Behaviour Of Single Solenoid Pneu. When Robot Disabled Legal ?

[de_]

With a 2 solenoid 5 port valve (ex SMC SY3240) , when the robot is disabled, the internal valves will not change state (even though power is off to both valves). The valves only ever change state if power is applied to solenoid that was not last powered.

With a 1 solenoid (spring return) 5 port valve (ex SMC SY3140), when the robot is disabled....

- if the solenoid was currently NOT energized -> the port that is currently pressurized will continue to be pressurized (ie nothing changes)

- if the solenoid WAS currently energized -> it will no longer be, so the internal valve spring will switch the internal valve to the other output port and dump the air in the current port so the pneumatic cylinder will change state.

Is it acceptable from a FIRST rules and safety perspective that when the robot is disabled, the air cylinders move to their "power off" (ie disabled state) (ie move as a result of the disable command). If not, it sure looks like single soleniod valves can't be used in FRC.

Thoughts ?

[IndySam]

It is common practice to use that situation for end of match actions. In 2007 teams used it to move ramps/lifts at the end of the game and last year teams used it to make a robot hang after time expired.

As long as the action initiated is safe for field reset crews, refs and players, they should be deemed safe.

[Joe Ross]

Make sure to consider the safety of the mechanism when working in the confined space of the pit. Think of how unexpected it would be to e-stop the robot and have something move because of the e-stop.

We had a few places where we would have liked to use single solenoids this year, but decided against it because of that issue.

[Mr. Lim]

Yup...

So, if you have a pneumatic claw powered with a single solenoid, and you are disabled for any reason (i.e. a short communications drop-out, or undervoltage), you risk dropping your tube.

The only thing we've put on single solenoids are our mini-bot deployment latches which one released, don't matter if they return in the disabled state.

Despite the cost of needing 2 solenoid outputs to control them, double solenoids are your friend for the exact reasons you mentioned.

Also they are nice at maintaining the states between power-ups and power-downs.

[de_]

Thanks for comments.

- since it appears to be legal, yes it looks like the issue comes down to safety issues. If we have to stay with what we have, we could put a removable guard around the claw to keep people away from it both in the pit and on the way to the field.

fyi: We used singles as we would have to have spent $140 to get another 9472 card for C-Rio or put a ton of spikes (with all their 12v and pwm wiring).

Too bad you can not daisy chain the spike power feeds of spikes running solenoids together in one feed versus having to use independent 12v feeds and breakers for each 0.5 amp draws)

I do believe that in the past FIRST was suppling single solenoid valves in the kit (as we have 4 Festo singles and a couple of blue other brands in inventory that I am pretty certain we did not purchase).

[DonRotolo]

Originally Posted by de_

- if the solenoid was currently NOT energized -> the port that is currently pressurized will continue to be pressurized (ie nothing changes)

Be careful here. There was a Q&A response that stated something to the effect that the vent valve must vent all pressure in the system. I may be wrong here (I frequently am!) but just double-check that it's OK.

Note: I did see a Q&A response stating that 'center off' valves were OK, so I am somewhat confused here. Again, a frequent occurrence...

[de_]

Originally Posted by DonRotolo

Be careful here. There was a Q&A response that stated something to the effect that the vent valve must vent all pressure in the system. I may be wrong here (I frequently am!) but just double-check that it's OK.

Note: I did see a Q&A response stating that 'center off' valves were OK, so I am somewhat confused here. Again, a frequent occurrence...

I am hoping you are referring to when the 120 psi air dump valve is (manually) openned, no cylinders can be left pressurized. It will do that for both 2 soleniod and single soleniods valves (at least what we use) so we should be okay there.