Thanks for all the great ideas!

One very key bit of information I should have included in my first post is
that the DC gearmotor doesn't have to drive the load directly. I can run
the load with a timing belt. Now I can put a spring loaded belt tensioner
against the belt. I can make the spring adjustable and put a limit switch
against the swing arm. If the mechanism jams, the belt tightens and moves
the tensioner against the switch and kills the power. Now I don't need a
torque limiter.