Quote:
Originally Posted by euhlmann
If you'll excuse bad diagrams finger-drawn at 1am, here's how a double solenoid does shifting
A spring is needed since there can only be pneumatic actuation on one side. We wanted pneumatic actuation on both sides, so we used a double solenoid.
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There's some confusion here over the cylinder and the solenoid valve.
The valve has a couple of traits. It can be single or double acting (or more), it can have one output or two (Or more), and the internal spool (Slidy bit that does the air shifting) can have two positions or more. You can have any combination of these traits.
The cylinder itself has a different set of traits. It can be double acting (You need air to move it out, and back) or single acting (You need air to move it out, but it springs back), or even reverse single acting (It extends via spring, but retracts with air pressure). You may have one, and only one of these traits. (Well, there are 3 position cylinders, but we're not talking about them)
When a valve is single acting, it has one little coil that's energized by an outside voltage. That shifts the spool inside, and sends air to a different output. When the voltage goes away, the spring returns the spool to the default position, and redirects the air.
When it's double acting, it has two little coils. Applying a burst of power to one shifts the spool in one direction and it will stay there until a burst is applied to the other side, which will shift it the other way.
A single-acting valve is used where you want a item to have a default position, like an arm that must be retracted at the start and end of a match when your robot has no power. The spring will move the spool in the valve to the default position, and route air to the retract of the cylinder, so when you lose power, it will retract the arm.
A double acting valve is used when you want to keep the position of an item after a power loss. Once the burst of power has been applied, the spool stays in place until a burst moves it the other way.
EITHER ONE OF THESE VALVES CAN BE USED WITH ANY TYPE OF CYLINDER
If you have any questions, I'd be happy to answer them for you. If you'd rather keep them private, feel free to send me a PM.