For now I'm going with a small electromagnet as end effector.
I should think that measuring motor stall current would be past the point of putting
too much force on whatever is being picked up.
Could you explain your end-effector idea a little more?
Also, with those resistive force sensors, I should think you could mount them between
a thin piece of relatively hard rubber and the metal frame, to pickup transmitted forces.
Eg, glue the rubber down at the 2 endpoints, and slide the force sensor into the slot
between the rubber and metal.