first, you need a clotheshanger, a pair of pliers, some epoxy, and a leaf-spring switch
see pic 1 for materials.
chop a fair bit off of the coathanger with the cutter part of the pliers.
then, you mix up some epoxy
and mix one end of the clotheshanger in it, then stick it to the blade of the leaf-spring
and bolt it onto your robot. tadaa! you are dun dun doneeeee!