[Bill_B]

Retracting the jacking cylinders simultaneously will be complicated by the lengths of tubing and locations of the solenoid valves involved. The longer the path for the escaping air the slower it will travel, much like current in a higher resistive circuit. That said, you may even want one side of the robot to start falling earlier if you're depending on a slight tilt to engage your second rail hook. It's similar to building demolition that sets off the severing charges in a calculated sequence to get the building to fall in a certain direction.

You should be able to devise an small experiment to see if the retraction happens fast enough. Suspend a small ball with an electromagnet. position it the same distance above the table that you want the hook to fall. Devise a single push button switch that releases the air in the cylinder via a solenoid valve AND interrupts power to the electromagnet. It's now a race to see if the ball hits the deck before the cylinder is totally retracted. Repeat observations until you're convinced one way or the other about how fast that cylinder can retract.