Pneumatic Restrictions & Improvments

[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.

[Al Skierkiewicz]

Karthik,
It is my understanding of the intent of this rule is that only one compressor be used for competition. If that fails, as in other components, it may be replaced. It is my understanding/opinion that rules are in place to avoid even the hint that one team can have even a small advantage over another.
Eric, that wording was considered as rule verbage in the past. Simplicity was the deciding factor in that decision.
As to the other ideas about valves and holding air, the ultimate result must be to release all stored energy at the end of a match to force the robot into it's minimum energy state for transport. I most heartily agree with designing your system so that it does not move when enabled or disabled. My arm was crushed during an inspection when the arm fell during the power on tests when I asked for the robot to be disabled.
As to the pressure transducer operating the compressor, I came across more than one robot this year that used that method only to find out that the software was programmed to increase pressure above the specified 120 psi during certain conditions. In one case the max pressure was 145 psi. It was caught by an observant ref who doubles as an inspector for some events.
While some of these items may seem like nitpicking, please put yourself in the position of being a team who was beat in a critical match and then finds that the team that beat them had that second compressor filling their tanks or that system pressure was above 120 psi. Oh yes, I just remembered my wife looking at a team in the queue with a battery and some alligator clips asking me "what are they doing over there?" Only to find that there were running the compressor from a robot battery to run the pressure up to maximum before they took the field. When I checked, the pressure appeared to be close to 150 psi before the team opened their dump valve. Of course we reinspected and re-calibrated the pressure relief valve for 125 psi and gave the team a stern warning.

[Michael Hill]

Originally Posted by Al Skierkiewicz

Karthik,
It is my understanding of the intent of this rule is that only one compressor be used for competition. If that fails, as in other components, it may be replaced. It is my understanding/opinion that rules are in place to avoid even the hint that one team can have even a small advantage over another.

I'm not sure why FIRST would try to choose to take any advantage a team has away from compressors. It seems somewhat inconsistent with many other things. For example, the Thomas 215 compressor is also a legal compressor, but costs A LOT more, but is definitely more capable than the standard Viair 90C. There will always be an advantage for teams with more money unless the rules explicitly specify every part, which is unreasonable. We already have a rule in place to limit advantages from more wealthy teams, the BoM cost limit. We don't limit the number of batteries or chargers teams can bring to the competitions, so why limit compressors?

[cbale2000]

Originally Posted by Michael Hill

I'm not sure why FIRST would try to choose to take any advantage a team has away from compressors. It seems somewhat inconsistent with many other things. For example, the Thomas 215 compressor is also a legal compressor, but costs A LOT more, but is definitely more capable than the standard Viair 90C. There will always be an advantage for teams with more money unless the rules explicitly specify every part, which is unreasonable. We already have a rule in place to limit advantages from more wealthy teams, the BoM cost limit. We don't limit the number of batteries or chargers teams can bring to the competitions, so why limit compressors?

Exactly, if the intent of the rule is to prevent two compressors being on the robot at once, then enforce that, but I can't think of any rational reason to prevent a team from using an external compressor to pre-charge a system with another compressor on the robot prior to a match so long as all other rules are followed and only one of the compressors is running at any given time. You're not preventing anything that couldn't be accomplished with a more expensive compressor.

[Richard Wallace]

Originally Posted by Michael Hill

... why limit compressors?

Motor racing would be a different competition if its rules allowed unlimited fuel. Soccer would be a different sport if its rules allowed unlimited substitutions. Launching a competitive new product would be much less challenging if not for (usually unavoidable) limits on budget, schedule, and engineering resources.

Limits are part of the challenge. Without them, life would be boring.

The "one and only one" compressor rule puts a limit, based on rates of air flow and temperature rise, on the energy that can be used during a match by an FRC robot's pneumatic system. Matches might be made more interesting (or even more challenging) if that limit were raised -- but they would surely become less interesting if the limit were completely removed.

[Michael Hill]

Originally Posted by Richard Wallace

Motor racing would be a different competition if its rules allowed unlimited fuel. Soccer would be a different sport if its rules allowed unlimited substitutions. Launching a competitive new product would be much less challenging if not for (usually unavoidable) limits on budget, schedule, and engineering resources.

Limits are part of the challenge. Without them, life would be boring.

