Re: 2013 running 2 - VI air compressors legal?
 

A proper Q/A is probably in order, but let me test the waters here first:

The offboard compressor must be controlled by the robot as if it is on the robot. The benefit of it being offboard is that its weight is not part of the robot. I.E. it is NOT part of the robot.

Here is my question: Can you have the newer, smaller compressor, on your robot (used during matches to keep your air supply topped off) but use the older, larger compressor offboard to fill your tanks between matches? This would be accomplished by disconnecting the leads from the onboard compressor and connecting them to the offboard compressor and using the existing sensors and power supply. The robot is always receiving air from one and only one compressor.

There are three reasons for this:
1. As Jimmy already pointed out, a robot with a substantial amount of stored air can take a long time to refill. While this shouldn't be an issue in qualifying, as you go deeper into elims, time is less between matches. There is a significant difference between the time it takes the two types of compressors to fill large quantities of storage tanks.
2. The smaller compressors get REALLY HOT quite quickly. Even the larger ones get pretty darn hot after a few minutes of continuous run time. The ability to use two compressors saves wear and tear on both.
3. I've been near a robot that had a brass fitting burst because it was connected to the compressor which got so hot the brass softened and couldn't handle the pressure. Not a catastrophic failure like the plastic tanks, but still quite dangerous.

Kev

Re: 2013 running 2 - VI air compressors legal?
 

The issue of spares is what really drives my disdain for this rule.

If I can switch compressors and batteries because spare parts are allowed, then apart from annoying everyone unnecessarily, all this rule accomplishes is to mandate that the cRIO controls and robot's power distribution system be used. That is unnecessary from a practical point of view, because there are plenty of simple mechanical devices (fuses, pressure switches, regulators, etc.) that can control the system without human or computer intervention—and the pneumatic ones are required anyway! Mandate a proper fuse/breaker on the compressor, and that failure mode is mitigated, without resorting to full robot control.

This rule should not exist in its current form, but it does—and with great regret, will be enforced vigourously.


Are you sure that was the failure mode?

Re: 2013 running 2 - VI air compressors legal?
 

For every design decision we make, we have to weigh the trade-offs. Why is "our tanks have so much capacity that we may not be able to fill them between elimination matches; is that worth the risk?" any different than "we can't figure out how to make room for both floor pickup & climbing on the bot; which is more important?" Whether we like any particular rule or not, some (most? all?) of them are there (at least in part) to help level the playing field.

Re: 2013 running 2 - VI air compressors legal?
 

Of course we don't agree, but every other team at your event expects, no demands, that every robot be inspected to the same standard so that they can be sure they are not competing against a team that has an advantage, of any kind.

I did not make that argument. The rules state the compressor must be controlled by the cRio and robot battery.

While the choice of power source is debatable, the cRio still needs to be powered by the robot battery and so does the control for the compressor.

Your telling me it is safe does not make it safe. I can assure you that inspectors find unsafe conditions on robots regularly at every event. While opening the relief valve can be a quick fix, why should the event staff, the refs or other teams be forced to endure this match after match.
T06 & T08 are extremely relevant and provide the basis for inspection and the remedy. If you use something on your robot during the competition, it must be inspected. If you use it without it being inspected, you are in fact, not inspected. The remedy is no points for each match you are scheduled for and a Red Card for the entire alliance if you enter the field and the match starts.

The intent of "one and only one" in no way can be interpreted to mean more than one. If your one compressor should fail, a spare may be installed and that also should be inspected. It is the reason the inspection staff is on duty all weekend.

To reiterate the procedures for everyone to understand, the LRI, Head Ref and FTA act as a group when something that will affect a team occurs. If the LRI finds that a team has an issue, he brings it to the Head Ref and FTA for discussion. If the Head Ref sees an unsafe or questionable part on a robot, he calls in the LRI and FTA if needed, for discussion. If the three key volunteers still cannot reach consensus, each of us has the phone contact info for higher authority. Each one of the key volunteers is tasked with keeping the event safe, operating within the rules of the tournament, for the enjoyment of all. We take that task very seriously.

