Pneumatic questions, sorry!

[Max]

I am just starting to think about my next robot and like the idea of a featherweight pneumatic flipper. I have read through a lot of the old threads but am still left with some questions. I still don't understand what the stroke and the bore mean? Also I remember seeing a link to a great website on pneumatics in combat robotics but I can't find the link, does anyone know what it was? I was also wondering if you realy need a buffer tank because due to my design i can only fit in either 1 main tank and 1 buffertank or 2 main tanks which i think i will need to get plenty of flips(i am thinking of
Using p16oz paint ball gun bottles) I am sure that more questions will follow soon but thanks for now.

[Eventorizon]

Hi All

We are going to be taking out first steps towards building some pneumatic machines. We got hold of 2 cylinders of Jamie a while back an I have 2 machines in mind. As we only have spinners, these machines will be for the Robotwars and other events that don't have a Class 1 Arena.

1: A 2WD flipper using a small 10 Bar, 40mm Bore, 75mm Stroke cylinder. This gives approx. 300kg of force at the tip of the cylinder which will be dropped to about 30kg over the flipper arm.

2: A 4WD (2 motors, belt driven) Horizontal spike machine with a 16 Bar, 50mm Bore, 100mm stroke. This will give around 500kg of force on the end of the piston which will have a hardened spike on the tip.
We know that spike bots have not been overly successful over the years but we want to make something different, but given some of the thin armour out there on some machines (LF3, LH3 Explosion) it might be able to do some damage.

The first issue we have is what Tanks to use. We got what looked like a 16oz paintball tank and we also picked up an empty 1kg powder fire-extinguisher which we were thinking of using as buffer tank in the Flipper.

What standard tanks do people use and what valves as well. We have, what I think is, a 3-2 valve to direct the flow in double-acting cylinders.

I just want thoughts on the 2 ideas. I am going to be putting up concepts fairly soon but I cant really do it until I know what parts are going inside. We might have some fun making an Asymmetric machine but neither machine is meant to be overly competitive, just low cost and fun.

[Liftoff]

My preferred solution is a 5/2 way valve operated system with QEV, buffer tank and spring/bungee return. I use all paintball parts for the reason that they are readily available, not expensive and properly rated. Buffer tank and main tank I'd use 12oz tanks, paintball low press regs are available as well, and they connect directly to the tank so there's no hassling with adaptors. 16bar is a bit on the high side to find LP valves and push fittings rated at that pressure.
The thing you should really take care of is making sure there are no restrictions from the buffer to the ram, that will be the difference between a flipper and a lifter!

[typhoon_driver]

the thin armour on LF3 is titanium sheet. You will struggle to do any kind of damage against that kind of armour with a spike.

By all means build one, but just be aware that you will likely do sod all damage.

[psychostorm]

Maybe if you rammed it with a run up...

[Eventorizon]

What pressure are the push fittings usually rated to? The plan was to make the spike bot from MDF. We are not massively fussed about weight as its never going to be for competition. As it will all be fixed I was going to get parts you have to bolt together rather than push fit parts.

Also, thanks to Kane's talk at the Robochallenge awards we know his list of little tricks to get the most out of a pneumatic system, like making sure the flow its straight just to name one.

And I know what the armour is Gary. 1.5mm Grade 6 on the sides and back with 3mm Grade 5 on the front. I still think 250kg of force is enough to do something to it. (250kg as we will push ourselves back as we fire, halving the force)

[plargen]

250kg of force will just push the 2 bots away from each other and if your lucky make a small dent

the main issue is that they way so little and don't have a great amount of grip on the floor

[typhoon_driver]

No need to have the sarcastic response. Only trying to save you some time going down a route that won't work.

[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.