Fragen und Experimente zur Pneumatik / Questions and experiments with pneumatics

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rubem
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Fragen und Experimente zur Pneumatik / Questions and experiments with pneumatics

Beitrag von rubem » 09 Jun 2021, 01:30

Hi everyone,

I'm assemblying a pinball table similar to the one in the Electropneumatics kit. This project has some challenges for me, the main one being that I'm a complete novice on pneumatics :shock: But thanks to you guys, this forum and the picture pool, I've been able to understand enough to get it working so far. The model is not identical to the Electropneumatics kit because: 1) I don't own the kit itself; 2) Some pneumatic parts are the classic Festo ones and 3) Some parts are non-ft, see here:

Non-ft.png
Non-ft.png (202.62 KiB) 1137 mal betrachtet

The two small 3/2-way 5V solenoid valves behave similarly to the ft ones. I've included a voltage regulator on each and now I can operate them from 9V. They work well with the TXT or directly via a push-button. I'm also using 2 membrane check valves (shown above) between the compressor and the solenoid valves so that each one has its own separate air reservoir (a blue cylinder). I'm not using the big 2/2-way solenoids for now.

I don't have any red pneumatic cylinders, so I'm using an old 45 mm Festo cylinder with spring for one flipper. It works well. For the other flipper I used a leaking Festo cylinder 45 which I've pried open (someone already did it in the past, it had a lot of glue), cleaned it up very carefully, inserted a (different) spring and sealed it back with hot melt glue so I can work on it again if necessary. It has good performance, but it extends a bit less because of the different spring. Playable, but not great.

I'm still experimenting with cylinders. I took a very stiff blue cylinder, pried it open and removed the gasket/O-ring so it became a single-acting cylinder, and runs much smoothly. Then I inserted another spring in it and sealed it with hot melt glue, so it became a "red" cylinder. However the spring is too strong, so it requires extra force and the movement is too slow for pinball.

What I really want is to be able to extend and retract the cylinders pneumatically. This way I could use cylinders without springs, which would be ideal for maximum force. I learned that this can be done using an extra 3/2 way valve for each cylinder, but I don't have them, my pneumatics inventory is quite modest. I have two strong 2/2-way valves (see above), two air tanks, some old Festo valves and Festo actuators. Is it possible to accomplish this with the parts I already have?

Thanks a lot in advance for your help and patience with this "pneum-newbie".

Warmest regards to all,

Rubem

P. S. I use a blue ft compressor via a relay that connects it directly to the 9 V supply. The TXT outputs provide a lower voltage and the airflow decreases significantly.
Zuletzt geändert von rubem am 09 Jun 2021, 23:15, insgesamt 1-mal geändert.

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steffalk
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Re: Fragen und Experimente zur Pneumatik / Questions and experiments with pneumatics

Beitrag von steffalk » 09 Jun 2021, 10:30

Hello Rubem,

You can construct a 3/2 way valve from two 2/2 way valves. For each side of a cylinder, you need one 3/2 way valve. You can construct them like this:

[Air pressure] --- [2/2 way valve] --- [One cylinder end] --- [2/2 way valve] --- [free air]

The two valves are connected to the same pin of the cylinder. Open exactly one of them at a time: One to get air into the cylinder, the other to get it out again.

The alternative is one 4/2 way valve: 4 ways (one for each pin of the cylinders, 1 for the compressor, 1 for the free air output) and 2 positions (cylinder expanded or shrinked).

You can construct such valves on your own using nothing more than standard fischertechnik parts! See "Druckluftsteuerungen (Teil 1)" (pneumatic controls, part 1) in ft:pedia: https://ftcommunity.de/ftpedia/2014/201 ... df#page=58. While the text is written in German language, I guess you can see everything needed in the pictures. If not, feel free to ask here.

Best Regards

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Re: Fragen und Experimente zur Pneumatik / Questions and experiments with pneumatics

Beitrag von rubem » 09 Jun 2021, 23:30

Hi Stefan,

Many thanks for your quick answer! With some effort I was able to translate most parts of the ft:pedia article, and I find the idea of clamping/kinking hoses to control the airflow simply brilliant. Although I suspect that this kind of solution is better fit for more experimental models (they also take a lot of precious space), the idea of DIY valves is intriguing, maybe I'll test it, let's see.

In the end the simplest / most compact way would be to purchase two additional 3/2 valves anyway...

