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#1
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Basic pneumatics questions
Hello there,
I'm from team 1257. After having played defense (and not much else) in the past district event, we are looking to attempt to implement a solution for launching the ball over the truss for the next competition, in roughly a week and a half. While I fully believe in my team's ability to do so, I do have a couple questions about pneumatics. 1) At competition, I was talking to teams and they said they had both a high pressure and a low pressure circuit going, at 120 and 60 psi respectively. How is this possible, if there is a pressure regulator at 60 psi that's required before all pistons? Furthermore, how can the tanks get up to 120 psi if there is a 60 psi regulator in the circuit? The way it appears in the FIRST setup (http://frc-manual.usfirst.org/upload...Figure4-15.jpg) it doesn't look like there's a break between the tanks and the regulator ... 2) Is there a limit to the number of tanks that we are allowed to have? Also, are we allowed to place tanks after the regulator? I haven't found anything specifically mentioning either in the rules. 3)For a team new to pneumatics, and given the time constraints, I think a latch system to store energy, or any tampering with the pistons (removing fittings to make flow faster, etc), is out of the question. Furthermore, since a 2-3 stage setup would be needed to make a successful ram, would our only option become a trebuchet? 4) I found tanks from our old seasons which are only open on one end (threaded opening). All other tanks (metal or plastic) have threaded/push to connect openings on both sides. Are the one sided containers tanks, and, if they are, would they just be connected to other tanks at the one end, using a t-connector? We have about 30 pounds free to work with on the robot right now. Would this be enough for a full pneumatic system? If I'm not mistaken, we would be looking at something like 2x 10" stroke 1" bore cylinders (I think that's how one specifies cylinders?), along with the older, more heavy-duty compressor, a few tanks, likely metal (we have new black plastic Clippard tanks but are hesitant to use them due to stories of the white ones fracturing), and a little bit of tubing, brass connectors, and a few electronics. I can't imagine this getting up beyond 30 pounds; that being said, is there anything blatantly obvious I'm forgetting? That being said, I would appreciate if someone could either answer these questions (and anything else that you think a beginner to pneumatics should know). I would also appreciate any general tips/pointers, or really anything else. Thank you for your time and for reading, Hades Edit: Slightly unrelated. Is there any use for rotational cylinders? I found one sitting in our stock of pneumatic components and I was wondering if it would be remotely useful for FIRST related things. If we're allowed to use it, I see it as possibly being useful for blocking the pistons to build up pressure, among other things. Do teams use them at all? Last edited by TheHolyHades1 : 19-03-2014 at 01:28. |
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#2
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Re: Basic pneumatics questions
1) There is a direction associated with the regulator, If you look closely at one there's a arrow. Everything below that will be the regulated pressure. Everything before the first regulator is referred to as the high side.
2)No Limit except for space and cost considerations. Yes you can put tanks after the regulator but usually not done. 3) You can use a latch system to store the energy. I think what will work for you will depend on more information. 4) you can use various fittings from brass Ts to plastic quick disconnect T's. You may screw in quick disconnect fittings into them. 30 Pounds should be sufficient for a pneumatic system. The old compressor weights in around 10 lbs. You can use the rotational cylinder. |
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#3
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Re: Basic pneumatics questions
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A couple of other tips: Set up a test system first, to validate that your knowledge of pneumatics works. Leak check with soapy water, sprayed onto the tubing near the valves at the suspected leak point. Go with an onboard compressor--I suspect you'll have lots of leaks; you want to be able to counter them. Cut your tubing at 90 degree angles; that'll help with reducing leaks at fittings. |
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#4
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Re: Basic pneumatics questions
But you may hook up multiple solenoids to 1 spike relay. You can also hook up 2 individual single action solenoids to 1 relay and still maintain control over both individually.
