ABSTRACT
The Bricard linkages are the only 6R overconstrained linkages. Of a total of six types of Bricard linkages, the most suitable ones for the purpose of constructing motion structures is the threefold-symmetric Bricard linkage, obtained by combining the general plane-symmetric and trihedral Bricard linkages. The linkage is mobile because of the plane-symmetric property guarantees it. Although the original threefold-symmetric Bricard linkage can be folded up to a compact bundle, its realisation requires the use of the hinge design. The method to indentify the alternative form of threefold-symmetric Bricard linkage is the same as that for the Bennett linkage. The axes of revolute joints are extended and joints are connected with bars not perpendicular to the axes, where the solid lines present the links of the original linkage and the dashed lines present the bars in the alternative form. Another Bricard linkage found to be useful in creation of motion structures is that with both line and plane symmetry.