The incident that Kevin related above occurred at the Midwest Regional in 2011. A team trying to find an air leak had bypassed the compressor control to keep the compressor running. The heat buildup caused a failure of the tubing and fitting at a brass junction. The failure sounded like a gunshot and any pieces were contained within the robot.

Re: 2013 running 2 - VI air compressors legal?
 

Precisely what my point has been all along. At least some LRIs are capable of understanding reasonable thought. I have never argued that the rule somehow isn't the rule and that I don't need to follow it. I'm arguing that the rule is baseless and silly, and achieves nothing in terms of increasing safety or levelling the playing field.

Again, show me how this provides me a tangible advantage of any kind, and I will concede this point. Of course we should all be inspected to the same standard.

So, you're using the rule to justify its own existence? My argument is that there is no need to require the cRIO to be the one controlling or powering the compressor.

What have I said that suggests I don't want my compressor setup inspected? It SHOULD be inspected, the rules are currently needlessly restrictive is all. IIRC the inspection checklist has an item for inspectors to check which reads something to the effect of "turn on compressor; does it shut off automatically at 120psi?". I'm certainly NOT championing for the removal of such an IMPORTANT safety check.

If "one and only one" can in no way be interpreted to mean more than one, then spares are not allowed. I think we can agree that since that is clearly not the intent of the rule, it must mean that we are not to be using two or more compressors in parallel to speed up the process. This serves the goal of leveling the playing field and I agree that this rule should be continued but have its wording clarified such that its intent is clear.

So a team testing their robot in a manner that involved purposefully bypassing at least two safety interlocks caused a catastrophic failure of a robot part by overstressing it. THAT seems like a legitimate safety issue, which I'm sure the Safety advisors at Midwest 2011 spoke to the team in question about.

Re: 2013 running 2 - VI air compressors legal?
 

I thought that when we switch batteries we were required to drain the tanks? That way the tank is filled with the battery we compete with and there's no unfair advantage for using large reservoirs.

There's no obvious place I can find this in the rules though. It says robots are inspected before entering the filler line and robots can't be worked on while in the filler line, so maybe that means robots are in inspection state entering the filler line? Inspection state is powered down and tanks empty.

Re: 2013 running 2 - VI air compressors legal?
 

There is no requirement to use the same battery you compete with to fill the tank.

There is also no requirement to show up for queing in "inspection condition" with empty tanks.

Re: 2013 running 2 - VI air compressors legal?
 

It looks like we're arguing for the sake of arguing.

A rule is a rule, no matter what you think of the rule.

If you have a problem, then Q&A is the ONLY LEGAL way to remedy the problem.

Personally, I don't see the big deal in the rule. Sure, it would be nice to have two compressors on board, and sure it would be nice if we didn't have to use the cRIO to control an off-board compressor, but the fact is, the rules tell us what we have to do.

If one compressor cannot achieve what your robot needs, maybe you need to design a better robot. We (364) are also having pneumatic's woes... 10 pistons, 4 air tanks, and 1 itty bitty compressor... but guess what, that's not stopping us. The system works quite well, and we have optimized our control system to only use air when absolutely needed.

We've never had a compressor burn up, and we have used the heck out of the two on our t-shirt shooting robot (not FRC, so that's why we have two). They're 6 years old with hundreds of hours of use and will still happily charge up our 4 gallon tank to shoot t-shirts over 300 feet. Do they get hot? Heck yea they do! But that's the umm... consequence? of compressing air.

Basically, I don't see what the big deal is.

Re: 2013 running 2 - VI air compressors legal?
 

