well you deffenety wana make it lock ( i can turn the fischer price moter backwords by hand, so can a 130 pound robot ) the question is how. you could have a purly mechnical oneway rachet idea, or you could have a mechanical/electrical idea with a solonoid ( not a spike ) or a servo even to move a locking pin/bar into place. some other things that spring to mind are a one-way cable slip ( remember in the matrix, elevator sceen ) or even a friction brake.
just some random thoughts, jacob