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#5
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Re: Basic pneumatics questions
You should be able to fit a pneumatic system in 30lbs withholding allowance fairly easily, especially considering almost all of it will be COTS parts. You'll have to do a of plumbing and testing the system on Thursday (especially considering it doesn't sound like you've done one before), but this is a time issue instead of weight. Read through all the official materials on pneumatics from FIRST so you can make sure to build a legal system, make a solid plan (if you can, CAD out the location of tanks/solenoids/compressor), and then ask around for someone really experienced with pneumatics as soon as you get to competition. You'll need their help putting things together the first time around, especially finding and fixing leaks.
I would use the black Clippard tanks any day over the metal ones, especially considering weight is a concern. The problems (which frankly, in my opinion have been dwelt on a bit too long) were with the white tanks, and unless you physically damage the black tanks, you won't have them explode on you. The metal tanks weigh a ton, and only store a tiny bit of air compared to the plastic ones. The teams talking about two pressure levels were likely only referring to the stored (in the tanks/off the compressor) pressure and working pressure (in the cylenders/solenoids/off the regulator). If they weren't, they had an illegal system. There's no restriction on whether you have tanks above or bellow the 120 psi level. You can keep them on the 60 psi side if you want. There's no limit on number of tanks, except the rules for the robot size and weight (you can't have an infinite number of tanks, as they will be too big/heavy). Figuring out how to build a pneumatic catapult (which sounds like the way to go, from what I've heard on CD) is something that needs either prototyping or for you to copy someone else's design. It takes a fair amount of iteration to get a system that will throw the ball exactly how you want it, and I certainly wouldn't build your final mechanism without doing a bit of prototyping and research first. I hope someone who actually built a pneumatic catapult will chime in on this thread. |
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#6
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Re: Basic pneumatics questions
Thank you both. How would you recommend that we cut the tubing? I've tried to use scissors and xacto knives/box cutters but none of them seem to be doing the job well, or at all in some cases. Should I be using something like wire cutters?
I should mention that there is already a hinged ramp on our robot which we are simply planning on actuating with 2 cylinders at this point. As was mentioned, we should hopefully be able to attach near the bottom of the ramp (close to the hinge) to help it swing forward rapidly. |
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#7
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Re: Basic pneumatics questions
Last edited by kevin.li.rit : 19-03-2014 at 01:52. |
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#8
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Re: Basic pneumatics questions
Diagonal cutters should work--but as I noted earlier, you want that tubing cut as close to straight across as you can get. I've seen special cutters for the stuff that help with that, but I'm not sure where to get 'em, especially on short notice.
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#9
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Re: Basic pneumatics questions
I like to use wire cutters. Just make sure to squeeze hard, so the tubing it cut nice and clean. If the cuts aren't perfectly straight, your system will leak.
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#10
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Re: Basic pneumatics questions
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There was also talk of using some interesting pneumatics physics where, between 3 pistons, they were able to achieve (if I remember correctly) 250% of the normal psi? Is this even possible, or am I simply remembering wrong? Quote:
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#11
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Re: Basic pneumatics questions
Gotcha, thanks. As the poster above pointed out, apparently McMaster carries a tool for this. They have a warehouse near us, perhaps we can go tomorrow and pick one up directly. Thanks again.
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#12
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Re: Basic pneumatics questions
I've also heard that L-connectors should be avoided whenever possible; is this true, and are there any other connectors that I should be avoiding?
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#13
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Re: Basic pneumatics questions
I wonder if the cutters at the center of most needlenose pliers will work?
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#14
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Re: Basic pneumatics questions
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It's illegal (and unwise) to configure pistons such that they will boost the PSI in another one (although it's possible). If they were doing it like this, they weren't following the rules, and have a potentially pretty unsafe situation on their hands. What they were probably talking about is configuring the pistons such that they generate three times the force, maybe just by moving where they attach to the catapult, or by just using three side by side instead of one. It's just basic physics/mechanical advantage stuff. They also could be talking about getting a 250% faster flow rate by doing a pneumatic tank on the vent, using special solenoids, or some other tricky pneumatics stuff. |
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#15
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Re: Basic pneumatics questions
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