Why do we want maneuverability?
A straight line is not always the best way to get from A to B
What do insects do?
Blaberus discoidalis change foot placement (touchdown/liftoff) to alter the moment arm of the horizontal plane force. These cockroaches also alter the leg swing angle to change the direction of the effective force. There is also a small change in stride frequency and force generation from the legs.
(D. Jindrich and R. Full 1999)
What can the Sprawlettes do?
By shifting leg angles towards vertical on either side, a smaller amount of the leg force gets projected onto the horizontal plane, which is key to generating turning moments about the center of mass (COM). This results in a non-neutral moment sum after a complete stride period. The resulting motion is a turn in the direction of the more vertical leg side.
Using the above turning scheme, the Sprawlettes can be commanded to follow or avoid a light source
The duty cycle can be used as an alternate turn strategy. By changing the duty cycle for all legs on either side of the body, the force output of those legs can be altered, in turn changing the moment about the COM for that tripod stance phase.
See Sprawlette#02 in motion. (Video#1)
See Sprawlette#01 in motion, with the NEW 'Sprawl-walker'. (Video#2 Video#3)
What about modeling?
A detailed model of the Sprawlettes has been created in ADAMS
The ADAMS model is being used to develop turn models and design for maneuverability
See ADAMS simulation video. (Video #1 Video #2)
What is next for the Sprawlettes?
A model to characterize the turning behavior
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Related references
Jindrich, Devin and Full, Robert. (1999) Many-Legged Maneuverability: Dynamics of Turning in Hexapods. Journal of Experimental Biology 202, 1603-1623.
Schmitt, John and Holmes, Philip. (2000) Mechanical models for insect locomotion: Dynamics and stability in the horizontal plane I. Theory. Biological Cybernetics 83, 501-515.
Schmitt, John and Holmes, Philip. (2000) Mechanical models for insect locomotion: Dynamics and stability in the horizontal plane II. Application. Biological Cybernetics 83, 517-527.
Cruse, Holk and Silva Saavedra, Manuel. (1996) Curve Walking in Crayfish. Journal of Experimental Biology 199, 1477-1482.
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