[PAR_WIG1350]

I believe I have found a solution to most issues arising from the illegality of exhaust restricting solenoids that has been a hindrance to all plans involving stopping a cylinder mid stroke.
Unfortunately, due to the apparent desire of the GDC to prevent the trapping of air within the pneumatics system,
http://forums.usfirst.org/showthread.php?t=16642
the solution is slightly more complex than it otherwise would be, but that can be worked around.

The solution, in compliance with this years rules is as follows:

1. Connect one secondary regulator per cylinder to be controlled to the 60psi side of the pneumatics system.
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2. Attach a servo to the knob that controls the pressure setting of the secondary regulator.
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3. Connect one port of the pneumatic cylinder to the secondary regulator output (technically, a solenoid is unnecessary, but this seems to make them mandatory, use your best judgement in deciding placement, powering it and programming it are unnecessary.)
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4. Attach an adjustable flow control valve to the second port. Leave it fully open at first and reduce the flow if the spring induces significant oscillations.
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5. Place a variable force device (i.e. a spring) such that it applies force to the piston opposite the force resulting from the pressurized air in the cylinder.
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6. Remember, the restoring force of a spring is kX. where k is the spring constant and X is displacement; and the force of the piston is (Pi*[bore/2]^2)*pressure if the cylinder is extending and (Pi*[{bore/2}^2-{rod diameter/2}^2])*pressure if it is retracting.
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   Set the spring force equation equal to the appropriate pneumatic actuator force equation substituting in the correct values for bore, k, and, if necessary, rod diameter and the desired value for X. For unbalanced mechanisms, account for the force applied by the mechanism in calculations by adding this force to the appropriate side of the equation.
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7. Solve for pressure.
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8. Program the servo to adjust the regulator to the pressure value found using this method.
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Note:constants are red, independent variables (inputs) are blue, and dependent variables (ouputs) are green.

I am not an official source of information, I cannot verify the legality of this method of cylinder control.