<R74>: Each commanded motion of a pneumatic cylinder or rotary actuator must be accomplished via the flow of compressed air through only one approved pneumatic valve. Plumbing the outputs from multiple valves together into the same input on a pneumatic cylinder is prohibited.
How would everyone translate this rule? It obviously means that we can’t connect the outputs of more than one solenoid to a cyllinder, but what about connecting the input of a second solenoid to the outputs of the first solenoid, to control whether or not air can come out of the first solenoid? Would that be legal, or does one solenoid and one solenoid alone have to control the movement of the piston?
I’ll ask a potentially silly question: Why wouldn’t you handle a control mechanism like that in code? Off the top of my head, I can’t imagine a cascade of solenoid valves that couldn’t have their functionality replicated in control code for several independently plumbed solenoids.
I read that as one outputs worth of air goes into each piston. Turning two solenoids into a center-locking valve would still be allowed. However, I am not the GDC.
Ask a silly question, get a silly answer. We are trying to stop the cyllinders mid-stroke, which has turned out to be harder than we originally thought. The cyllinders can be stopped if you stop the exhaust from escaping, with a second solenoid. Otherwise, it’s very difficult to stop them mid-stroke.
Fair enough. That makes a lot of sense. I also think your multiple valve cascade passes muster under the rules. I believe the real concern with having multiple valves on the same cylinder is that GDC wants to limit the flow rate. Your set up wouldn’t violate that.
As a thought, have you considered a double acting valve? That would let you apply pressure to both sides, which should also lock the cylinder, and cut down one solenoid valve.
Just keep in mind that in either case you won’t be “locked” in position. Air does compress, after all.
u cant stop them mid stroke they will always extende if u put pressure to both sides ther is more surfuce area to extend then retract the rod blocks some of the retraction area
if u look at that picture u can see why there is less surfuce area to retract
yes u can plug the exhaust and it would stop somewhat in the middle
Yes, the compressability of air does make it a bit problematic. It does stop, as long as it’s sitting stationary in our shop, with no forces or accelerations acting on it, but in competition, who knows if that will still happen!
You can stop them mid-stroke. It’s been done. It’s been done in FRC.
If you put the same pressure on both sides, the piston may move…
…Provided that the displaced air has somewhere to go. If that air has nowhere to go, then the piston’s motion will stop as soon as the force on each side is equal. Motion will resume as soon as the air has somewhere to go again. By placing a single solenoid on the exhaust of a double solenoid, it is perfectly possible to gain control over where the piston stops.
What i said is still correct if u put the same presure to both sides IT WILL EXTENED. If u plug the exaust then the cylinder compress the air in the side wth less surfuce area untill the forces equilize
i would actually suggest stopping the imput not the exhaust. if you can manage that (and its not as easy as it seems) then you can control with MUCH more precision than stopping the exhaust, considering the cylinders arent made perfect.
That brings us back to the original problem though, because you can’t have more than one solenoid controlling the inputs of one piston, so you can’t have a “stop solenoid”, whether it’s before the primary solenoid, in the feeder line, or after the primary solenoid, in the exhaust line. It’s still illegal, according to <R74>
so the way we have gotten around the lack of center locking solenoids in the past is now illegal. I wonder why they axed this after many years of it’s use?
I have no idea. We have used it before, back in 2008 with Overdrive. I looked back at the 2008 manual, and there isn’t a rule like this year’s <R74>. It doesn’t say anything about having to have pistons work through the movement of air through only one solenoid.
