Pneumatic questions, sorry!

[Liftoff]

Normally push fittings are rated at 8 to 10 bar, I had one blow apart at 11bar. There are all metal ones good for 15bar, but they are expensive, the way round that is using small 1/8 fittings on all the system apart from the buffer and the ram, the smaller fittings cost less..... btw. it will be difficult to do away with push fittings, even if everything is fixed, as long as you're not using metal tubing and compression fittings!
Alex, there's no way you'll be able to penetrate titanium alloy, neither at 1.5mm and much less at 3mm, at most maybe you'll dent it, that's all. But you're free to prove us all wrong!

[Max]

Not sure if I agree on the forces generated by your rams, I think 40mm bore gives you 120kg of force and the 50mm bore gives you 300kg?
I am making a hw spike bot which I hope should be fun, I am going full pressure because I think the key to it is making it fast, so I would definatly use a big QEV to feed it and a big buffer. You'll have to use the MDF well to hold the required forces.
I would use paintball on/off valves as they are lightweight. If you can avoid using paintball tanks as buffers I would as they are much heavier than necessary.

[Eventorizon]

I am not expecting to punch through Titanium. I just want to do something different. And if it doesn't work then I can build a normal flipper.

To calc the pressure I am using a converter to go from 16 Bar to 1.6 N/mm^2. From that its (25 x Pi) Squared... oh darn it... I hate using the calculator on my PC. Right... (25 x 25) x Pi = 1963.49 mm2, which gives a total of 320.4kg on a point at 16 Bar.

And the yield strength of Ti 5 is 950MPa. Ok, that is a little impossible. Oh the up side HDPE's is only about 30MPa so Explosion is in trouble.

Does anyone know what cylinder Heatwave used? It looks very similar to the one we have.

2013-05-26 20.59.40.jpg
Also, can someone give me the dimensions of a 20oz Paintball CO2 tank.

[Max]

Earlier in this thread mario said the 20oz bottles are 330mm long, 75mm diameter bit I haven't personally checked that.

[Liftoff]

Just checked mine, its 240 mm long (without the valve) and 64mm diameter, weighs 463gr...don't know what other tanks you could use which weigh significantly less.
Regarding the ram, I have a similar one to it on my robot, but had to modify it. The problem with those rams is that although the threaded ports might be 1/4" or even 3/8", the orifice inside will be much smaller!...that's one of the reasons restricting flow I mentioned on my earlier post.

Edit: Opps my tanks are 12oz sorry!

Edit 2: 20oz tank measurements - 80mm dia, 270mm long, weighs 830gr (incl valve)

[Eventorizon]

I was going to say, 20oz are much bigger. 12oz should be enough. I have also figured out how to use the gas used to fire the cylinder to reset it without any extra gas.

The 50mm bore one has open ports with no restriction but the 40mm one has maybe 2mm dia holes a little way into the ports. Provided I am still at uni I can resize the holes to bigger ones if need be.

[RogueTwoRobots]

We have, what I think is, a 3-2 valve

If it's the one you got from me, it's a 5/2 valve. And there should be both a 12V and 24V coil to offer some flexibility in operating voltage.

A spike will indeed do minimal damage, but as long as you have fun with it, that's the important bit. My axe weapon will probably do the same, but in the short while I've used it so far, it's been fun
It's also interesting that whenever I mention Robot Wars or robot combat to someone who used to watch it back in the day or knows roughly what it is, the most common response is 'Do you know what would've been a really good weapon? A big spike' or 'Some sort of EMF weapon'. I'm quite well-versed in explaining the ineffectiveness of spikes and the illegality of EMFs nowadays.

[Liftoff]

I was going to say, 20oz are much bigger. 12oz should be enough. I have also figured out how to use the gas used to fire the cylinder to reset it without any extra gas.

Yep, no need for 20 oz tank, I use 12 oz tanks both for main and buffer with a 63 x 73mm ram, and it works well... but tbh, the there's not much of a difference in size between the 12 and 20 oz tanks.

