Pneumatics Resources
 

Hi, I'm kind of new with Pneumatics and was wondering if anyone had any resources they used besides the Pneumatics Manual by FIRST. What I'm looking for really are the methods and calculations used to perform some kind of pneumatic task, in particular with an arm assembly.

Also, I was wondering if anyone had developd a system for controlling the position of the extension of the piston on a cylinder. I found one idea on CD but it used 2 solenoid's, has anyone implemented this concept with just one solenoid?

Thanks,
David

Re: Pneumatics Resources
 

As for resources regarding pneumatics, I would say that the best place to start is on CD. Look into whitepages and the pneumatics section. I would have to personally suggest some of the powerpoints that are up there. In regards to getting a hands on insight, look into some of the theater companies around you. My pneumatics knowledge came first hand from an animatronics expert. But again the best way is just to go and try it.

Ok now multi positioning....

My team did multi positioning out rookie year and it worked ok. The only real way to do it is with two solenoids. I personally would not suggest it as a solution for any problem though. But if you are interested in pursuing that route feel free to ask any questions and I would be happy to answer them.

Re: Pneumatics Resources
 

Whoa, another team that tried mid positions their rookie year! And to the best of my (limited) knowledge, you need to use two solenoids. One controls the direction of the movement, and an upstream solenoid with the exhausts blocked either lets air into the piston or holds it in place. But learn from our mistake - you really don't want to. The pneumatics are designed to be either all the way in or all the way out. What we forgot is that air will compress, and so if you try and hold a piston in the middle, any changing forces on the piston will cause the position to change. We made an articulated arm using only pneumatics last year that we had to remove due to massive weight problems, but it was entirely uncontrollable. I'm sure others could do a much better job, but pneumatics are really not the best choice if you want any positions other than all the way in or all the way out.

As for resources? The FIRST pneumatics manual is the best starting place, which you already found. You should also look at Bimba, the supplier for pistons for FIRST. Speifically, look at the Original Line Cylinders catalog. Only certain piston sizes are FIRST legal, but it should give you an idea of what is available and how to choose pistons. The force provided is a function of the bore size and line pressure, which is regulated to 60 psi on FIRST robots. Therefore, knowing the force required and the required stroke length should be all you need to know to choose a cylinder.

Re: Pneumatics Resources
 

Here's a recent artice I ran across on the topic about new valves coming on the market to do just that.
http://machinedesign.com/ContentItem...actuators.aspx

As Daniel points out, the compressibility of air is a problem in holding the position. The air in the cylinder acts like a spring and the piston moves as the external forces change. To counter this, you need a feedback mechanism so the valve can rapidly adjust the pressure in the cylinder. Being able to integrate the control electronics into the valve makes it a reasonably priced commodity.

Re: Pneumatics Resources
 

We set up our pneumatics tonight as what I could discern from the powerpoint on CD, but couldn't get the piston to stop at an arbitrary point, only at the ends of its stroke. We worked on it for about 3 hours in many different configurations but couldn't get any good results. I understand that the concept is to control the exhaust pressure, but since I am fairly new to this system I am having some difficulties. I assume my problem is the setup I used. Can you give an exact explanation of the pneumatic, wiring and component connections to use? Also, could you provide an example of the C code you used as well? Thanks, I appreciate it.

Re: Pneumatics Resources
 

With the equipment we are given, you only get the ends of the stroke (all the way open or all the way closed). Teams have tried to regulate pressure to get it to stop at arbitrary points, but I don't think any have done it successfully.

However, there are pistons and solenoids on the market that can do that no problem; they're just not legal in FIRST.

Re: Pneumatics Resources
 

I went to a workshop and 339 has done it successfully. I need to check it out more to fully understand it though.

Re: Pneumatics Resources
 

We had and arrangement that kinda-sorta worked for mid positions. I'll try and describe it. (This is from memory, and could be slightly wrong.)

Take one solenoid and plug an exhaust port. Connect the output of this solenoid that uses the plugged exhaust port to vent to the input of another solenoid. The other output of the first solenoid needs to be plugged to prevent venting the supply line into space. The outputs of the second solenoid go to the piston. To extend the piston, set the second solenoid to the direction that will extend the piston, and set the first solenoid to let air into the second. To retract, do the same but with the second solenoid in the other position. To stop movement, set the first solenoid so that the air supply is output to the plug and the exhaust from the second solenoid and therefore the piston is exhausted to a plug, which should trap air in one side of the piston. It may be beneficial to flip the second solenoid when you stop to keep air in the side of the piston that pushes outward trapped instead of the side that pushes back. Sorry for this being so confusing, but I can't think of a better way to express my crazed thoughts.

I'll try and draw a diagram (let's see if my ASCII-fu is with me today):
Again, I'm not quite sure if this is exactly what we did, some of the plugs may have to be in different places. I can't remember the exact workings of the solenoids right now. It was never a good idea to start with. I feel it needs repeating (since we missed this obvious fact last year) that air will compress, making the piston movable even when stopped with this type of control. The movement from my harebrained scheme is jerky and hard to use. Lastly, completely overshadowed by the other problems, any leaks will also affect the piston more as it will not be recharged by the compressor / supply until it is moved again.

All that said, it is a way to achieve mid positions with FIRST legal parts. One last point is that it will help to apply a force to the piston so that there will be something to keep pressure in the piston when it is in midstroke, such as a bungie cord attached to the piston's end that will constantly pull it back (an idea one of our mentors came up with to save my unworkable midstroke arm controls).

