Pneumatic Restrictions & Improvments

[Mr V]

Originally Posted by DampRobot

Please, no!

Plastic tanks are one of my favorite technical developments for FRC in recent years. They make large volume pneumatic systems much, much lighter, and have raised the overall level of competition. There prevalence in FRC speaks volumes to how useful the average team has found them.

The failures in the white plastic tanks that have occurred have all been the result of user error, not defects in the tanks. All the failures that I have seen reported on CD were the result of overtightening the fittings on the white plastic tanks (and there have been no reported catastrophic failures of the black tanks). This problem has already been solved in two ways. First, the black plastic tanks (with integrated NPT fittings, which cannot be overtightened) are being sold, and can be exchanged for the white tanks for free. Second, there's been a great deal of education in the FRC community about the dangers of overtightening these fittings, both through Bills Blog, and these forums. Another possible way to resolve the issue would be through more rigorous pneumatic inspection, or even possibly a FRC-wide phaseout of the white plastic tanks (but NOT a blanket ban on plastic tanks in general).

We deal with a lot of stuff in FRC that's potentially dangerous. Dropped robots could break toes, batteries can leak, drills and saws can seriously injure students if misused, and any number of high potential energy mechanisms could inflict great injury if they failed catastrophically. Thankfully, our response as a sport isn't just to ban anything that could potentially be a safety risk. Instead, we maintain a safety-orientated culture, educate students and mentors about potential safety issues, and deal with potentially unsafe robot mechanisms on a case by case basis at regionals.

The right way to deal with this safety issue is through updated pneumatic inspections and through education to the community. Blanket bans are unnecessarily blunt, and would deprive teams of a great resource.

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.

[AdamHeard]

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.

It's a bummer that many inspectors confuse them for the pneuaire tanks.

[sanddrag]

Originally Posted by AdamHeard

It's a bummer that many inspectors confuse them for the pneuaire tanks.

Which led to my students being improperly told our PneuAire tanks were illegal because they were "the white ones", and my students proceeding to disassemble our pneumatics system prior to inspection....

From this experience, I taught my students that they must be experts of everything (which they were not at the time), and always question the validity of an inspector's claims if they do not agree with our standard practices.

It was a good learning experience.

[Al Skierkiewicz]

Andrew,
The Cv, port size and tubing size are limits placed on design because this is an engineering challenge as much as a robot competition. These limits are in the same group as the limits on size, weight, electrical power source, quantity of motors, etc. They are also in place for those teams that lack a pneumatics mentor to show them proper procedures and safety methods. For teams that have sufficient resources to own more than one of something, you need to always keep in mind that there are a fair number of teams that can't afford even the simplest of parts and tools let alone a second compressor.
As such, I would like to suggest to others reading this thread that items claimed as having been ruled legal at an event or covered by a Q&A response may in fact be not correctly stated. The post may not give all of the available information surrounding that particular event. (see Mark McLeod and Jon Stratis' posts that relates the true info.)
mk.32, two compressors are not legal in 2014 and actually never have been even before we allowed off board compressors. The "one and only one compressor" language is very specific.
We will consider other suggestions i.e. high flow exhaust valves.
Al

[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.

[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.

[Karthik]

Originally Posted by Al Skierkiewicz

Andrew,
As such, I would like to suggest to others reading this thread that items claimed as having been ruled legal at an event or covered by a Q&A response may in fact be not correctly stated. The post may not give all of the available information surrounding that particular event. (see Mark McLeod and Jon Stratis' posts that relates the true info.)
mk.32, two compressors are not legal in 2014 and actually never have been even before we allowed off board compressors. The "one and only one compressor" language is very specific.

Al,

As you prepare for the 2015 season, I think you might want to revise the wording on this rule to make your intent clearer. Based on the comments in this thread alone, there seems to be significant confusion. Maybe it's because the ruling seems to be a bit counter-intuitive in comparison to what we're all used to.

Originally Posted by Jon Stratis

The wording of the rule is straight forward and strict - all of the compressed air in use on the robot during a match must come from one and only one compressor. You can't mix sources between on-board and off-board, or charge halfway with one compressor and finish it off with another.

So a couple of questions for Al/Jon/Mark and any other LRI's on this rule based on what was written and enforced in 2014.

