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Unread 26-10-2016, 11:13
Abrakadabra Abrakadabra is offline
Here We Go !!!
AKA: Scott Kukshtel, Mr. K
FRC #3467 (The Windham Windup!)
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Join Date: Jan 2007
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Questions about operation of pneumatic valves

We are using the standard SMC double solenoid valve sold by VexPro.
We are controlling it using the WPILib DoubleSolenoid Java class.
We are using the controlled piston to hold a latch in place for our catapult.

Issue: When we go over a Stronghold defense roughly, sometimes the solenoid changes state on it's own, with out being commanded by the software (i.e. - the catapult fires)

Further detail: We latch the catapult by pulsing the solenoid in the "forward" direction for a second or two, and release it by pulsing the solenoid in the "reverse" direction, again for only a second or two. At all other times, including when the catapult is latched, the solenoid is set in the "off" position, with the understanding that the valve is piloted, and should hold its last position even when the solenoid is unpowered.

The solenoid definitely switches position, as after the misfire, the latch is fully moved to the unlatched position (and is held there by air pressure). So this is not a case of the latch simply "slipping its grip".

Question 1: Is it possible for a mechanical shock (such as might be caused by going over a Stronghold defense) to cause the unpowered piloted valve to be jarred sufficiently to actually switch positions? Or should we be looking more at the electronics as a possible culprit?

Question 2+: What are the pros and cons of "pulsing" a double solenoid versus just keeping it powered in the desired direction? Would it be possible for 8 continually-powered solenoids on the PCM to exceed the max 500mA current rating of the PCM? (We are only using three right now). Does keeping the solenoid constantly powered shorten its life in any appreciable way?

Thanks for your ideas!
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