pic: Compressor Backpack
 

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Off season project: T-shirt cannon. :eek:

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Who you gonna call?

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We disassembled our t-shirt cannon rally robot last season. We have plans for a new and improved one!

Are you suggesting we also make a hand held backpack T-shirt cannon?

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Looks like a Proton pack from Ghostbusters.

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You might want to ask a Q&A about using the backpack off field at an event.

Per rule R68, one and only one compressor. My Lead Robot Inspector interprets that as: Only one compressor at the event. A second compressor is allowed in the pit as a replacement part.

I know if you are at my event, you would not be allowed to use it.

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We understand the limitations of compressing at an event, but we'll ask those involved with running each event we go to if they have a problem using it at all, even if we leave the venue and charge outside. Chances are that they won't allow it any way or place, but being able to charge tanks before matches with this pack would be so great if it could ever happen. This contraption is primarily for practice and demos anyway.

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Don't even get me started about this...

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How do you mean?

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Dude robot inspectors are 10/10 dabes

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At an event (even on the practice field), the air has to come from the one compressor. You can't bring in air from the outside.

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I have been lucky enough to not have to deal with it, but I have friends on other teams who have come into issues regarding the rules about air coming from one compressor, having other compressors in the venue, and LRIs making up their own opinions about rule intent.

sorry to derail

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Use the Q&A to get a ruling you can print and bring to the event.

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Regardless of legality, this thing is just cool.

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I think we may be able to get away with this at some events IF we only use it to compress when testing systems in the pit and practice field. This could actually be useful for the practice field, due to the limited time.

But we have to remember that we need to compress with our single on board compressor before an official MATCH to make sure the matches themselves are all done by the book.

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This might help you.

If you have a large air tank off the robot and use the robot compressor to fill it the morning of the competition, you could then use air from this tank to pre-fill your onboard tanks before each match. This would still meet the requirement that all air comes from the one compressor and allow you to hit a higher psi before starting your compressor to finish filling the tanks.

I do not believe there is a rule stating that air cannot be temporarily stored off the robot.

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ONE Vent Plug venting ALL stored pressure, even off board pressure.

Now, if you use Quantum Entanglement to activate a vent on the off board tank, I wonder if that would violate the no other wireless communication rule.

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R74 and R75 provide (only) two methods of using an off board compressor, illustrated in Fig. 4-8 and Fig. 4-9. Neither of these permissible methods includes off board air storage.

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R70:
Emphasis mine.

Honestly, this backpack scares me from a safety perspective. What happens to the unlucky person wearing it if a tank should explode? As an LRI, I would insist it be removed from the venue, and I bet the UL Safety advisors would agree.

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This. This times all of it. As a participant at an event I would want that removed. Plastic air tanks scare the bejesus out of me, mostly because I know first-hand how much energy and how much shrapnel they make.

If the pack got dropped while it was pressurized really bad things could happen. Please do not use this device, ever. I know it seems cool, but it's just asking for a disaster.

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It's really, really cool in concept. Pretty much anything turned into a backpack is pretty awesome, and you've obviously made something that serves a very good purpose. I agree, though, about the safety problem. Nobody can stop you from using it in your shop, but i'd suggest using metal air tanks for something like this.

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I agree with Jon.

At LRI training at HQ in early Jan, one of our fellow CMP LRI who works at an Army Testing Lab hired an intern to test the most common plastic tanks available to FIRST teams. The results for the black Clippard tanks was good. The white Clippard tanks (See the Manual for the exact p/n) were ruled illegal after several failures during the season and the resultant testing this summer at the Army Lab. And if I remember right, the performance deteriorated when damaged, nicked or abused, even slightly.

Kudos for thinking outside the box, but you won't see one being used on my team or at my event. Period. End of story.

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You beat me to it Jon. Those white tanks fail regularly if even slightly nicked or damaged. I saw one go off last year on the field and it sounded like a grenade going off. The plastic shards from an exploded tank would be a hazard not only to the wearer but those around him.

That looks super dangerous.

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I was just thinking about this last night, and we should at least encase the entire pack in a sheet of some thick polycarbonate, or some other method of keeping everything inside the pack in the event of any catastrophic failure. We should also replace the tanks with their metal equivalents.

I did mention that this pack is unfinished, and still requires some more safety features. We just needed something built to use for practice, and plastic tanks are what we had on hand.

