Flow control?
 

In our prototyping tests we could not get cylinders to extend quickly enough to provide enough force to launch the ball very far, but we've seen videos of teams launching well over the truss using a single cylinder. While we don't have the most experience with pneumatics, we believe this is due to the lack of an adequate air flow rate to the cylinder. If you've successfully launched a ball with cylinders, what did you do to get enough air flow?

Re: Flow control?
 

How high would you define as a successful launch with just a piston? We've had okay results in that we made on that can move the ball a decent amount but it doesn't have the range we want.

Re: Flow control?
 

I'd say a successful launch is from about 3 feet off the ground over the truss from a few feet away. The videos I've seen are clearly powerful shots that span a decent distance (I'd link to them but they're on facebook), but my goal is to just be able to lightly lob the ball over the truss reliably. Our tests maybe move the ball a few feet, but not enough for shot that would make it over the truss.

Re: Flow control?
 

I don't think you can use a flow control to step up the pressure to a cylinder. I've only ever used flow control valves to slow cylinders down. What cylinder are you using? What's the stroke length, diameter, and psi rating? You can use a higher psi and/or a smaller cylinder diameter to extend more quickly. If you have a regulator in place between your air tanks and solenoids you could tweak it until it's allowing a higher psi to flow to your cylinder (just make sure it can stand the higher pressure; some might not be rated to the full 120 psi we're allowed).

Re: Flow control?
 

In 2008, 1075 came up with a pneumatically driven firing mechanism that involved 3x1.5" bore cylinders, fed from independent valves (switched together in software), that pulled a block and tackle pulley system to move a carriage along a rail (and into a hard stop at the top).

While not as simple as "punch ball with pneumatic cylinder", strictly speaking, it WAS firing the trackball using pneumatic power. IIRC there was also elastic power coming from the surgical tubing to assist the pneumatic cylinders in the "firing" direction (which the cylinders would then stretch to reload for the next shot).

Re: Flow control?
 

The cylinders provide plenty of power to move the ball, but to get the speed you are looking for you might have to add springs or surgical tubing to your mechanism to get the ball over the truss.

Re: Flow control?
 

Wait, you can't have a cylinder at 120 PSI, can you? Doesn't the working side have to be 60 PSI?

Also, they eliminated rules about valve flow rate. The only remaining rule is that the limit is 1/8 inch NPT diameter. In my understanding, you can get a new solenoid valve that should make a cylinder extend faster. Thats my understanding anyway.

Re: Flow control?
 

There are a few things to try to get speed out of a cylinder.
#1 Get a solenoid with the highest CV you can find.
#2 Keep your tubing runs as short as possible (even go as far as plumbing the solenoid right to the cylinder.
#3 Remove the exhaust port on the cylinder and use spring return.
#4 Use low side storage tanks as close to the solenoid as possible.
#5 Replace a large diameter cylinder with several smaller diameter cylinders each with their own solenoid.
#6 use a lever to speed up the action, kind of like gearing up a motor.

Anything to get that air going as fast as possible into that cylinder.

Re: Flow control?
 

Oops, yup. You got me.

Re: Flow control?
 

To this end, if you wanted to be really extra nutty, get a solenoid with 1/8" NPT ports, with the highest CV you can find, plumb the output directly to the cylinder with brass fittings or pipe nipples (I think pipe nipples might count as fittings?). Also plump a large low side reservoir directly to the input of the solenoid. Yes it'd be big and bulky, but it'd also get you the fastest actuation possible.

Re: Flow control?
 

Indysam
Can you explain this to me.
#4 Use low side storage tanks as close to the solenoid as possible.
How does this work and what does it do?

Re: Flow control?
 

If you want pistons to extend or retract faster, remove a fitting from either your inlet or outlet on the cylinder. Essentially you will only hook one side of the cylinder with air, while the other side will have an open port with no fitting. Try it and let me know how it goes. We have had great success with it.

Re: Flow control?
 

that much I understood. What I dont understand is
#4 Use low side storage tanks as close to the solenoid as possible.

Can you explain that?

Re: Flow control?
 

The regulator and hose in proportion to its length create restrictions. So if you've got a low pressure storage tank then you eliminate the regulator's restrictions and if you place it close to the valve as possible and the valve as close as possible to the cylinder you minimize the restriction caused by the hose.

Re: Flow control?
 

One thing that you can do to help the extension speed of the piston is have 2 cylinders and some form of latch. The large cylinder you will punch the ball with is set up so that the latch will prevent it from extending until the smaller cylinder releases the latch. This way you can run air through the solenoid into the large cylinder to "pre-pressurize" it then release the latch. With the air already in the cylinder and not having to flow through the solenoid it should extend faster because it is not limited by the flow through the solenoid.

Re: Flow control?
 

In 2008 team 1108 used large pneumatic cylinders to catapult the ball by holding the catapult frame down with hard-drive (neodyniem) magnets. The pressure built in the cylinders to about 50 psi before the magnets were overcome, then the whole thing gives at once.

you could also do this by 'vacuuming' the ball down as a latch or even put a car-door-type latch on the catapult. When the cylinders are pressurized you open it.

But I think the magnet thing is easiest.

Re: Flow control?
 

In addition to the many other good suggestions in this thread: use as many cylinders as you reasonably can. Many small cylinders can be driven by many solenoid valves, increasing flow.

For random mechanism A you could use a single 1.5in cylinder or four 0.75in cylinders, both generate the same total force. Assuming all else is equal (i.e. factors IndySam brought up) the 0.75in cylinders will actuate about 4x faster because they will flow through 4 valves instead of just 1 on the 1.5in cylinder.

If using multiple cylinders it would be optimal to have numerous connections to your storage tanks, multiple norgren regulators, and the shortest possible tubing lengths. However, this might not be necessary.

In 2008 my team shot the 40in exercise ball with a two-stage direct-acting pneumatic launcher. Each stage had four 10-12in stroke 3/4 bore air cylinders. Each cylinder had its own solenoid valve.

Re: Flow control?
 

What types of tubing can we use? Can we use copper piping for our entire system if we want?

Also how do I post a new thread?

Re: Flow control?
 

There is a rule that dictates what tubing we can use. You should look it up.

Re: Flow control?
 

The rule says functionally the same with the inside diameter set. But does that include copper? It is functionally the same, but it does not act the same.

Re: Flow control?
 

The way to read the FRC rules is as follows:

If it is not specifically banned or otherwise disallowed, it is permitted.

Now, the pneumatics rules specifically state that anything that is not specifically permitted is prohibited. Copper tubing, however, would probably fall under the pneumatic tubing (though note: it should be sold as pneumatic tubing if you want to make life a little easier at inspection).


That said, CD is not the Q&A. I suggest asking the Q&A.

Re: Flow control?
 

I am brand new to this Chief Delphi stuff. How do I ask the Q&A? (this is our team's second year and I am the new rule master)

Re: Flow control?
 

http://www.usfirst.org/sites/default...m_User_Q-A.pdf (Linked from http://www.usfirst.org/roboticsprogr...c/game-q-and-a )

Q&A is located at https://frc-qa.usfirst.org/Questions.php.

Short version: Whoever has the TIMS access has the password to the account.

Re: Flow control?
 

Your Main or Alternate Contact has the User ID and password to login to frc-qa.usfirst.org in TIMS.

Don't post questions on multiple threads, it can be confusing.