Thanks again,

Rubem

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Re: Fragen und Experimente zur Pneumatik / Questions and experiments with pneumatics

Beitrag von rubem » 10 Jun 2021, 14:38

Hi again,
rubem hat geschrieben:
09 Jun 2021, 23:30
In the end the simplest / most compact way would be to purchase two additional 3/2 valves anyway...
...I just ordered the two extra valves :D

Meanwhile I have another question: I wonder why my blue ft compressor is so noisy to the point of being annoying, is this normal? Could it be that it became noisier after only several hours of usage (not continuously)?

Greetings,

Rubem

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Re: Fragen und Experimente zur Pneumatik / Questions and experiments with pneumatics

Beitrag von steffalk » 10 Jun 2021, 15:36

Hello Rubem,

I have several of the blue ft compressors, and I find them loud when they are attached very fix to a model, standing on a table giving resonance. I usually fix them on ft springs and not directly to any model. It is really the compressor itself that is so loud, or only if it is built into a model? If it is loud by itself, it may well have some damage.

Regards,
Stefan

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Re: Fragen und Experimente zur Pneumatik / Questions and experiments with pneumatics

Beitrag von rubem » 10 Jun 2021, 16:00

steffalk hat geschrieben:
10 Jun 2021, 15:36
Hello Rubem,

I have several of the blue ft compressors, and I find them loud when they are attached very fix to a model, standing on a table giving resonance. I usually fix them on ft springs and not directly to any model. It is really the compressor itself that is so loud, or only if it is built into a model? If it is loud by itself, it may well have some damage.

Regards,
Stefan
Good catch! Yes, in fact the compressor is very firmly attached to the model and there are lots of BS30s in contact with the desk surface, so probably my whole desk resonates. I recall having seen the trick with the ft springs in one of your models from the picture pool. I don't have any plastic ft springs, but I have several springed feet #31307, maybe they help. I'll make some tests this weekend to determine if I can pinpoint the cause.

Thanks again,

Rubem

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Re: Fragen und Experimente zur Pneumatik / Questions and experiments with pneumatics

Beitrag von H.A.R.R.Y. » 10 Jun 2021, 17:26

Hello,

it does not need to be ft always and everywhere. If you just want to decouple the vibrations of the compressor you could use simple rubber bands and fix them into an ft frame. More stable and durable might be some rubber bands with some surface clothing like hair ties, elastic waist band, ...

The compressor itself usually does not put problems since it is connected by flexible wires and hoses. The only two things you really want from its fixture:
  • Stay were it is.
  • Do not rotate due to its inertia.
Cumprimentos
H.A.R.R.Y.
[42] SURVIVE - or die trying

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Re: Fragen und Experimente zur Pneumatik / Questions and experiments with pneumatics

Beitrag von rubem » 10 Jun 2021, 17:44

Hi H.A.R.R.Y,
H.A.R.R.Y. hat geschrieben:
10 Jun 2021, 17:26
it does not need to be ft always and everywhere
Yes, I also think that way. I think I have some black rubber foam pieces in the storage area, they'll probably look better than my yellow rubber bands (looks are important). Maybe I'll use them if the mold odors are not too strong :D

Thanks for the ideas!

Abraços,

Rubem
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Re: Fragen und Experimente zur Pneumatik / Questions and experiments with pneumatics

Beitrag von rubem » 15 Jun 2021, 16:36

Hi Stefan and H.A.R.R.Y,

Simply placing four self-adhesive silicone discs under the pinball table feet reduced the noise significantly, so my conclusion is that there is nothing wrong with the compressor. My desk was just resonating and amplifying the noise. I will still experiment with foam rubber when I have the time, and I'll post the results here.

Thanks again,

Rubem

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Re: Fragen und Experimente zur Pneumatik / Questions and experiments with pneumatics

Beitrag von rubem » 21 Jun 2021, 01:25

Hello everybody,

I'm back to the experiments with pneumatics for my pinball table. I feel more newbie than ever :cry: I supose I understand that a conventional circuit (e.g. from the ElectroPneumatics kit) should be like this:

Conventional circuit.png
Conventional circuit.png (84.87 KiB) 693 mal betrachtet

(I intend to use two check valves so the air reservoirs are independent for each flipper, I hope it makes sense.)