If this is ever used, it is easily depressurizable for wearer movement to help reduce any accidents. This is only intended for use in safety glass areas around the robot when the robot is running and only when it is needed.

Having a member of our team walking around an event with a pressurized pneumatic backpack is just plain idiotic, and is not our intent with this system.

We don't intend to keep it pressurized for any extended length of time; only when we need to repressurize the robot for practice or testing.

Perhaps a tankless backpack may be the best option for safety, so pressurized air does not get stored in the pack at all.

If we deem this pack too unsafe still, we will make sure to keep it out of an event. Thank you all for your concern. I'm also all about safety, and I want to do my best to help make this pack safer for my team members and every volunteer, student, mentor, and attendee at an event, if that's possible. :D

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It's a great out of the box idea, so you should feel great about that.

I think you got great rules feedback, with some redesign and some Q&A responses you'll have a working system. Metal tanks, shroud, etc are the first steps.

Remember, they laughed at Einstein, and now he has a field named after him.

You can always display it as a "future project" at events. Without air it's not a safety problem

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If you he seen the videos Dana, myself, and the rest of the LRI's saw at training, you probably wouldn't think some lexan would be enough. When these things go off, there is a huge amount or force and speed behind them.

I also want to add that directly connecting it to a battery, as it appears in the picture, is extremely dangerous and could very easily lead to an over-pressurization situation. That's why the rules clearly state the compressor has to be controlled by the robot.

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Team 1746 built a back pack tshirt cannon during the off season for publicity at our school's sporting events (and mostly because I was bored for a few days in class). It's a little heavy and cumbersome but it can fire 6-8 shots per arm and has adjustable pressure for football stadiums vs basketball courts. Everyone at our school loved it and it was really fun to build; i'll try to post a picture of it if I ever get time :rolleyes:

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Again, I have to say that this compressor pack is unfinished and will have a pressure switch and relay. The tanks are being replaced with metal ones. We can opt for a carbon fiber shell if that would be effective, or get rid of tanks altogether. My thought wasn't just "some lexan" but a sheet .25 inches thick, which I think would be enough for high impact, but I'd have to see the videos that you mentioned to really get an idea. My objective at this point isn't necessarily to try to get it "safe enough" for an event, but get it "safe enough" for personal shop use.

I'm open to more suggestions to make this safer for non-event use, since the chances of using this at an event are low, and out of courtesy, it's best to keep it out of the pits and arena at all times.

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Our team made one of these off-board compressor/air pack deals a few years ago. We used a 5 gal. steel tank rated for 250psi and then a FRC legal compressor. We considered all rules and believed it to be legal. We had pressure blow-off's and dump valves on both robot and pack. Big Al promptly ruled it unsafe for numerous reasons.

In retrospect, it was an unsafe idea even though the system worked well at the time and we had built in extra safeties.
Sacrificing safety just to save some time is not the best practice.

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Not to push this, but Al is pretty reasonable, he knows the rules and has helped lots of teams to come into compliance. He really wants you to excel safely. I'm sure he quoted the rules and pointed the way to compliance.

What couldn't you do to fall within the rules?

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I've gotten sideways in this thread.

Let me start over. Lets turn to be a "how can I" vs "you fail" thread. You are smart, how would you make this work?

I want to have a backpack to charge my robot. Assume, metal tanks. Do I need a cable to the robot to control the initial air load? Once the air load is complete, can / how do I load a remote robot?

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Are you talking:

1) in the pit/que right before a match?
2) At a FRC event, other than right before a match?
3) Outside of an event?

#1 is not possible.
#3 anything goes.
#2 is the tricky question.

For #2, I would make a removable air tank pack that can fit into/onto your robot. It should have 2 connections:
1) Connection to robot vent valve
2) Its own vent valve

During practice, you can run with however much weight you want. While you are in que, you can tether and charge all the tanks you want. Or, even bring the robot charged to the practice field.

For competition, you can remove the extra air tanks.

IF you can get the LRI to allow you to run 2 compressors off field, the removable air tank pack could have a 2nd compressor mounted to it (with all the safety stuff). You would then need a connection to a second PCM, to power the 2nd compressor.

Note: At the championship, I forgot if you had to pass inspection in order to use the practice fields. If so, then you can only run on the championship practice fields in competition configuration (without the spare air tanks). However, there were practice areas where I think you don't need to have passed inspection.

