Basic pneumatics questions

[TheHolyHades1]

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?

[kevin.li.rit]

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.

[EricH]

Originally Posted by TheHolyHades1

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 ...

The high pressure is storage, regulated down to 60 psi for working pressure. Often it's easier to refer to the two sided separately. Tanks can be on the high-pressure side; cylinders cannot.

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.

No, and yes. I believe both were asked in Q&A. I will comment that the more tanks you have, the more time your one compressor will take to fill them. If you can't refill after a match in 5 minutes or less, you'll be at a disadvantage in eliminations.

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?

I think you may want to consider the application of leverage. If you have the piston fairly low on a linkage, near the pivot, and the piston fires quickly, imagine how fast the OTHER end of that link is going....

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?

Based on the description, yes (given no moving parts), and yes (though connector is up to you).

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?

I don't think you're forgetting much, as long as the "electronics" includes solenoid valves. You'll also want the Solenoid Module for the cRIO, or a Spike per solenoid valve. You've spec'd the cylinders correctly, near as I can tell. But 30 lbs with the older compressor and metal tanks could get a little bit tight, particularly with the material of the launcher itself to factor in. Also verify that you have all the stuff that is required: relief valve for the compressor, manual vent valve, gauges, the regulator, and the pressure sensor.


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.

[kevin.li.rit]

Originally Posted by EricH

You'll also want the Solenoid Module for the cRIO, or a Spike per solenoid valve.

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.

[TheHolyHades1]

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.

[kevin.li.rit]

A Pneumatic Tubing Cutter like this.

Edit: McmasterCarr Carries them too

[EricH]

Originally Posted by TheHolyHades1

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?

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.

[TheHolyHades1]

Originally Posted by EricH

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.

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.

[TheHolyHades1]

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?

[DampRobot]

Originally Posted by TheHolyHades1

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 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.

[TheHolyHades1]

Originally Posted by DampRobot

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.

I wonder if the cutters at the center of most needlenose pliers will work?

[Mr V]

Cylinders come with no fittings so leaving it out of the retract side to make the cylinder extend quicker isn't anything advanced. To retract the mechanism you may be able to use gravity alone, if that is not enough a light spring like a bit of surgical tubing can help it get started.

For solenoids the only restriction this year is that the maximum port size is 1/8" NPT. A single acting solenoid is all you need for a gravity/spring retract style set up.

It can be very effective both a pneumatic catapult and focusing on getting those 10 truss points. At the Mt Vernon district event team 4918 used a pneumatic powered catapult and and focused on getting the truss points on every cycle along with a triple assist to become the #1 seed.

Check out this thread for a render of their robot. http://www.chiefdelphi.com/forums/sh...ht=4918+render the only thing that isn't in there is a bit of surgical tubing to make sure that it gets back from the vertical position so that gravity can return it to the loading position.

[Answer42]

Bit of a deviation here. But is a pneumatic catapult really the best option here? Especially considering that you don't already have the system on the robot, it's just one more thing to add along with the catapult. You said you have 30 pounds left, and unless you've used all your cims, mini-cims, and banebots motors you still have plenty of power left. Electrically driven catapults are super simple, requiring you to just hook a gearbox to a shaft via some sort of pulley or chain. No locking mechanism, springs, or pneumatic required. They require complex coding to make accurate shots, but just trussing could be accomplished by something as simple as boom done's system from RI3D. Using a torque limiting belt removes the need for precise control. IMHO it would be the easiest way to add a trussing capability to your robot. But that's just my two cents.

[TheHolyHades1]

Originally Posted by Answer42

Bit of a deviation here. But is a pneumatic catapult really the best option here? Especially considering that you don't already have the system on the robot, it's just one more thing to add along with the catapult. You said you have 30 pounds left, and unless you've used all your cims, mini-cims, and banebots motors you still have plenty of power left. Electrically driven catapults are super simple, requiring you to just hook a gearbox to a shaft via some sort of pulley or chain. No locking mechanism, springs, or pneumatic required. They require complex coding to make accurate shots, but just trussing could be accomplished by something as simple as boom done's system from RI3D. Using a torque limiting belt removes the need for precise control. IMHO it would be the easiest way to add a trussing capability to your robot. But that's just my two cents.

Well, the reason behind using pneumatics (apart from coolness factor), is that I want to have myself and my team get some experience with the setup before I leave at the end of this year. That being said, I should mention that we've had some issues in the past with shooting things with motors; we want to try something different this year, which is why we're looking at pneumatics. And you're right, trussing doesn't require much precise aiming, which is exactly what we're going for at the moment.

[DampRobot]

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.