Research Abstracts - 2007

MultiShady

We are interested in self-assembly for truss structures, which has led us to investigate a new kind of self-reconfiguring robot system that is a generalization of our Shady truss climbing robot. MultiShady [1] extends the Shady system to support an arbitrary number of cooperating Shady robots plus a set of passive bars which are not connected to the environment. Both the bars and the Shady modules are free bodies—the bars are simply unactuated rigid segments which are free to move under the power of one or more Shadys. Thus, MultiShady is a heterogeneous self-reconfigurable modular robot with two types of module (i.e. it is bipartite).

Research Context

Some other reconfiguring robots are also truss-like, and some are bipartite. TETROBOT [2] is a manually-reconfigurable truss-like robot based on linear extension of the truss segments. The Molecule [3] has male and female modules and is thus bi-partite. SOLAR [4] is a modular system composed of passive struts, which can be configured into 2D trusses by robots operating on an air hockey table. Self-assembling and self-reconfiguring truss systems can be a promising direction for robotic assembly of large structures in space [5].

Simulation

We have begun development of a simulator for the MultiShady system, called MultiShadySim. Several stills and animations from this simulator are shown below. Passive bars shown in gold, and the long horizontal bar is considered fixed in a world frame. Shadys (blue) have two distal rotating grippers that grab bars. The MultiShady system is a fully capable 2D self-reconfigurable robot: it can change topology (and hence, aggregate shape) without manual intervention, as this tower self-assembly sequence shows:

MultiShady constructions may also be mobile even without changing topology, i.e. they may act like actuated linkages:

Many topological structures are possible:

Next Steps

While the MultiShady concept does not require any change to Shady's kinematic structure, it is unlikely that our current prototype single-Shady hardware (under development) will have the power to perform interesting MultiShady activity. In the future we may develop new hardware with such capability.

MultiShady is not the only possible formulation for multiple interacting Shady-like robots. Notably, though, this model does not require any modifications to the original Shady kinematic structure, at least for a planar implementation in which the segments and the links exist in (fixed) parallel planes.

References:

[1] Carrick Detweiler, Marsette Vona, Keith Kotay, and Daniela Rus. Hierarchical Control for Self-assembling Mobile Trusses with Passive and Active Links. In The Proceedings of IEEE Intl. Conf. on Robotics and Automation, pp. 1483–1490, Orlando, FL, USA, May 2006.

[2] Gregory J. Hamlin and Arthur C. Sanderson. Tetrobot: A modular approach to parallel robotics. In IEEE Robotics & Automation Magazine, pp. 42–49, March 1997.

[3] Keith Kotay, Daniela Rus, Marsette Vona, and Craig McGray. The self-reconfiguring robotic molecule: Design and control algorithms. In Workshop on the Algorithmic Foundations of Robotics, 1998.

[4] Jacob Everist, K. Mogharei, H. Suri, N. Ranasinghe, Behrokh Khoshnevis, Peter Will, and Wei-Min Shen. A System for In-Space Assembly. In Proc. 2004 IEEE/RSJ Intl. Conf. on Intelligent Robots and Systems, pp. 2356–2361, Sendai, Japan, Sept./Oct. 2004.

[5] William Doggett. Robotic assembly of truss structures for space systems and future research plans. In IEEE Aerospace Conference Proceedings, Mar. 2002.