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R70 clearly states no off-board air storage. The most you could legally do with this backpack is have a compressor on it that hooks up to the robot to be controlled and to supply air there. And that's only if you don't have a compressor on board.

Even then, I would have some questions about a potentially hot compressor being strapped to someone's back. It would be very easy in that situation to back up, bump into someone, and give them a nice burn to the arm, chest, back, or even face (of the individual was shorter than the one wearing the back pack).

A better solution for carrying around an off board compressor would be something similar to a small toolbox. Put the compressor, gauges, relief valve and everything else in that and it's easily portable and provides some additional Safety from contact with hot parts. You could even get creative, cut a couple of holes for ventilation and power a few fans from a small battery to help keep things cool. Arrange things properly and you won't even have to open the toolbox.

This is, of course, assuming a legal off board compressor set up, with one compressor, no onboard compressor, no storage, and everything controlled from the robot. I don't think using multiple compressors or having off board storage would be legal in any way at an event, even if it was just for pit and Practice field use.

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The only way I can think of to improve this would be to include a miniature Driver Station to tether to the robot and enable it.

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Relevant thread: consequences of one of those plastic tanks letting go. Other legalities aside I'd not want a bomb (and we are talking about energy levels associated with explosives) strapped to my back or the back of anyone else.

http://www.chiefdelphi.com/forums/sh...d.php?t=127956

Edit: on the topic of failure modes...

Even with metal tanks, what happens if a line bursts near the operators head?

What happens if someone trips and falls and the battery starts leaking/spraying battery acid?

I see a LOT of ways for someone to get hurt in some pretty horrific ways for the advantage of having a snazzy, heavy, backpack to charge a robot with air at practice in shop. This is an application where a light-duty shop compressor plus a long hose and/or hose drop would be the right way to go. I understand the appeal of an air-charging backpack, I/my team made one in 2003 to charge our robot that didn't have a compressor, but in hindsight it was not safe and did not get us any significant advantage.

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Turn down for WATT

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We appreciate all of Al's input on our robot, matter of fact he saved us at Milwaukee last year. So we appreciate all of his efforts.

But anyways if I remember correctly it had to do with the diagram in the rule book showing the off board compressor options. We read it as this is "what you need to have" while the rule was "this is only what you could have" off your robot for pneumatics systems. And since there were no tanks in the off board section of the diagrams, the tank was not allowed.

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I would definitely ask it be removed from an event I am a LRI at and if I saw it as an RI I would immediately get the LRI.

I would not allow it to be used on the practice field because we need to maintain equality. If other teams see you using it on the practice field they could easily assume that you use it to charge the tanks on the robot before taking it to the competition field. A RI or LRI can not check and make sure that you do not use it before every match.

Sometimes it is about perception.

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Not all white plastic air tanks are the clippard ones
If I'm not mistaken, the air tanks in the picture are, in fact, from pneuaire, not clippard. Not that that makes it a good idea.

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If the goal is to have a way to charge the tank for practice, it would be much simpler to use a single A/C air compressor than four or more 12V ones.

• Include a tee somewhere in your high-pressure side, just on the tank side of the pressure relief valve so that relief valve will function as a safety.
• For competition, the third branch of the tee will be capped with a solid plug.
• For practice, replace the solid plug with a vent plug, with a quick disconnect on the open end. Keep this vent plug closed except when externally charging.
• To do an external charge:
  • attach the external compressor at the quick disconnect
  • open the extra vent plug
  • turn on the compressor
  • When you reach the desired pressure (or the relief valve vents), turn off the compressor
  • close the extra vent plug
  • disconnect the quick disconnect fitting

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Without commenting on its actual legality, I have personally seen this ruled illegal at events in the past, even for pit use.

Regardless, it is awesome. What are all of the components strapped to? Is that part of one of those auto mechanics creepers or part of a stretcher type thing?

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That is awesome...

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The solution to that safety issue is to put an OPV at every stage of the system, including one at each end of the tank, and set to 65% of the tank's pressure rating. This way, you have a redundant safety mechanism with about a 50% safety margin. With four tanks, you do this to each tank. In the case that a tank does fail, the frame of the pack should be designed to at least somewhat protect the user.

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We put together most of one a year ago on our team, but never bothered to get it firing. You'll probably need some bigger tanks and definitely larger tubing for maximum movability of your barrel.