support 206 as bob 208 moves piston 214 suitably slides within chamber 209 formed in bob 208 plug 216 however moves with bob 208 plurality of springs 222 are appropriately disposed between piston 214 and plug 216 such that relative motion between piston 214 and plug 216 suitably compresses and elongates springs 222 additionally bob 208 is suitably supported against housing 230 by a plurality of belleville assemblies in a preferred embodiment three belleville assemblies are preferably disposed at 120 degree increments around bob 208 for clarity only belleville assembly 211 is described belleville assembly 211 preferably includes bolt 220 plunger 212 plurality of springs 224 and plug 210 bolt 220 is preferably threaded through housing 230 plunger 212 suitably pivots on bolt 220 plug 210 rests against recess 232 formed in bob 208 plurality of springs 224 are appropriately disposed between plunger 212 and plug 210 such that relative motion between plunger 212 and plug 210 suitably compresses and elongates springs 224 in a preferred embodiment springs 222 and 224 are preferably bellevilles appropriately configured to exhibit low tangential stiffness and high secant stiffness bellevilles are well known in the art and may be manufactured to provide the requisite stiffness characteristics alternatively standard bellevilles may.