However... The only springed actuators I have are two old 45 mm Festo ones. The springs reduce the power and the actuators don't really don't go back to the start position, that's why I want to use pneumatics to move the actuator back. I've removed the O-ring from a conventional blue cylinder so it became a single-acting one. I've inserted a spring in it but it also didn't perform well. By removing the spring it becomes quite powerful:

Incomplete circuit.png
Incomplete circuit.png (85.3 KiB) 353 mal betrachtet

Of course this circuit only goes forward, so I've tried this:

Failed circuit.png
Failed circuit.png (104.81 KiB) 693 mal betrachtet

It goes back and forth, but it's ridiculously slow in both directions. Of course this is not what I need. I suppose that once I get it right, I'll want to move the actuator back just for some half second or so, then turn off both solenoids. Anyway I need your help here! I've even created an empty circuit with labels:

Empty circuit.png
Empty circuit.png (101.79 KiB) 693 mal betrachtet

Thanks for any help,

Rubem


P.S. I'm giving away my personal collection of 2-D ft parts as a prize for those who help me find the solution :D :D
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Re: Fragen und Experimente zur Pneumatik / Questions and experiments with pneumatics

Beitrag von steffalk » 21 Jun 2021, 09:24

Hello Rubem!

I would say your circuit is perfectly correct and just wonder why you connected the right valve *before* instead of after the check valve. Why not put both behind it? What is the sense of the check valve? You may as well just remove it, I guess.

Good luck,
Stefan

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Re: Fragen und Experimente zur Pneumatik / Questions and experiments with pneumatics

Beitrag von rubem » 21 Jun 2021, 15:08

Hi Stefan,
steffalk hat geschrieben:
21 Jun 2021, 09:24
I would say your circuit is perfectly correct and just wonder why you connected the right valve *before* instead of after the check valve. Why not put both behind it? What is the sense of the check valve? You may as well just remove it, I guess.
Yes, the check valve is optional at this point. The idea is to create two separate air reservoirs, one for each actuator. I've already tried it like you say (below), but the results were the same: the actuator moves slowly in both directions.

Failed circuit 2.png
Failed circuit 2.png (99.78 KiB) 587 mal betrachtet

Thanks,

Rubem

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Re: Fragen und Experimente zur Pneumatik / Questions and experiments with pneumatics

Beitrag von steffalk » 21 Jun 2021, 15:26

Hello Rubem,

this sounds strange to me. Could you please try

- leaving the air reservoir away entirely,

- use a larger air reservoir (one of the fischertechnik parts) and, more importantly, feed the air into the reservoir from one side and use another pin as output (not possible with a cylinder), or, finally,

- double check everything for leakages, check that the compressor is running with 9V.

As this is one of the most simple setups you can use a cylinder with, this should run absolutely fine.

Regards,
Stefan

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Re: Fragen und Experimente zur Pneumatik / Questions and experiments with pneumatics

Beitrag von rubem » 21 Jun 2021, 15:49

Hi again,

Thanks for the check list!! My answers:

1) leaving the air reservoir away entirely: Didn't try that, I will.
2) use a larger air reservoir (one of the fischertechnik parts) and, more importantly, feed the air into the reservoir from one side and use another pin as output (not possible with a cylinder): Will do, I have a pair of old blue air tanks.
3) double check everything for leakages: there is an expected leakage from the B inlet of the actuator, since I removed the O-ring. Other than that, I believe I've checked the connections several times.
4) check that the compressor is running with 9V: Yes, it is connected directly to the power source, a 9V / 3A switching adapter.

As a reminder, I'm not using fischertechnik solenoid valves, but the miniature 5 V valves shown at the first picture above 👆🏻 on the left. They are rated at around 0.5 bar. Maybe that's the problem?

Thanks again!!!

Rubem

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Re: Fragen und Experimente zur Pneumatik / Questions and experiments with pneumatics

Beitrag von steffalk » 21 Jun 2021, 16:30

Hello Rubem,
there is an expected leakage from the B inlet of the actuator, since I removed the O-ring
Can you use a fully intact cylinder? Leakage, expected or not, is no good ;-)
They are rated at around 0.5 bar
This may be a problem as well as it may not be a problem. Could you try the hand-driven black/blue valve https://ft-datenbank.de/ft-article/3225 to test? Connect the compressor to the middle pin and the pins of the cylinders to the other two.

Regards,
Stefan

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Re: Fragen und Experimente zur Pneumatik / Questions and experiments with pneumatics

Beitrag von rubem » 21 Jun 2021, 16:47

Hello Stefan,
steffalk hat geschrieben:
21 Jun 2021, 16:30
Can you use a fully intact cylinder? Leakage, expected or not, is no good ;-)
I did that. The blue cylinders I have are very stiff so they move slowly no matter what. That's why I removed the O-ring from one of them in the first place.
This may be a problem as well as it may not be a problem. Could you try the hand-driven black/blue valve https://ft-datenbank.de/ft-article/3225 to test? Connect the compressor to the middle pin and the pins of the cylinders to the other two.
No, but I'll do that. I'll return here with more results as soon as I can.