1. Is it legal for a team to alternate between multiple compressors during an event? i.e. Can a team charge with Compressor A after match 1, and then charge with Compressor B after match 7.
2. If #1 is legal, is it legal for a team to charge with Compressor A and then switch to Compressor B halfway during the charge.

Based on my reading of the rules and your posts in this thread, I'm thinking that both 1 & 2 are illegal. However, this runs contrary to how I've seen this rule enforced, and the interpretation of most people I've talked to.

3. If 1 & 2 are illegal, does this mean a team who blows their compressor during an event is now unable to use a compressor for the rest of the event?

This one seems a little silly, but based on "one and only one compressor" language, it makes me think that this team would now be out of luck.

If 1 & 2 are legal, I highly recommend that the wording be changed, so it's clear that teams are allowed to switch between compressors.

Anything we can do to make the pneumatics rules clearer for teams will go a long way in promoting their safe use throughout the competition.

[JB987]

Originally Posted by Al Skierkiewicz

Andrew,
The Cv, port size and tubing size are limits placed on design because this is an engineering challenge as much as a robot competition. These limits are in the same group as the limits on size, weight, electrical power source, quantity of motors, etc. They are also in place for those teams that lack a pneumatics mentor to show them proper procedures and safety methods. For teams that have sufficient resources to own more than one of something, you need to always keep in mind that there are a fair number of teams that can't afford even the simplest of parts and tools let alone a second compressor.
As such, I would like to suggest to others reading this thread that items claimed as having been ruled legal at an event or covered by a Q&A response may in fact be not correctly stated. The post may not give all of the available information surrounding that particular event. (see Mark McLeod and Jon Stratis' posts that relates the true info.)
mk.32, two compressors are not legal in 2014 and actually never have been even before we allowed off board compressors. The "one and only one compressor" language is very specific.
We will consider other suggestions i.e. high flow exhaust valves.
Al

"R79
Compressed air on the ROBOT must be provided by one and only one compressor"

So Al, are saying that no team can have a replacement/back up compressor (possession of 2)...that they must only have one in their pit? As I stated in my last post, we had no on board compressor, we used a legally configured off board set up. We did have a second compressor with same configuration of fittings and spike control available as back up. Air supplied to the robot system for a match was only provided by one compressor.

But out of curiosity, are you saying that anyone who replaced a faulty compressor (even in middle of filling up their system) would not have been in compliance with R79? I find it hard to believe the intent of R79 was to prohibit replacement of compressors and therefore needed filling of system air...of course, without addressing the issue in Q and A we are left guessing once again (which can still happen after an issue is addressed on Q and A anyways )

[Cory]

Originally Posted by magnets

First of all, pneumatics restrictions were lessened by a lot this year. The CV of the valve restriction was removed.

The reason the GDC limits CV is for safety. If we had unlimited CV, and someone were to put their head against a medium to large size pneumatic cylinder, and it is accidentally actuated, the person would die.

I don't think that's the only justification. Any linear puncher this year that accidentally actuated with a person's head near it would kill or maim them...with the failure mode being accidental release of a 1/2" or 3/4" bore piston.

There's any number of things that are legal and are just as dangerous...it has to be at least partially because of fairness or desire to limit pneumatics to a certain area.

[EricH]

A proposed tweak to the rule:

"All compressed air on the robot at any time must be provided by one and only one compressor [that meets the specs in the rules]."

What this tweak does is it allows the use of multiple compressors, but only one can be used to fill the robot and keep it filled. You can HAVE as many as you want on-hand, but if you fill the tanks with one, you have to drain the tanks before filling with another. And, they all have to meet the specs--no shop compressors can be used to fill the robot.

[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).

[nuclearnerd]

Originally Posted by sanddrag

And this is why they should be legal. The only conceivable safety concern I can come up with relating to their use is you can move fast in two directions instead of just one with an open port Anyhow, to the OP, great thread.

Agreed. Without quick exhaust valves, you're forced to either halve the flowrate by running exhaust air back to the valve, or introduce some other mechanism to retract the cylinder - a complicated waste of weight.

I maintain that rules that discourage the use of pneumatics actually reduce safety. I would trust a factory-tested solenoid valve over a gerry-rigged latch holding back hundreds of pounds of spring force.