Compressor Saftey

Hi Im hoping to use a mini compressor in my feather combined with a pressure switch to run the flipper at 10bar, I realise that i would need an 11 bar release valve but my saftey concearn is over adapting the compressor to connect to the phnumatic system in the bot.
It seems that the least modification would be to aquire one of the commonly avalible male hose tail bspt fittingings to use on the bot phnumatics, remove the tyre valve adaptor from the end of the compressor hose push it on to the hose tail, secure with somthing ( such as a jubillee clip ) and away I go. But will it pass the tech checks for saftey?

If not Im in trouble. We took the hose off completely and a standard 6mm 10bar pipe fit over it. All we then did is fit a home made clamp (tried a jubille clip but didnt have one the right size).

The problem we had was when the compressor ran hot the pipe burst so we turned it down to 8 bar.

I dont see any probs with it and are planning to take it to preston where Ill find out if anything needs changing.

I myself left the Pipe and valve on the compressor and a had a special pneumatic push fit on the end and used the lever from the valve as my Dump valve. This worked extremely well and I never once had a problem in Turbine 3.

An alternative method would be to get some 6mm id nylon tube and get it crimped onto the output of the compressor; this is what Tkm2 do with success; however the tool to do the job is rather pricey just for doing a one off job.

Ill bring some of the brass push fits along to FWS if you are going ask me and ill give you 1. Also I would recommend you get a pressure switch from technobots so when your compressor reaches the maximum pressure of 10bar it will fire a relay to switch of the compressor. Best of luck.

Regards
Dave moulds
Team Turbine/PLF

About safety. If the hose connected to the compressor comes lose,or melts; what is the worst thing that can happen?
In a robot, in the arena.In the worst case you have a constant battery drain, gears turning, and some air flowing.Remove the link, no problem anymore.
The realy badest scenario is simple.Testing at home,and the pressure going to high.A bursting pipe at 300 psi is some shrapnell.Now, if you adhere the safety rules about pneumatics, like fitting a pressure relief valve rated at the right setting.Then even that isnt a problem.

So, the FRA rules protect you even at home.If you follow them.

here is an interesting question I was given by a new roboteer recently. I think it fits well here.

My friend was running a 250psi system, but had a coke bottle as his main bottle. It was filled with compressed air to 250psi by an external compressor prior to sending it into the arena.

His question was, having read the robot wars rules, this system appears to be illegal. According to the rules, he MUST have one of the co2 bottles listed. This means, for seafety reasons he must put 750psi liquid co2 into his robot, as it is not safe to do it his way.

not actually looked into this yet, but it would be pretty funny if this was the case. Anyone know different?

Im not sure if I follow you, James. Having a CO2 bottle doesnt mean you have to fill it with CO2.

no no, I mean this roboteer was bemused by the fact that only 3 or so bottles were legal.
He laughed that he had to put in a 2 kg ali bottle, in place of a coke bottle, and as its in there it might as well be 750psi once you amke the investment.

as I say, its silly, but there are roboteers out there event now with steel bottles for sub300psi systems.

How much pressure can you safely get into a plastic coke bottle? And how do you go about attaching pneumatic fittings? I considered all this a while back but couldnt figure out the technical side of it all. Not considering it any more, but just curious.

-- Kev

the coke bottle, and as far as Im aware, the pepsi bottle, are rated at 300psi. do not ask me how, or why I know this, I just do. Something to do with model sircraft but Ive no idea how the subject came about.

attaching fitting is easy, drill 2 holes in the lid, and screw in pnematic fixings. Use resin to add extra security if you want.

this is a very reliable and lightweight solution, which rex garrod used in his 12kg rexs robot challenge. (although at 50psi)

the best thing about this is, you make the lid with the fittings, and you can attach about 15 different size and style bottles to it, giving you lots of options.

1 problem, you have to drink the coke first, which apparently is bad for you?

I was reading something about these bottles earlier, I think they said they would burst at 14 bar (~210 psi ish). Either way are Roaming Robots likely to allow a coke bottle as a pneumatic part?

FRA rule 8.3.:
The compressed gas shall be stored in a comercially manufactured gas cylinder of appropriate design, specification, and certification. Except where the maximum storage pressure is less than 50psi (3.4Bar).

This raises another question- in the origional Cassius, Rex used an F1 role bar as the basis of the chassis, but also stored 100psi CO2 in there for the suspension. It had no problems containing that pressure (it was thick, high grade steel), and Im sure the whole system would have been implimented safely. Would it still be outlawes under these rules, or is there room for negotiation on this issue- i.e to ask the EO prior to the comp?

hum... we need to test these coke bottles as I have always worked to 300psi.

So with a couple of reasonable sized bottles I imagine you could get a comparable number of same-powered flips as someone on CO2. Or I spose you could use a 500ml bottle as a 10bar buffer tank - that would save some weight.

Id be tempted by FP tho as regulators are expensive :proud:

-- Kev

so are two burkets! id prefer to pay 15 quid for a reg, instead of 140quid for a pair of valves!

Coke bottles would be excellent, cheap, high capacity, large orifice buffers. Still the concept of using soft drinks bottles to stored high pressure CO2 is quite a worrying one on the face of it. Some official input would be much appreciated :-)

...preferably before I shell out £60 on a new buffer tank!

