Hello. I was wondering if it is posible or rather legal to conect 2 pnematic cylenders in series, like you would a battery. This would mean connecting them on the opposite sides. There would then be a line from each cylinder going to the solenoid.
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Legality changes year to year.
It’s possible. But what purpose would it serve?
I’m currently working on a system that allows a omni wheel to pivot down, and to ecmven out some force this is the solution I came up with
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Can you post a diagram (MS paint will do) of the setup you’re asking about? For some reason I can’t picture it.
In general, FRC doesn’t really care what you do with cylinders and air lines and solenoids as long as no pressure higher than 60 psi gets to your actuators. For example, I’m fairly sure that a servo attached to a dump valve to make an adjustable pressure regulator was once ruled legal. Rules change though, and there are some neat caveats to that rule of thumb.
If I understand this correctly, isn’t it more like cylinders in parallel more than cylinder in series? After all, air goes from solenoid to atmosphere through either cylinder, not both one after another., which wouldn’t’t make sense.
If so, then it’s probably gonna be legal, and simply act like a one big cylinder with a larger bore.
Seconded. A diagram would be helpful here.
Here is a rough dwawinghttps://uploads.tapatalk-cdn.com/20171117/d4c3907bbc4921d82a1fb93bc3c7b22f.jpg
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Is the goal for these cylinders to fire at the same time? If so I’m not sure this accomplishes anything that a standard parallel setup doesn’t.
The right half of the upper cylinder and the left half of the lower cylinder will have no pressure. Actuating one might move the other because volume changes, but any force can compress the cylinder since there isn’t pressure.
Yes that is the goal. What does the standard set up consist of
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Set them up in parallel; use a T or Y coupler to attach each side of the solenoid to both cylinders.
Yeah, that’s not going to work. Basically, that’s going to use the relatively low pressure exhaust from the first cylinder to fire the second one, and it is likely that the second cylinder will not reach the full stroke. Instead, if you want them to fire simultaneously, wire them normally, but use a splitter off of the solenoid outputs.
I see what you mean. Only one would have any actual force
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They would both have equal pressure and force in that setup.
Consider the link between the top cylinder and the bottom cylinder. It contains a fixed volume of air, with no access to a pressure release valve or regulator.
In the event the top piston was compressed and the bottom piston extended by external forces (whatever is attached to the pistons) then the pressure in the line could exceed 60PSI. I believe this could be a problem with passing FRC tech inspection.
I can’t quote a rule for the upcoming year, of course, and I’m not about to go rummaging through old Q&A’s to find the definitive answer, but I seem to recall seeing a Q&A about using sealed pneumatic pistons as shock absorbers in a suspension system. The Q&A… if my memory serves me… said it was not allowed because there was the possibility of the pressure exceeding 60PSI based on the external forces.
You might also want to consider what the impact of the piston rod in the system will be. The right hand side of the top cylinder will have more surface area than the left hand side of the bottom cylinder that it is attached to. This means that the bottom cylinder will move a greater distance than the top cylinder.
I’m not sure what you’re trying to achieve here, but if it’s getting twice as much work done with the same volume of air at the same pressure, you’re trying to cheat the conservation of energy.
It does remind me that on our 2013 robot we mounted cylinders to each other, pointing in opposite directions:
__________
==|__________|
|__________|==
This put the cylinders “mechanically in series” such that the cylinder pair was able to extend to roughly 2.5x the collapsed length. However, they were plumbed in parallel.
Your first paragraph nailed the problem. It’s a violation of R94 to run it this way, at least for 2017. No Q&A digging required.
R94. Any pressure vent plug must be:
A. connected to the pneumatic circuit such that, when manually operated, it will vent to the atmosphere to** relieve all stored pressure** in a reasonable amount of time, and
B. placed on the ROBOT so that it is visible and easily accessible.
If the compressor is not used on the ROBOT, then an additional pressure vent plug must be connected to the high-pressure portion of the pneumatic circuit off-board the ROBOT with the compressor (see R85).
There is no way for the main vent plug to release any stored pressure from that middle section. Therefore, at a minimum you’d need to put a second vent plug, make it accessible, and make sure it’s opened/closed properly. But that would likely introduce a long loop of tubing, which will tend to act as a delay on your second cylinder. Essentially, you can’t do it cleanly and safely. (You might be able to get away with a regulator instead. But still… you need to be able to vent that air, and yes there is air in there!)
Go with Chak’s post; that’s the standard method.
My assumption that this is for a FIRST application and that the cylinders are the same volume.
Lets call the top cylinder A and the bottom cylinder B
When you start adding pressure to the bottom of cylinder B the rod will start to move, causing pressure in the top of cylinder B to build, which will transfer to the bottom of cylinder A, causing the rod of cylinder A to extend.
Once cylinder B is fully extended the force will be (approx.) 60*bore area.
Cylinder A will be (mostly) fully extended (minus frictional forces) as well but The force on Cylinder A will be 0 since the volume of air that was transferred to cylinder A is the same as was in cylinder B (and thus no compression).
Jason,
There is little issue with going over 60PSI as any force on cylinder A that compresses the air will force cylinder B to retract once 60PSI is hit in the trapped volume. Once 60 PSI is reached the pressure on the top of cylinder B will become greater than the pressure in the bottom of cylinder B and cause it to retract.
All of this is moot though because Eric is correct that trapped volumes are not allowed (barring a rule change that I do not expect).
This neglects the external forces on the rods at the ends of the cylinders. If you push the top one in and pull the bottom one out, you can generate as much pressure as you like - until you break something.
Correct.
I was addressing the issue as drawn.
Should you push (to retract) cylinder A and hold Cylinder B (in extended position) you can create very high pressures in the trapped volume.