[Shakey]

Don't be fooled by the comparatively low strength of HDPE. You are looking at the solid force being put out but you need to look at impulse instead which takes into account the time the force is applied over. Ridgid metals do not deform on impact so maintain a high impulse from that force. HDPE is great at having a bit of flex and deformity, in other words it stretches out the time the impact lasts for for far longer than metal so effectively it experiences a lower force than metal does. It is what makes it such a good armour against spinning weapons because though it may have a gouge taken out it pretty much took a good amount of force out the robot. The same amount of energy is still transferred but it is the difference between putting 1kg on your robot for 1000 hours or 1000kg for 1 hour.

Also the 320kg of force is only true if you can get the flowrate high enough to keep the pressure in the cylinder up as it expands, otherwise the high pressure will only be achieved fully once the ram has finished actuating.

Now I'm not sitting here to say not to build it, just to inform you more. I myself am building an axe robot that I know is never going to properly break other robots but just hitting stuff is going to be fun! I would love to see you prove us wrong too (until my feather is impaled :P ), just have fun with your design and it'll be good!

[Max]

Hi,
What kind of springs do people use to stop their QEVs misfiring when the gas is dumped? Where can you get them from?
As I see it, it has to be a very weak spring which compresses down to virtually nothing.

Also is there a reason my 5/2 solenoid valve seems to get stuck in the on position when I have the bottle turned off before a flip, I then have to put my thumb over the port where the gas come out for a while until it flicks over to the off position.

[Liftoff]

If you connect the dump valve to the buffer tank, then you should get no issues with the QEV firing when you dump the air. To dump the air from the QEV to the valve fire the weapon, it will not move provided the main supply is closed and the dump valve open. Don't know what other solutions there might be.

[geeza]

I've never had it fire, the pressure should drop evenly both sides of the qev.

[Max]

It would be very difficult for me to put the dump valve between the buffer and the QEV but if that is my only option I will probably have to make a custom component to make it fit together in the space I've got.
I don't know why yours doesn't fire, as I see it, it is the same as switching the 5/2 valve to dump the gas in the pipe going to the QEV causing it to fire.
perhaps an option would be to severely restrict the gas flow out of the dump valve to the pressure doesn't drop fast enough to fire it, but then it would take forever to empty. I am sure Mario said to me at Maidstone I could use a small spring to stop it misfiring but I am struggling to find one suitable. The best I have come up with is using a paper clip wrapped round a large pencil to make it into a spring shape but I doubt that will work for long!

[Liftoff]

Can't you fit a Tee fitting directly to the buffer? Then you could connect the QEV to one side and the dump valve to the other. Don't know how placing a spring on the QEV will work, the way I see it once you dump the inlet of the QEV, spring loaded or not, the pressure inside the buffer tank will push the sliding seal inside the QEV and fire the ram.

[Eventorizon]

Been watching back over RW and trying to spot all the little hints and tips teams give to maximise the power or efficiency of their set ups.
The one that stood out was using Liquid CO2 like in Chaos 2 and a few other machines but so far as I know we cant get liquid CO2 at events. Also it seems logical that you would end up freezing the valves as the gas expanded into the cylinder causing it to jam. But there must be ways round this if Chaos 2 can use it with no problems.

Another which Kane mentioned was to have the largest buffer tank you can, so the gas can easily flow into the cylinder. Also making the routes as direct and straight as possible so you don't waste energy in the process.

Are there any other little tips people can suggest, or correct me on these ones.

I also have this half used powder extinguisher in my flat.
2013-06-03 15.22.00.jpg
Physically it is fine its just never been repressurised. Would this be alright to use as a buffer or even a main tank?

It has the following on the side...
Working Pressure: 13.5 Bar
Test Pressure: 22 Bar

The maximum our cylinders can take is 16 bar so it would be 37.5% less than the testing pressure. And if I remember right, parts must be tested to 20% more than their intended operating pressure so this would be ok.