[Racer26]

Originally Posted by Tds123

THis is not true actually u can , u connect a single solonoid to a double solonoid to the piston , if u hooped up the single correctly, it shoudl work just turn that little blue thingy while pressing the double solonoid buttons, the piston wont extend/retract but if u release the blue thing a little the piston will extend/retract the more u release the fast and more it will extend/retract

I'm not really sure how what I'm saying is "not true" since you basically described a similar method to what I did... I have personally built 3 of these type of systems now, with considerable success.

Originally Posted by squirrel

You cannot accurately control the length a piston will extend, if there is a load on it, because the air in the cylinder acts like a spring. You're better off using a motor instead of pneumatics if you need to have good control over how far something moves.

The neat thing about this year's game is that for the most part there is no need to have good control over how far something moves...I mean, the game piece is 40" across, and it just has to go over or under the overpass, it doesn't have to be any specific height. We're using pneumatics that are either up or down for our 3 ball manipulator mechanisms.

While the trapped air in the cylinder can effectively turn it into a spring, I would argue that it CAN be controlled to a reasonable level of accuracy, as evidenced by 1075's 2007 arm. We did however, use, in addition to the ram driving the arm, another ram which clamped down on a piece of Al angle attached to the arm that slid through a piece of Al square tube. This basically functioned as a physical brake, reducing the "air spring" effect.

Originally Posted by Kirk

If you are trying to control the length of a cylinder you want a "center off or center closed" solenoid. Instead of the spool inside moving and staying in position to supply air to port A or port B, when it gets power only momentary to allow air into port A or B allowing for small adjustments of a cylinder. As stated above this can be tricky since the air in the cylinder isn't the full regulated pressure but an average and can act like a spring. If you are interested in these contact SMC and they can help you select the proper one for your situation.

I forgot about these "center-off" valves. My ongoing question about these is "Are they allowed?". Besides, the method I feel I was one of the pioneers of, using a plurality of valves to control one ram fits more within the FIRST mantra of using creativity to solve problems, rather than store-bought parts.