Pneumatic Restrictions & Improvments

[cbale2000]

Originally Posted by Mr V

There have been other causes for tank failures than over tightened fittings. Improper mounting, abrasions, impacts have been documented causes of failures.

The white Clippard tanks have been banned, that is why FIRST sent black Clippard tanks to later events for the free exchange for the white tanks.

I don't recall FIRST ever banning them, just strongly recommending they be changed and offering replacements. Our team was offered replacements for our white tanks on our robot at all 3 of our competitions this season, but we declined since the new tanks cannot be capped off at one end like the white tanks can be (and the layout of our pneumatic system required the tanks to be capped off on one end due to their positioning on the robot). The inspectors never had any problem with this.

Did we all miss a memo somewhere?

Originally Posted by Mark McLeod

That would still be an obvious violation of R79.
If the compressed air is generated and mixed from more than a single compressor, then rule R79 is violated.

Maybe it's just me, but if this is the case, it's one of the most arbitrary and pointless rules FIRST has ever made. There is an obvious advantage (and maybe even a safety issue) with having two compressors running simultaneously, but I see no unfair advantage whatsoever in allowing a team to use a separate compressor to pre-charge a robot prior to a match assuming it is the only compressor running and all the other rules for off-board compressors are followed. It just allows a team to go into a match with a cooler compressor, the same effect which could easily be accomplished by having a fan blowing across the compressor or sealing the system from leaks and charging it a few minutes earlier to allow for cool-down time.

Honestly I think people are lawyer-ing over this too much, its obvious what the intent of the rule is, regardless of how you argue the wording.

Now, granted, this entire issue would be a moot point if the stock compressor was rated for continuous duty like the older ones were, since they virtually never got hot and there would be no need to use a separate compressor to pre-charge the system. If anything it only hurts newer teams by giving them a less effective compressor then older teams can afford to buy.

[RyanShoff]

I wish we could find a way to safely use 3-position solenoids with a closed center. They allow a cylinder to be stopped in the middle of travel.

[Jared]

Originally Posted by RyanShoff

I wish we could find a way to safely use 3-position solenoids with a closed center. They allow a cylinder to be stopped in the middle of travel.

What's unsafe with how we would use them now? It shouldn't cause any sudden changes when you disable. You will likely need flow control valves to slow down the cylinder a bit so you can accurately stop it.

You can have a similar effect with two "FRC typical" latching double solenoid valves. On the first valve, you connect output A to the cylinder, and plug B's exhaust port. You do the same thing for the second valve.

When the first solenoid is at "A", and the second is at "B", the first solenoid pressurizes one side of the cylinder and the second vents.

When that arrangement is switched, (1st on B, 2nd on A), the cylinder goes the other way.

When both are at "A", you get the somewhere in the middle position.

When both are at "B", you get no pressure. Both of these states can be desirable.


The rule as it is now says "one and only one compressor". Karthik is right, "one and only one" means only one.(http://en.wikipedia.org/wiki/One_and_only_one). If you're not using the first compressor to ever put air in your robot, then you're in violation of the rule. There is a single unique compressor that is allowed to fill your robot.


There are a few things that I think are currently unsafe/have room for improvement with the pneumatics system.
1. Teams using valves that aren't double acting. When you go to emergency disable the robot, many things suddenly move. We had a few close calls with articulating wheels in 2012. You'd be walking around the robot when suddenly the laptop controlling it would go to sleep, and suddenly all the wheels would move up and the robot would fall to the ground.

Also, when a ref e-stops you, your single acting solenoids can change state, possibly launching a ball straight into a poor volunteer.

2. The pressure switch. We need a transducer that tells us the actual pressure and we need to be able to use that sensor to control the compressor. The large cycle range of the switch is not ideal for some teams. There are teams whose autonomous program just runs the compressor as soon as auto mode starts. Although the pressure never exceeds 120 psi, they can (and do) fail inspection.

There are teams out there who have their relief valve set below switch pressure. This way, the compressor is always running. A poor solution to a problem that doesn't need to exist.

Our auto mode left us with about 94 psi. It would be really nice to have the option to start the compressor to get us more pressure before our next shot.

This could also give us the ability to refill our tanks between matches without having to let out enough pressure to get the compressor to start.

3. Clarification on "reusing" air. Must we dump all air before we refill for our next match? We've been told yes and no. We've also had four back to back matches where there was not physically enough time to do a full refill.

4. Tiny stupid detail, but if R79 applies to ALL air, then you must use your robot's compressor to fill your pneumatic tires or balloons.

[Jon Stratis]

There was a relevant Q&A to the most recent rounds of questions...

Q209 Q. Rule R79: "compressed air on the ROBOT must be provided by one and only one compressor." 1) We can only use one compressor at a time, but can swap out compressors (e.g. if the one we are using starts to overheat). 2) We can only use one compressor for an entire event. Which reading is correct?

