3 position cylinders

[Racer26]

Originally Posted by craigcd

3 port center port closed solenoid valves were illegal because they trapped pressure and would not allow the full pressure to be relieved. Why can't you add addition pressure relief surge valves to the line to the cylinder and accomplish the same thing? Might be a good question to ask the GDC..

Which is odd, because a center-closed valve doesn't trap any usable pressure. If you closed off a center-stop solenoid (trapping the air in the cylinder to keep the cylinder locked in one position), removed the air pressure from the P port (ie. open the dump valve) and then simultaneously open both sides to atmosphere, nothing will happen, except that gravity might take over, and actuate the cylinder. I think this is another case of the GDC being closed minded and limiting innovation they've allowed in the past, citing a rule intended to provide safety, when their rule arguably makes things less safe.

Center closed solenoid valve would keep a pneumatically actuated arm locked wherever it is, even if robot power or pneumatic pressure is removed. Any other configuration of valves results in a robot appendage that can move when solenoid power is lost (breaker, or field disabled), or when air pressure is lost (dump valve opened). I'm certain many teams can attest to needing to teach their students to be aware of robot actions that can occur when the pneumatic system gains and loses power.