Can you heat a co2 ram ?

Hi everyone,Happy New Year!
My robot wedgie had a problem of freezing up after two or three flips,and i thought it a good idea to fit a heater on to the ram cylinder to defrost the piston,it works well increasing the amount of flips to around 20.
I realised at the last event,after proudly anouncing my invention that it was against fra rules.
If it is i am sorry for my mistake and will remove the heater.It seems the rule was intended to prevent the heating of co2 bottles,and i cant see any danger in heating the ram.I have noticed a few larger robots heat parts of there machines before a fight,so i guess this will effect them as well.
Any advice would help.
thanks Andy.M

8.14. Pneumatic systems using heaters or pressure boosters are not permitted.

More heatsinks are an option, radiator fins are the only allowed , and passive means to get energy in the system to combat freezing.

And I do understand the possible mistake. I myself, even if I never used the heating methode, should have known better.
But Mentorn didnt allow bottleheaters.And the rest of the system had a handy arena heater with the flamepit.
This gave some of the seniors the wrong idea in the rules.

Fysicaly, there is no problem with heating the system. This should be protected by the 1000psi PRD.
Except the bottle, and even if the bottle is overheated the burst disk would prefent worse things.

As with all things concerning CO2, we full pressure users have to keep track of a few more,and much more restricting rules than any other robot builder. Spinners are the next runner uppers in this, and these machines are more restricted by the enviroment than by the rules themselfs.
Even if the old Mentorn Rules covered 99% of the potential problems with pneumatics.

The best method I have come across so far is to restrict gas flow into the buffer. This allows the CO2 to boil off in the gas cylinder without pulling liquid through into the rest of the system causing freezing.

I wouldnt worry about the mistake. Everyone is always pushing the rules to their limit and attempting to exploit loopholes etc. If we didnt then there wouldnt be any development of the machines.

Andrew ...Id suggest that your icing problem is caused by liquid co2 entering your system.... resolve this and you should have no need of a heater and also have more flips.

Woody, Andys system is not drawing liquid into the buffertank. There is a restrictor in the connection between bottle and collector.

The icing is normal for every high flow system, even with the bottle restricted.
The only way to enhance the system inside the rules is to add more heat exchange area and/or mass to draw heat from.

Id agree with Woody, once the system chills down from the HP gas Id guess that liquid CO2 will pass more easilly hence it freezes up. The only way we found to get around it was put less gas in the bottle to give more vapour space - although we never ran with a buffer. Maybe a bigger buffer will help, or cut the flow rate to the rams back a bit?

i second kane..

In Turbulence mk1, we used to have high flow pipes going into the buffers from the regulator. The ram used to be icey at the end of a fight. But it never leaked co2 (until the reg blew) Replace what pipe you have there with some small stuff (6mm od pipe) and it should help keep everything abit warmer. including your buffer tanks. When you draw gas quickly, things WILL get cold, no matter what. The slower the flow, the warmer things will stay. The only part of your system that should be high flow is inbetween the buffer, the valve, and the ram.

Id also suggest expanding any CO2 THROUGH the buffer ... end to end ....rather than simply adding a T piece .... thus any unwanted liquid expands in the buffer rather than being added to the flow from the buffer and on into the ram.

The internal bore of the main bottle valves ....that I have measured ... are fairly small and certainly in the case of a paintball tank tiny enough to constitute a restriction.

Paintball valves around 1/32
handwheel valves around 1/8 or 3mm ( feather size )

The system Andy is running doesnt have any small bore pipes in it. The connection between the bottle, valve and buffertank is a solid ali bullet, finned for more heat exchange surface.
The smallest bore after the flow restrictor/liquid stopper is 13mm.

The flow restrictor between bottle and collector stops any liquid CO2 entering the system.

The flow is the reason for the chilling, and restrict that flow you degenerate that system from powerfull into mediocre.

Quotes from my CO2 page.

