serial
chain robots. |
By the time Mark graduated in Dec. 1994 he had 11 modules total.
The structure is a essentially two four bar linkages attached by two other links with an added sliding bar constraining four of joints in the two four bars to remain colinear. The two degrees of freedom are not exactly a prismatic degree of freedom and a revolute degree of freedom, but it is easy to intuitively think of it that way. The revolute degree of freedom has a range of motion of +45 and -45 degrees, and the prismatic degree of freedom can change the length of the module from about 1 inch to 2.5 inches tall.
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Last updated February 21, 2000
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