Mulit-postioning with pnuematics this year?

[ngreen]

Originally Posted by ahecht

We would all agree that using the 66PSI wouldn't be legal, but I don't think you will get a consesus that just having it there as a side-effect of use is illegal.

I agree with ahecht here. It is only controlling what air we exhaust and what air we keep. We used this system all last year and we have never had any concern of safety or legality of the system. Looking on it after the facts presents it may occasionly run a few psi above 60. All the pneumatics are rated for 125 psi for these reasons. I honestly don't have any problem with anyone who runs this system at full capacity and occasionly has air go above 60 psi, only when you are extending the cyclinder. I take the word "working" air as the air coming from the regulator through the solenoids which is definitely 60 psi and not out the exhaust. The exhaust is not working rather it is being worked upon. If you route it through another solenoid to run another cyclinder then it is working and above 60psi and illegal. But these are just my view.

Good luck to anyone trying to do this. Also, generalbrando, would putting an air tank in series with the exhaust be useless because then you lose the capacity up the line in the 120psi section and limit your ability to move large loads farther? We are only allowed 2 air tanks. I guess you could just use a lot of the tubing and practically make a storage tank.

[Gary Bonner]

It seems to me that the pressure in these setups can go much higher than 60 psi, and the proposed remedies would not necessarily work.

Take the 2” cylinder example from before to somewhat of an extreme, but with no change in the load the piston is lifting. The surface area of the extend side of the piston is 3.14 in^2, and the retract side is 2.83 in^2. Suppose we are using the cylinder to lift 180 lbs. The extend side is pressurized to 60psi and the retract side is vented to the atmosphere. This produces a lifting force of 188lbs (60 psi X 3.14 in^2). When the piston gets to the height we want, we close the retract port. The extend side remains at 60 psi and exerting a 188 lb force on the piston. This is balanced by the 180 lb load on the piston plus the equilibrium pressure reached in the exhaust side, in this case, 2.8 psi ( 8 lb / 2.83 in^2).

Now, suppose we want to lower the piston a little. We pressurize the retract side to 60 psi and vent the extend side to the atmosphere. When it gets to the desired position we close the extend port. Now the retracting force on the piston is 350 lbs [180 lb load + (60 psi * 2.83 in^2)]. To counteract this force, the extend side becomes pressurized to 111 psi (350 lbs / 3.14 in^2).

In this situation, a venting regulator on the exhaust would merely act as a flow control valve and allow the piston to slowly move. Reducing the supply pressure wouldn’t necessarily help either.

If the load on the cylinder was in the other direction (e.g. we are pulling our robot up on the bar) the pressure would be greater. Also, any change in the load after we stop the piston (e.g. a robot hanging above slips down on us) would change the pressure on the exhaust side.

[KenWittlief]

the extend side becomes pressurized to 111 psi...

that is not possible with the drawing I posted. As soon as the secondary regulator sees more than 60 psi on its output side it will vent it until the pressure drops to 60. not gradually, instantly.

its the same as if you use the pneumatics as defined in the manual - if you have a large cylinder pointing forwards on your bot, extended - and you drive into a wall at high speed, as the cylinder is pushed in the regulator vents the excess pressure - thats what they are for. they keep the pressure on the output side at the set level, no matter what happens to the cylinders.

[Leo M]

Look at page 4 of the 2004 Pneumatics Manual. The primary pressure regulator, the Norgren, is required in-line right after the tanks to limit the working pressure to 60 psig. This is a "relieving regulator" - if the pressure on the downstream side (cylinders & solenoid valves) increases above 60 psig - say, by pushing on an arm actuated by a cylinder - the regulator will relieve the pressure by venting air. There is no need to jump through hoops to limit working pressure to <= 60 psig; the main regulator takes care of that automatically.

Now, while you have the manual out, why not read the entire thing thoroughly, so you understand how all of the components work together? It will pay off in the long run, only takes about 30 minutes, and will save pages of posting.

[ngreen]

Originally Posted by Leo M

Look at page 4 of the 2004 Pneumatics Manual. The primary pressure regulator, the Norgren, is required in-line right after the tanks to limit the working pressure to 60 psig. This is a "relieving regulator" - if the pressure on the downstream side (cylinders & solenoid valves) increases above 60 psig - say, by pushing on an arm actuated by a cylinder - the regulator will relieve the pressure by venting air. There is no need to jump through hoops to limit working pressure to <= 60 psig; the main regulator takes care of that automatically.

Now, while you have the manual out, why not read the entire thing thoroughly, so you understand how all of the components work together? It will pay off in the long run, only takes about 30 minutes, and will save pages of posting.

Yes on the side between the regulator and the side of the cyclinder that is open. If you have this side open and the cyclinder is fully extended and you push it back. Air over 60 psi will be forced out of the regulator.

However on the other side of the cyclinder to where the air is stopped there is no release and there is a possibility that it will go a little over 60 psi as much as 66 psi. This would occur during a stop during an extension. During a retraction this problem wouldn't occur because of the norgen relief valve.

And don't think that reading the manual will give you answers to many of these problems. The manual is very vague and only give you very little info other some of the capabilities and pictures so that rookies will know what to look for in the kit. I am sure these people like myself have read the manual and rules several times over and have a good general idea of what to look for but the only way you can be for sure is if you hook it up and test it.