With a gas fed source as the pressure drops in an orifice, liquid droplets nucleate and the percentage of liquid increases. At the interface between the liquid-gas and gas-solid regions (near 80 psi.), all the liquid converts to solid - yielding about 6 % dry ice.
With a liquid fed source as the pressure drops in the orifice, gas bubbles form and the percentage of gas increases until the gas-solid boundary is met. Here, the remaining liquid is transformed into solid - yielding about 45% dry ice.

So.......If you use compressed co2 in liquid form and utilise the gas that boils off from it ...then your containing vessel , bottle or cylinder will get cold .....if you exceed the ability of the bottle or cylinder to warm back up by absorbing heat from its surroundings then the pressure will drop and the contents may freeze.


I attempt to keep a majority of heat transfer freezing in the main tank and buffer and away from the ram using a combination of a main tank inverted dip tube a restricted or slow buffer refill of say around 2 seconds ... and a thru buffer tank feed.

Cant resist ....:)

The flow is the reason for the chilling, and restrict that flow you degenerate that system from powerfull into mediocre or none if the ram seizes.

Just out of interest what is the bore of the ram?

61mm bore 80mm stroke. Full ali construction, with HDPE piston and 5mm Viton Oring.

Assuming 45 BarA, around 7°C and no pressure drops (guess-timate figures), Id guess youre looking at filling the ram (under no load) in around 0.04 seconds through a 13mm orifice - which is pretty quick :)

The only thing I can think of is what Woody says, if the pipework gets bigger downstream you might be over expanding your gas and giving it too much opportunity to form ice. If possible Id be inclined to try it with all the bores at 13mm. It might help keep the pressure and temperature up a bit.

You can download an Excell spreadsheet that will give MY guesstimate of required MAX flow for a given mass , pressure ,leverage ratio and ram size.

Here

http://www.teamonslaught.fsnet.co.uk/Max.xlshttp://www.teamonslaught.fsnet.co.uk/Max.xls

or theres an embedded one in my first pneumatic page...scroll to the bottom.

http://www.teamonslaught.fsnet.co.uk/pneumatics.htmhttp://www.teamonslaught.fsnet.co.uk/pneumatics.htm

(Message edited by woody on January 03, 2008)

Andrew, first of all, very clever thinking with the heating of the ram. Indeed it is not allowed so we cant use a system like that but I like it when people think out of the box.

The plumbing on H2/Wedgie has already wide bores all the way through, nothing smaller than 13mm. If you need to get more heat into that system you would have to think about adding more heatsinks. Having the buffertank not in a T configuration but a connection at each end like Woody suggested will also help, but that would require a very drastic rebuild of the system. But I am sure it would be more efficient.

Would you be allowed to route your pipework around motors? (like a cooling jacket)
What about routing your wiring against the pnuematic system and using slightly smaller wiring than you would normally?

What are the safety issues with bottle heaters?

Most robots are effectively heaters since the entire electrical and mechancal system warms up during use. In that situation it seams a little odd to have a rule not allowing any heaters without clarifying what constitutes a heater. If it is a safety hazard then shouldnt it be defined? If it isnt, whats the rule there for?

How much could it improve perfomance in reality?

You can over define what is and what isnt allowed. I think its another occasion where common sense comes in.

In the end the event organisers are the ones that say yes or no to a bot running in their arena. If they feel that someone is doing something unsafe then they are the ones that say no.

I dont see a problem with keeping the system @ a working temperature .... as opposed to enhancing the system by heating.

Safe commercial methods exist for NOS cylinders.


http://www.turbobits.co.uk/acatalog/dynotune_105_2lb_nitrous_oxide_bottle_warmer_kit.h tmlhttp://www.turbobits.co.uk/acatalog/..._bottle_warmer _kit.html

I doubt those pressure switches would handle the vibration in a robot.

No one has said its not aloud yet! The rule was put there to prevent the dangerous practice of heating bottles,not to defrost a ram or am i wrong.
I honestly thought i had a good safe and cheep idea,which should be considered and not dismissed just because its not somthing you cant do on a lathe.
I like the idea of connecting the bottle to the buffer tank,if it woks!I have a system that works without spending a fortune and enyone can do it. As far as i can see the advantage goes to the man with a lathe or frendly workshop as i have neither i have to invent ways of competing which are within my means and within the rules.
Who has the final say on this?
I hope its a man who has no engineering skills.

