Quote:
Originally Posted by viggy96
So is a single solenoid just "open or closed"?
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Yes, there's no such thing as an in-between steady state position with a "normal" (single-stage) pneumatic actuator; there are only two steady state positions. To give an example, let's look at the Bimba original air line cylinder. This cylinder has two input ports, one at each end of the body, and can either be fully extended or fully retracted based on which input is connected to pressurized air (typically 60 psi in FRC). The other input must be vented to room pressure in order for the cylinder to move (if you apply 60 psi to both inputs, there's no force being applied!).
To make this happen, a typical valve used in FRC actually has 5 ports:
- Pressurized air inlet (usually labeled "P")
- Output A (usually labeled "A")
- Exhaust A (usually labeled "EA")
- Output B (usually labeled "B")
- Exhaust B (usually labeled "EB")
Let's call the two steady states "Dir A" (e.g. extended) and "Dir B" (e.g. retracted). Note this is notional.. you can make extended Dir B and retracted Dir A based on how you hook the valve outputs up to the actuator inputs.
In "Dir A":
- The Pressurized air inlet is connected to Output A
- Output B is connected to Exhaust B
In "Dir B":
- The pressurized air inlet is connected to Output B
- Output A is connected to Exhaust A
By connecting a 5-port valve's Output A and Output B to each input port of the cylinder, the valve actuates the cylinder either fully extended or fully retracted by routing pressurized air to one side of the cylinder and routing the other side to room pressure (exhaust). Switching the direction of the valve results in moving the cylinder in the other direction.
As previously stated, the only difference between a "double" solenoid and a "single" solenoid is how you command the direction of operation of the valve.
- "Single" solenoid has one coil. Coil=0 --> Dir A, Coil=1 --> Dir B
- "Double" solenoid has two coils (let's call them "Coil A" and "Coil B"). Energizing coil A moves the valve to Dir A; energizing coil B moves the valve to Dir B.
I also want to mention that multi-stage cylinders do exist; they work by having one or more inputs per stage, but each stage only has two steady state conditions (either fully extended or fully retracted).