The "one and only one" compressor rule puts a limit, based on rates of air flow and temperature rise, on the energy that can be used during a match by an FRC robot's pneumatic system. Matches might be made more interesting (or even more challenging) if that limit were raised -- but they would surely become less interesting if the limit were completely removed.

I don't know...I refuse to believe that this falls under the catch-all "but it's part of the challenge". I'm going to guess 80-90% of the teams are using the same Viair 90C compressor because that's what makes economical sense to them. There are some teams who have the money and are willing to spend it on any advantage they can get, and do with the Thomas compressor. Most teams are not willing to spend that much on a compressor, so that right there is an advantage to teams with more to spend.

[EricH]

Originally Posted by Michael Hill

I don't know...I refuse to believe that this falls under the catch-all "but it's part of the challenge". I'm going to guess 80-90% of the teams are using the same Viair 90C compressor because that's what makes economical sense to them. There are some teams who have the money and are willing to spend it on any advantage they can get, and do with the Thomas compressor. Most teams are not willing to spend that much on a compressor, so that right there is an advantage to teams with more to spend.

But due to the system restrictions (Cv, tube size, pressure, and any other constraints that are or have been applied), that more expensive compressor provides minimal advantage at the point of use--that is, at the cylinders. Sure, it might generate the air faster, and keep the stored pressure up more, and stay cooler, but once the air hits the regulator from 120 PSI to 60 PSI, all that advantage goes away at the working end of the system. I think that's why the compressor restrictions eased, and the air storage restrictions eased: Because those don't affect what happens at the working end of the system nearly as much as the other restrictions inherent in the rules. Guess what? If a team isn't a heavy air user, the Viair does make a lot of sense, both financially and from an engineering standpoint, because it doesn't need to do as much work as if the team is a heavy air user, constantly draining their tanks.

Now imagine if FIRST allowed larger-diameter tubing. I think we'd see a sudden run on the Thomas compressors, and suddenly every team that could afford them would be running them. Why? Because now you need more air faster. Lots more air, lots faster, and if the Viair compressors can't keep up, then it makes sense to use better compressors.

[Michael Hill]

Originally Posted by EricH

But due to the system restrictions (Cv, tube size, pressure, and any other constraints that are or have been applied), that more expensive compressor provides minimal advantage at the point of use--that is, at the cylinders. Sure, it might generate the air faster, and keep the stored pressure up more, and stay cooler, but once the air hits the regulator from 120 PSI to 60 PSI, all that advantage goes away at the working end of the system. I think that's why the compressor restrictions eased, and the air storage restrictions eased: Because those don't affect what happens at the working end of the system nearly as much as the other restrictions inherent in the rules. Guess what? If a team isn't a heavy air user, the Viair does make a lot of sense, both financially and from an engineering standpoint, because it doesn't need to do as much work as if the team is a heavy air user, constantly draining their tanks.

Now imagine if FIRST allowed larger-diameter tubing. I think we'd see a sudden run on the Thomas compressors, and suddenly every team that could afford them would be running them. Why? Because now you need more air faster. Lots more air, lots faster, and if the Viair compressors can't keep up, then it makes sense to use better compressors.

Depending on how much air you use, the Thomas can let you drop an air tank meaning weight and volume savings. If FIRST were interested in limiting the advantage in this manner, why not put a similar limit on batteries and their chargers?

[EricH]

Originally Posted by Michael Hill

Depending on how much air you use, the Thomas can let you drop an air tank meaning weight and volume savings. If FIRST were interested in limiting the advantage in this manner, why not put a similar limit on batteries and their chargers?

Because it doesn't matter how many you bring (other than in terms of having spares ready to go for any team that needs them, especially your own), you can still only use one. And, the chargers are somewhat limited in practice, though not in quantity.



Yes, there are limits that seem rather arbitrary, and thus rather frustrating. Yes, that is a real-world challenge. (Along the lines of: No, you can't fit that there in the schedule. No, we don't have that kind of money lying around. No, you can't have any brown M&M's in the candy bowl. Yes, you have to be in bed by this time.) And it may be because those limits seem arbitrary that they're likely to stick around. Eventually, I predict that they'll either loosen up even further, or tighten up again on a couple of models. But until then, all the air on the robot has to come from one and only one compressor that meets robot specs. (And yes, that does exclude shop compressors.)

[Al Skierkiewicz]

Originally Posted by Michael Hill

Depending on how much air you use, the Thomas can let you drop an air tank meaning weight and volume savings. If FIRST were interested in limiting the advantage in this manner, why not put a similar limit on batteries and their chargers?