Ken,
There currently is no rule that requires you to use the same battery for both purposes. At one time this was the rule and you could only fill tanks after your robot was on the field. I ask teams to not pressurize tanks in the queue as I know that teams regularly are writing code and deploying while waiting to take the field. I have seen on numerous occasions, teams checking new code and having the robot move while in the confined spaces in the queue. In the interest of safety, I will continue to remind teams of the possibility of injury even though no rule yet exists.

guy,
If you don't believe that the cRio could or should be the only control for the compressor, what are you suggesting? If the compressor rules are unduly restrictive, what other rules meet that same criteria in your mind?

Re: 2013 running 2 - VI air compressors legal?
 

Back in post #13, I offered an alternate wording to the rule that would be less restrictive.

In essence, what I'm suggesting is that any method of charging your tanks to 120psi which uses an otherwise legal Thomas or Viair compressor that would meet the 1.05cfm rule, includes a working pressure-based shutoff calibrated for 120psi (ie. the Nason Pressure Switch that we've been using for years) should be legal, regardless of its power source (robot battery or otherwise) and control system. You could even skip the requirement that it be an otherwise legal compressor, but that keeps it easy to inspect.

The simplest such system would be to wire the NC Nason switch in series with the power to the compressor through a fuse from a 12V battery with sufficient current capability. I realize that the reason this is disallowed on our robots is because the startup current of the compressor exceeds the current rating of the Nason switch and so runs the risk of failing the switch in the closed position. I agree that this exact configuration should be outlawed for that reason.

However, there is no reason that a similar pressure switch that DOES have the proper current rating couldn't be used in this way.

Alternately, the system which our cart had, which was:
In essence, using our cart was like charging my robots air tanks using a compressor mounted on another robot that otherwise complied with the pneumatics rules.

We didn't, but you could even take it to the next logical step, and have the cart have more storage tanks on it than the robot, which you could pressurize ahead of time and simply dump into the robot, allowing for a nearly-instant fill (assuming you were smart about how you used release valves in the circuit).

My logic behind all of this is that since we all agree that we can change batteries after charging the tanks, the source of 12V power becomes irrelevant to the equation, provided its safe, and since we all agree that I can put my robot on the field with 120psi in the tanks, the method by which the 120psi gets there, and the time it takes to do it is irrelevant, provided its safe. The 1.05cfm limits how much air I can compress DURING the match to about 2.36ft^3, but the unlimited number of storage tanks and the fact that I can start the match with them pressurized to 120psi makes that 1.05cfm value unimportant to the total cubic volume of air I can use in a match.

Re: 2013 running 2 - VI air compressors legal?
 

Please stop arguing with Al. He is the lead robot inspector. What he says (and the manual), goes. Bottom line. It doesn't matter if you don't like the rule. You need to follow it.

Re: 2013 running 2 - VI air compressors legal?
 

Since you asked, Say Rookie Team 9999 doesn't have numerous batteries to bring to competition due to this being their first year. Deep into the elimination rounds batteries are running slim. They have 2 completely charged batteries left. They have a slight pneumatic leak and there is a referee huddle going on at the end of the previous match. The pneumatic system is slowly leaking and the team is concerned they won't have a successful auto mode because their shooter is pneumatic fed and the on board charger won't be able to adequately charge the system enough when the match starts. They can't risk draining their battery either prior to the match to top off their system.

Meanwhile, Veteran team with an off board compressor on their cart doesn't hesitate to recharge their system during the delay because it isn't effecting their match battery at all.

That seems to be a large advantage to me. Just follow the rules.

Re: 2013 running 2 - VI air compressors legal?
 

If 9999's alliance partner 340 were to hand 9999 a fresh battery from 340's stash, so that they could switch before the match, would someone be breaking the same rule?

More to the point, not every imbalance is a rule violation.

Re: 2013 running 2 - VI air compressors legal?
 

So I guess the high pressure N2 bottle to charge the air tanks is out? :)

Re: 2013 running 2 - VI air compressors legal?
 

You know, I think that's actually why FIRST doesn't want us using external air supplies—they're (rightfully) afraid of someone mishandling scuba tanks.

(Which brings me to a prior discussion on this topic that may be relevant.)