[KenWittlief]

the subject of this thread, using pneumatics in a way that will allow you to stop a cylinder between the ends of its tavel, and keep it there,

is not covered in the pneumatics manual

we are being clever with the way the cylinders are used, and blocking the vent side (that is normally open to the the room pressure)

thats why this thread is going on 4 pages - we are trying something new and want to make sure we dont:

1. violate any design rules or

2. create a system that could be dangerous

so far, I think we are on solid ground.

maybe next year the results of this thread will be IN the manual - it wouldnt be the first time that teams got so innovative that FIRST had to re-write the book :c)

[Astronouth7303]

Exuse me, but I was just poking my head in, metaphorically, and I saw this. We're doing it too. Were just taking a solenoid (the curved half-circle) and placing it before the 'memory' solenoid, which is connected to the cylinder. We haven't gotten it to work, yet, but I think that's a coding issue.

I've said my peice. I'm going back to my regular place now.

[M. Hicken]

does anyone think that you could mount a limit switch accordingly to where you want the cylinder to stop, thus it would kill power to the soleniod, would that work? I know it is not the best design, im just curious

[Biff]

Originally Posted by M. Hicken

does anyone think that you could mount a limit switch accordingly to where you want the cylinder to stop, thus it would kill power to the soleniod, would that work? I know it is not the best design, im just curious

Depending on how you plumb the hoses you will just send the piston the other direction. You are going to have to test things or figure them out by drawing the air flows in each state for the valve wiht power on and off. The short answer to your question is no.

[ngreen]

Originally Posted by Biff

Depending on how you plumb the hoses you will just send the piston the other direction. You are going to have to test things or figure them out by drawing the air flows in each state for the valve wiht power on and off. The short answer to your question is no.

This is wrong. With this you could definitely do this. You can program the limit switch to change the single solenoid to its stopped state and stop the cyclinder. Yes, this would work. Any questions about set-up of the pneumatic parts refer to my diagram or ask me. The pistons will stop if you do it right, thus multi-positioning.

[ngreen]

Originally Posted by Astronouth7303

Exuse me, but I was just poking my head in, metaphorically, and I saw this. We're doing it too. Were just taking a solenoid (the curved half-circle) and placing it before the 'memory' solenoid, which is connected to the cylinder. We haven't gotten it to work, yet, but I think that's a coding issue.

I've said my peice. I'm going back to my regular place now.

Refer to my diagram as writing on the first page and set it up exactly like it. You hook the single solenoid (curved one) after the "memory" solenoid. The curved solenoids input 1 should be the combined exhaust of the memory solenoid. Make two stops using 2 pieces of tubing and a tee on each. Put these stops on output 2 and exhaust 4. When you have this setup. Power the system and check for leaks, they do make a difference. When there are no leaks switch the memory solenoid either direction it needs to go using the two manual buttons on top. The solenoid will switch but the cyclinder won't move. Then using a finger or a screw-driver, switch the manual switch of the curved solenoid and let go. The cyclinder should go in the direction the memory solenoid selects and then stop when you let off of the manual switch of the curved solenoid. Once you get this to work and see what need to be activated or unactivated to move the cyclinder in this way and program that into a single button, multiple buttons, and single switch or a series of switches. Whatever works best. If you have questions just ask. Again the diagram is the exact one we used last year, look at the robot side and you can see the controlled cyclinder. If I find any pictures of our pneumatic board from last year I will be sure to post it. Good Luck!

[Chris Fultz]

Some follow-up /

First, this does work and we have tried it out on our 2003 robot. very controllable. One thing, you have to cycle full up and down a few times to charge up the whole system with compressed air. Then it is stable.

While experimenting, dial in the fittings to be very restrictive - it wil slow everything down and it is easier to see the efects of what you are doing.

Also, I added a pressure gage in the line. It never went above 60 psi. I don't think that is right, so I am going to change around the gages and see if it is just gage error. The math says it should be > 60, but maybe tiny leaks and volume keep it from reaching that high.

We used 2 switches. On double action to the the dual solenoid. selecting left or right will define the direction the cylinder travels. The second switch is a momentary on that is connected to the single solenoid. Pulses on this switch vent the cylinder and it moves in the direction set by switch 1.

Our programmers are trying to set up the control to do this. We are going to try some limit switches or something and see if we can stop it automatically with the control.

I have a power point slide that we used tonight in our design review. If someone can tell me how to add it to a post I will insert it. It makes it pretty clear and easy to convince the non-believers.

Like I said in an earlier post - this is awesome and thanks for sharing the idea.

[ngreen]

Chris,

Maybe you can add the powerpoint to the whitepapers and put a link from the post. That would be great. Good luck and be sure to mention anything new you find.

Thanks,

[Leo M]

Mr. Green, you are quite correct. I completely mis-interpreted the issue. Bottling up the pressure by plugging a solenoid vent port and then pushing on the cylinder will indeed raise the pressure beyond 60 psig. The regulator would never see it, being isolated from that section of the system.

Further proof - if more were needed! - that the world is a better place when FIRST and I pursue divergent pathways. I shall return to obscurity and live by the strict abstinence principle, henceforth eschewing all things robotic.

[Biff]

Originally Posted by ngreen

This is wrong. With this you could definitely do this. You can program the limit switch to change the single solenoid to its stopped state and stop the cyclinder. Yes, this would work. Any questions about set-up of the pneumatic parts refer to my diagram or ask me. The pistons will stop if you do it right, thus multi-positioning.

We are both right to a point, I took the original question as to just cutting off the power to the "memory" solenoid. If that was the case I was correct in saying that it would nor work. You are correct if it is a single action soleniod working with the "memory" soleniod. All you are using the switch for is to let the program know when to cut the air at the single solenoid. Peace.