A. Situation 1, but also consider T8 and T10.

T8
At the time of Inspection, the ROBOT must be presented with all MECHANISMS (including all COMPONENTS of each MECHANISM), configurations, and decorations that will be used on the ROBOT during the entire competition event. It is acceptable, however, for a ROBOT to play MATCHES with a subset of the MECHANISMS that were present during Inspection. Only MECHANISMS that were present during the Inspection may be added, removed or reconfigured between MATCHES. If MECHANISMS are changed between MATCHES, the reconfigured ROBOT must still meet all Inspection criteria.

T10
If a ROBOT is modified after it has passed Inspection, other than modifications described in T8, that ROBOT must be re-Inspected.

My interpretation of this is that the GDC is saying that there is nothing inherently wrong with swapping out a compressor, but that doing so could be considered a modification and teams should check with an inspector when doing so. As Al can tell you, we've seen all sorts of things, and it's not uncommon for a team to leave a non-working part on the robot, even after the replacement is on (I've heard a story of a team having a half dozen burned out speed controllers on the robot... perfectly legal, but it's some awfully expensive ballast!). That's one reason why you should get reinspected... to make sure you didn't do anything accidentally that makes your robot illegal!

As Al indicated, there are numerous reasons we have these rules. R79 is really no different than R29 - one limits the number of compressors you can use with the robot, while R29 limits the number of motors. No one would argue that a team couldn't replace a burned out motor, and we shouldn't be trying to nit-pick R79 to death and say that we can't replace the compressor either.

The difference between the two is the way the items work - a motor creates mechanical energy from a supplied electrical source. Cut off the electricity, and the mechanical energy stops. A compressor, on the other hand, creates a reservoir of stored energy for later use - when you turn off a compressor, the energy is still stored for later use. The rules are simply controlling how energy flows within your machine - you can only use mechanical energy from a limited number of motors, and you can only use stored energy from a limited number of compressors (ie 1).

[JB987]

Thanks for finding relevant Q and A we used to guide our decision to have a back up system on hand Jon. Couldn't find it on Q and A forum... finally saw it on PDF And thanks for reminding others of the importance of flowing T8 and 10. Our back up system was mounted with primary compressor so both were inspected at same time. Still hate the vagaries of language when it comes to rules and interpretation and amazed at how many interpretations people can make from the same statement...

[nicholsjj]

I guess the only question I would have in regards to the on and off-board compressors is that is it really out of the realm of resources for most teams to accomplish in a safe manner that would give them any other advantage besides having a cooler on board compressor. Let's say that we could change the rules to teams using an on and off-board air compressor in their pneumatic system as long as both compressors are the exact same cost components and they follows all other pneumatic rules. All the teams would have to add to their system is andymark part am-2186 ($4) to where their current pressure switch is along with am-2257 ($3.50) in order to have a way of plumbing safely to their current system from an off-board compressor. The team could also have to wire their robot to have the ability to transfer their spike's power output from the on board compressor to the off board one as well. The last item a team would need would be the extra compressor, and let's assume that since the team doesn't have the extra resources to already go out and purchase something other than the now First Choice Viair then that will be the one they have to purchase at ($69). I will assume that the team will have extra pneumatic tubing available to plug into the close off valve. So to keep a system that doesn't burn a person's hand when they are transporting the robot on and off the field a team would need less money than what is needed for one double solenoid and the ability to mount a spike where it can power both compressors. Now is their anything I'm missing here that could become a more dangerous pneumatic that before or too much of a competitive advantage that a small team couldn't over come resource or knowledge wise. I just really don't like hot compressors and with short turn around times for teams I think allowing an extra off board compressor to help that situation would be beneficial in fixing that problem.

Note I really respect the decisions by very great people that go into making the rules and I just would like to see if this can get looked at a bit more.

[DampRobot]

Originally Posted by cbale2000

I don't recall FIRST ever banning them, just strongly recommending they be changed and offering replacements. Our team was offered replacements for our white tanks on our robot at all 3 of our competitions this season, but we declined since the new tanks cannot be capped off at one end like the white tanks can be (and the layout of our pneumatic system required the tanks to be capped off on one end due to their positioning on the robot). The inspectors never had any problem with this.

FYI, you can make and "end cap" on the black tanks by taking a short length of pneumatic tubing, folding it over on itself, ziptying it together, and sticking it in the NPT port of the tank. Worked well for us, and didn't leak in the slightest. Plus, it's super cheap.

[AdamHeard]

Originally Posted by DampRobot

FYI, you can make and "end cap" on the black tanks by taking a short length of pneumatic tubing, folding it over on itself, ziptying it together, and sticking it in the NPT port of the tank. Worked well for us, and didn't leak in the slightest. Plus, it's super cheap.

They also sell plugs on mcmaster.