[Matt H.]

Physics Content:
1 Newton=0.225 lbs
As such, one way to trigger the plates is to push upwards with ~.9 lbs of force.

However, the questions you've asked especially about moving robots requires some additional discussion.
A robot moving upwards has some momentum (P) defined as the robot's mass multiplied by its velocity:
P=m*v
Assume that when the robot hits the button it exerts a constant force F until coming to a stop. Using Newton's second law:
F*delta t=P where delta t is the time required for the robot to come to a complete stop (v=0, P=0).
or
F=P/(delta t)

As such, a robot moving fast (high P) could trigger the button even if it could not produce the necessary force when stationary.