How are you calculating that? The volume specs are not that different that it would allow you to drop a tank. Please remember it is easy to make decisions based on your regional expectations for availability but we do have an international competition here and all parties have to be considered. While many teams are going to the Viair compressors for weight savings, they know the downside of using this compressor is the heat generated and the lower efficiency as the system approaches 120 psi. This is likely a good place to remind teams that at one time, the robot took the field with no pressure on board and had to fill the tanks once the robot was connected to the field. Prior to that, pneumatics were not allowed on FRC robots. There is a limit on batteries if you think about it. (12 volt SLA/AGM, 18 AH to be charged at no greater than the manufacturer's recommendation, which is 6 amps or less depending on the manufacturer.)

[Michael Hill]

Originally Posted by Al Skierkiewicz

How are you calculating that? The volume specs are not that different that it would allow you to drop a tank. Please remember it is easy to make decisions based on your regional expectations for availability but we do have an international competition here and all parties have to be considered. While many teams are going to the Viair compressors for weight savings, they know the downside of using this compressor is the heat generated and the lower efficiency as the system approaches 120 psi. This is likely a good place to remind teams that at one time, the robot took the field with no pressure on board and had to fill the tanks once the robot was connected to the field. Prior to that, pneumatics were not allowed on FRC robots. There is a limit on batteries if you think about it. (12 volt SLA/AGM, 18 AH to be charged at no greater than the manufacturer's recommendation, which is 6 amps or less depending on the manufacturer.)

The Thomas fills 13.7% faster than the Viair (1 CFM vs 0.88 CFM), meaning if you would have 8 tanks with the Viair, you can get by with 7 with the Thomas (And I've definitely seen more than 8 tanks on a robot as I'm sure you have in the past couple years).

The limit on batteries you mention is analogous to the CFM and PSI restriction on compressors. We aren't restricted on how many batteries or chargers we bring, but we're allowed to charge more than 1 battery at a time.

As far as I can tell, there have always been 4 basic categories when it comes to robot rules.

Rules regarding safety and damage prevention (i.e., max PSI, wheel treads, bumpers, wire size, etc.)
Rules regarding to the game (max size, weight, motors, etc.)
Rules regarding to interoperability with the field (requiring D-Link, CRio, etc.)
Rules regarding to simplification of inspections (Requiring only certain components being used like PDB, Circuit Breakers, Motor Controllers, etc.)

Under none of these categories would the compressor rule fit.

[Jon Stratis]

Originally Posted by Michael Hill

Rules regarding to simplification of inspections (Requiring only certain components being used like PDB, Circuit Breakers, Motor Controllers, etc.)

Those you list here are also safety concerns... Circuit breakers are present to protect the wiring from burning up, approved motor controllers are required so we can know the operating conditions of those controllers in situations like signal lose, and the required PDB to ensure all electricity is routed through proper circuit breakers. I strongly doubt you would want to supply your own PDB, have an inspector say "I've never seen that one before, I need you to take it off the robot and open up the housing so I can inspect it and ensure it's safe".

Believe me, if we didn't have those items required and provided in the KoP, you would see a LOT more robots going up in smoke on the field!

[Jared]

Originally Posted by Michael Hill

The Thomas fills 13.7% faster than the Viair (1 CFM vs 0.88 CFM), meaning if you would have 8 tanks with the Viair, you can get by with 7 with the Thomas (And I've definitely seen more than 8 tanks on a robot as I'm sure you have in the past couple years).

This is not true for operating robots.

Your quoted CFM specs are at 0 psi. The Thomas is not even rated to go to over 100 psi. Reading the specs at 80 psi, the Thomas will fill at .33 CFM, and the Viair will fill at .45 CFM. Above around 50 psi, the viair is faster.

The Viair is more efficient at higher pressures than the Thomas, but the thomas is better at filling empty tanks. The Thomas was never designed to go over 100 psi, so the efficiency drops off really quickly.

Team 358's test show that in the last 31 seconds of run time to fill tanks, the ViAir added 18 psi, but the Thomas added only 8 psi.

If you do some testing with the ViAir, you'll discover it's actually a pretty good compressor if it is kept cool.

[Al Skierkiewicz]

Michael,
You forgot to include engineering challenge rules which the battery, compressor, weight, size, motors and other limits etc. fit into.