And lastly, I have to say that I would never recommend this setup as a viable solution. It is way too much of an ugly, inherently uncontrollable hack. The arm based upon this idea never worked well enough to use effectively (and was removed before competition due to weight problems.)

Re: Pneumatics Resources
 

Your diagram doesn't make sense, don't you need a solenoid on one of the exhaust ports from the cylinder control solenoid. Anyway - it's not a great solution.

Here's something I see once in a while... Connect two cylinders together!! Maybe a 4 inch with an 8 inch. Now you have a multiple length cylinder (rather long!!) that can extend 4", 8", or 12".

Re: Pneumatics Resources
 

I was there too. They used a three solenoid valve with some sort of inline valve (I think). it allowed varying positions with very little slop. Can someone from 339 comment?

Re: Pneumatics Resources
 

WPI 2007 Resources have a couple presentations on Pneumatics

Re: Pneumatics Resources
 

Using kit solenoids, You need two. One for direction, which you hook up normally. Then you connect the vents from the first valve to a second, to stop the air from venting to the atmosphere. This stops the cylinder from moving until this second valve is opened.

Program the first for direction, the second for movement(on/off)

Lots of info in this thread, with a diagram on 11th post:
http://www.chiefdelphi.com/forums/sh...ght=pneumatics

Re: Pneumatics Resources
 

Well I setup the system as has been described by more than a few threads on the last post, but I'm not having any luck still. I used this code:

if(p2_sw_aux1 == 1)
{
relay2_fwd = 1;
relay2_rev = 0;
relay3_fwd = 0;
}
if(p2_sw_aux2 == 1)
{
relay2_fwd = 0;
relay2_rev = 1;
relay3_fwd = 0;
}
else
{
relay3_fwd = 0;
relay2_fwd = 0;
relay2_rev = 0;
}

When I set it up, the piston will still immediately extend even if the button is immediately let go. Now I am using 2 double solenoids, (is this a problem?) So when I try it the other way (i.e. changing the side that is blocked or changing the side that relay3 is on) it moves a little bit then stops and won't move again. I assume this is because the exhaust is blocked on the wrong port so it moves a bit while the stop(a loop) is charging. After going back to the original setup I tried changing the speed with the SMC speed regulators and although it slowed it down a lot it wouldn't stop completely. Anyone have any ideas what I'm doing wrong?

Items of interest:

My system setup requires that the first double solenoid side B be wired up backwards in order for the piston to retract, it required this without using the second exhaust-blocking solenoid. Is there a problem with this?

As stated before, I am using 2 double solenoids, is there a problem with this?

During operation, when aux1 is pressed relay2 goes green and relay3 goes green. When aux2 is pressed, relay2 goes red and relay3 goes green. when no button is pressed, both relays are orange. the colors on the solenoid light up appropriately when the relays are actuated. So I assume the programming and the wiring up to the relays is correct.

Re: Pneumatics Resources
 

Since you are using two double solenoids, you are going to have to wire up both sides of the second solenoid to relay 3 like you did the first solenoid to relay 2. As I only see relay3_fwd in your code and only one side hooked up in your diagram, I'm guessing that this is at least some of the problem. Otherwise, the second solenoid will never switch back to venting, and never allow the piston to move. Also, in the code snippet, relay3_fwd is never set to 1, which seems to be inconsistent with your description of what happens but does make the logic a little harder to trace.

Also, your diagram shows both positive and negative connections from the solenoids going to the relays, when if I remember correctly the correct way to wire solenoids is to have the positive go to the spike and the negative directly to ground. This way, you can control two solenoids with the same spike by connecting one to M+ and another to M- on the spike. (Yes, both positive and negative terminals can be positive at the same time on a spike. They are strange little things. See http://www.ifirobotics.com/docs/spik...uide-sep05.pdf for a diagram and explanation of this.)

Anyways, I like what you are attempting where the piston always has pressure on both sides way more than my old design where one side vents when it is being "held" in place. So to anyone who sees this thread in the future, try this instead! :)

Re: Pneumatics Resources
 

Sorry that was a typo in the code, in the first two if statements it should be relay3_fwd = 1. I'll try making your suggestions tonight, thanks!

Re: Pneumatics Resources
 

If your mid-cyllinder positioning does not have to be exact, you can use what Team 339 used in their offseason scrimmage bot -- a pilot-operated check valve. This valve came with the '01 or '02 KOP. It looked pretty tricky to hook all the tubes up to, but the good news is that you do not need a potentiometer or double solenoid valve -- the check valves mount directly to your cyllinders and use a single-solenoid valve that operates from a spike.

They work great and have fast enough response times for a driver to manually work the pneumatic cyllinder and stop in the middle of the cyllinder with enough accuracy. They do not work well in autonomous, so the piston would have to be all the way out or all the way in.

They work using air pressure -- essentially the two ports on the cyllinder are tubed/hooked up in such a way that air cannot go in one side without a change in air pressue from the other side. Since the spike can cut power to the solenoid at any time (therefore it will no longer change the pressure of the cyllinder subsystem after it) the cyllinder stops whenever the spike cuts power -- i.e. in the middle of the cyllinder.

It even sounds pretty cool to hear it in action -- it's like a slow-shooting paintball gun.