At the end of the day the system designed by mario is the best fliper out there,i can understand the competition being scared of it:uhoh:

Im not scared. :)

Rule 8.14 covers the whole pnumatic system, not just the bottle. Therefore heaters even on the ram is not allowed.

(Message edited by leorcc on January 03, 2008)

As it currently stands this system would not be allowed to run at any of our events, as it breaks a major rule, whether its safe or not doesnt come into it. If one robot is allowed then all robots have to be allowed to use the system (im sure many would have already tried the idea had it been allowed).

andrew we will after have a flipper match next event all flippers in 1 fight

ok no heater,do you think this rule will ever be changed.
I will take off the radio switch/relay,is it ok to defrost the ram between fights on the bench??

Hi Kenny,question is are you better than an 11 year old?:) We were going to leicester start of feb,i have registerd but there is a note on the signe up page saying that they are no longer accepting featherweights,so im on the reserve list.So your flying lesson may have to wait!

im going to the leicester event so i will look forward to the flying lessons but beware once i get ya, you will be out :)

Andrew, Due to two feathers pulling out of the event there will be a place for you. I will update the list tonight.

Dave
http://www.robotslive.co.ukwww.robotslive.co.uk

wahahahaa!! bring it on now :)

quote:

ok no heater,do you think this rule will ever be changed.

I doubt it. Unless there is a proposal from FRA members to change this rule, put forward to the FRA reps, and voted on in a FRA meeting.

quote:

I will take off the radio switch/relay,is it ok to defrost the ram between fights on the bench??

I think that is up to the Event Organisers wether they allow it or not, but I dont really see a problem in it. I assume you are not heating it to absurd temperatures I hope? The Plastic inside the ram can melt you know.

Better get welding then! I seem to have a few split welds after meeting little spinner:crazy:at the last event oh and trying to activate the flipper in the last fight with the safty bar in.
And no Mario,it doesnt do toast.
Are there any rules about injecting de-icer in to the bottom of the cylinder on the up stroke of the ram?i recon i can make it work.

Well I tried to flip the Robotslive arena with H3 that didnt work so well either.

You know we did have some icing in H2, but never that much that it got a real problem. We did XFM without much icing problems at all, apart from the bottle itself of course.

Have you checked that your liquid stopper is still in place? Its between the bottle and the buffertank, straight behind the part where you screw the bottle in.

I believe that Leo is refering to something like this.
http://www.univer.com.au/breather-vents-2941.htmhttp://www.univer.com.au/breather-vents-2941.htm

I can check,i haven,t messed with any part of the system other than the heater.I will look an report back!

We used to inject a few ccs of car radiator anti-freeze (the thick blue stuff) into our gas system before a fight with Mute. Not sure if helped that much but it seemed to keep the rams lubed up for the first flip or two. Always worth a try but make sure its none flamable in case it goes pop under compression or something.

Hi Daniel,
I was thinking more of injecting in to the bottom of the cylinder under the piston im gessing thats where the ice is.I think there is a hole in the bottom of the ram to let the expanded gas out.A radio switch or micro switch connected to the flipper arm could triger a measured amount of something to ease the return of the piston.
I think Mario said the piston is hdpe with an o ring,so i would want to do a test on another o ring to make sure it does not damage it.Maybe all i need is a little lubricant? im not sure if aluminium and o rings need maintenance.... Mario?

I wouldnt recommend putting antifreeze in the system.

1. Its toxic and would leave a toxic vapour in the arena.
2. It doesnt work down to the temperatures CO2 gets to and it will freeze.

The neat anti-freeze we used was good for -35°C, although we used it in very small quantities - about 0.5 litres in 3 years. Didnt seem like a bad idea back when we did it but thinking about it now, yes it is toxic.

http://en.wikipedia.org/wiki/Carbon_dioxideCO2