Image of Griffis-Duffy platform made by Charles W. Wampler and Douglas N. Arnold using Matlab. Click for high resolution image.
A Griffis-Duffy Type I platform consists of two equilateral triangles with moveable legs connecting the vertices of one with the edge midpoints of the other. With the base triangle in fixed position and the leg lengths fixed but angles free, a point attached to the other triangle traces out an algebraic curve of degree 40 in Euclidean 3-space. For more information, see A. Sommese, J. Verschelde, and C. Wampler, "Advances in Polynomial Continuation for Solving Problems in Kinematics," ASME J. Mechanical Design, 126:2:262-268, 2004, and the book The Numerical Solution of Systems of Polynomials Arising in Engineering and Science by Andrew J. Sommese and Charles W. Wampler, World Scientific, 2005.