Neil, you only need a PRV with a compressor system if the remaining pressure fittings etc. are rated lower than the maximum potential pressure from the compressor. As for pneumatic connections, it always remains a possibility that nylon tubing etc. can blow off. The safety related consequence of such a failure in the arena is minimal. The risk of personal injury does exist if such a failure should occur during testing / maintenance of the bot - safe working methods should always be adopted. You are encouraged to ensure your build quality is adequate for the purpose, if you bodge the connections, you may still fail a tech check.

James, you are permitted to use non-certified components on systems with pressures up to 50 psi. This rule was included so as not to exclude bots built to Rexs Robot Challenge rules. Above 50 psi, the pneumatic rules apply and that means your coke bottle has to be certified. However, I would suggest to event organisers that coke bottles used at pressures above 50 psi would not be acceptable for a number of reasons. There are no CO2 bottles listed unlike the Mentorn rules, what is required is a suitable vessel in terms of design, specification and certification.

Eddy, yes the Cassius approach is almost certainly unacceptable as the FRA rules require all pneumatic components to be adequately protected within the body shell.

Paul
FRA Techical Team

From what i herd, Coke bottles can only take up to around 100psi before they go bang BIG TIME. I wouldnt go too high in coke bottle. Maybe 80spi, sometimes 100psi, ive found all coke bottles differ, even tho there all created the same way.

Mr Stu

Its quite funny to watch the robot arm pouring liquid co2 into a coke bottle.

All I have to say is BANG!

Are coke bottles tested at time of manufacture. I would guess at yes even if its just for a leak test. If you could find out the test pressure then under the rules (As I see them) they would be acceptable if derated by 20% from the test pressure. You would of course have to be able to provide documentation for it. Anyone out there work in a coke bottle manufacturing plant? Personally I wont use them as they are too easily damaged and the dry powder fire extingusher bottles dont weight that much anyway.

weve taken them to about 110psi, and ran away cos it was getting very hot.

Im testing cokebottles, the 1.5L trow away versions, and they seem very happy with 70 psi.

I would suggest the RRC rule of 50 psi... oh, the FRA did cover that already.
Ok back to square one. Like the original posting told, the FRA rules seem to be very safe.Adhere to them.

I used to run a small coke bottle on 80psi, no problems...Even ran 1 on 100psi once...not at an event though, incase someone found out :) But it worked well and Ive tested a 2littre coke bottle to the bursting point...sort of. I got it up to about 200psi. Scary...The problem is not usually the bottle itself, but the thread on the end or inside the caps stripping.

But Id always suggest a blowtorch bottle as an upgrade from a coke bottle!

Regards
Dave moulds
Team Turbine

Im not sure what pressure the compressor will run to before it stalls the motor but I believe it will be over the 10 bar so I will fit the relief valve to be safe. Thanks everyone for all your advice with some luck and even more hard work I will be at preston on the 29th! cheers

Anyone know how much it would cost to get a modified blowtorch type O2 bottle certified to use as a 10 bar buffer?

-- Kev

Our coke bottle testing concluded that if pumping air (as opposed to CO2) there was no bang, the plastic heated and expanded until it quite quietly and undramatically released its contents at around about 200psi. Quite an anti climax when youre wearing ear defenders and cowering in the adjoining room!

The only problem I would envisage would be how to find a use for a holey plastic bottle that had formed itself to the shape of the inside of your robot ;)

Tim

Got it!

been asking all my old rc plane mates about this, and Ive found my 300psi figure.

Apparently, the old cylindrical 3 litre coke bottles were ok to 300psi. This was not the case for the smaller bottles, infact, the sculped 1 litre version blew up at half this according to the bloke I was talking to.

So how does he know? he tested them a few years ago, whacked them on a standard test rib and noted them all down.
He currenly uses a 3 litre coke bottle at 300psi in his quad pulsejet powered Vulcan.

there we go, I knew Id heard 300 somewhere.
as for the rest, Id reccommend we look at the coke bottle issue, with possibly more tests, as 50psi was there for rex, whats the difference with 70psi, or 80? if it saves money and is safe why no go for it?

I think coke bottles at 80psi should be alright.

Mr Stu

First 80 psi then 100 psi and then 150 psi then what?

Fizzy bottles were not designed for anything other than to contain fizzy drinks. Are we to type test every fizzy drink bottle on the shelves of Tescos? Their manufacturing properties will differ as will their burst pressure. Their burst pressure will vary with temperature (hot air from that little car tyre compressor), how do you monitor fatigue? If you crease the plastic by accident as a vented bottle is rather weak, should it be rejected? There are just too many variables with fizzy bottles for me to feel confortable using them at pressures above 50 psi.

Keep the fizzy bottles to the RRC bots, there are other more suitable alternatives for the bigger boys wanting higher pressure.

Paul
FRA Technical Team

Fair Enough - safest bet.

Mr Stu

Like I wrote. adhere to the FRA rules and be welcome on any venue.
Exceptions not included.

Or this might happen:

http://movies.flabber.nl/alcohol.and.chlorine.mix/http://movies.flabber.nl/alcohol.and.chlorine.mix/

Babeth called this autodarwination i believe.

Looks like fun.

Can I suggest every 1 who is considering testing a coke bottle to its max potential to be safe and wear correct protective gear and stand well back. And if possible don€™t be in the same room as the bottle going to pressure and insure you have the bottle wrapped in something to contain debris. If you think what you€™re doing isn€™t safe, dont do it!

Regards
Dave moulds
Team Turbine/PLF

Most importantly Never listen to what i say:)