Meanwhile, thanks a lot for your help!

Rubem

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Re: Fragen und Experimente zur Pneumatik / Questions and experiments with pneumatics

Beitrag von steffalk » 21 Jun 2021, 17:11

Hello again,
The blue cylinders I have are very stiff so they move slowly no matter what
Sounds like the cylinder is not oiled enough. It should go smoothly and quite easily by hand. If not, try another (new?) cylinder, or make it go smoother. But remember that only a few liquids are valid for the plastics. You can use, for example, *one (!) drop* of "Medizinisches Weissöl" ("medical white oil" in direct translation, but it may have a total different name in English).

Success,
Stefan

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Re: Fragen und Experimente zur Pneumatik / Questions and experiments with pneumatics

Beitrag von rubem » 21 Jun 2021, 18:59

Hi,
steffalk hat geschrieben:
21 Jun 2021, 17:11
Sounds like the cylinder is not oiled enough
I once lubricated some of them with silicone oil. It kinda worked, but the oil wore out quickly and they went back to their normal state. Then I had the idea of removing the O-ring and inserting a spring, but the spring was too strong. Oh well...

Still experimenting... Something should work. Thanks!!!

Rubem

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Re: Fragen und Experimente zur Pneumatik / Questions and experiments with pneumatics

Beitrag von H.A.R.R.Y. » 21 Jun 2021, 20:42

Hi rubem,

your circuit switches both solenoids at the same moment. When one feeds pressurized air into the cylinder the other one just starts to leave this pressure out to ambient. The differential pressure across the piston is less than you might expect, and thus the resulting force that moves it. Could you take a second pushbutton and try this, please:
One pushbutton powers valve 1 (and if this is powered, the air is guided into the cylinder, otherwise the cylinder is conected to ambient). Then you release this pushbutton and without force to the piston the cylinder stays were it is. When you now power the opposite valve with another pushbutton this will feed the cylinder opposite side with pressure and this time there is no high pressure that needs to be pushed out while the piston moves also. Maybe this speeds up your cylinder movement? But I am not sure if all the hose, nozzle and solenoid valve holes have sufficient diameter to allow for large volume flows at low pressure loss. At least you might want to kepp all air connections (hoses) as short as possible to minimize dead volume.

But what do you intend? A kind of pneumatic catapult to shoot one steel ball into the flipper? Check the basic physics behind, to figure out what speed the piston needs to move and then how much pressure it would take to accelerate this complete mass against the coulomb drag of the piston. I have the feeling that ft-pneumatics might not fit this bill. I once tried to shoot a ping pong ball up an inclined track using "Betätiger" https://ft-datenbank.de/ft-article/3218. Well, the Betätiger responds way faster to pressurization than a cylinder but for me it was no success, although.

Regards
H.A.R.R.Y.
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Re: Fragen und Experimente zur Pneumatik / Questions and experiments with pneumatics

Beitrag von rubem » 22 Jun 2021, 15:10

Hello,

@Stefan, yesterday I disassembled my previously opened cylinders (both blue and Festo types) and oiled them with silicon oil again. Especially the Festo one became amazingly smooth, but after just one day I can see the oil is not so effective. Perhaps this is not the right one? The local drugstores have something called "óleo mineral" (mineral oil) which is used for dry skin and... constipation. Is this the one I should try? Consipation makes a lot of sense, hahaha :D :D :D

@Harry, I experimented with the setup you suggested (thanks for the idea!), using a separate switch for the second valve. You are right, the forward movement is much faster if the valve are not operated simultaneously. It works well if switch 1 is pressed for a very short time, but the speed to move the piston back is much slower after pressing it around one second or more. It this case it generates an audible "pfffft". It seems more pressure builds up while valve 1 is open. The natural next step here would be to code this behavior with an Arduino, maybe adding a reed sensor to detect the moment where the cylinder is fully extended and limiting the time valve 1 is kept open.
But what do you intend? A kind of pneumatic catapult to shoot one steel ball into the flipper?
My pinball table is quite similar to the one in the Electropneumatics kit and has the same size. The steel balls are identical to ft's (12.7 mm diameter) and I suppose they weigh just the same. (Edit: the seller just answered me, it's around 8.4 g.) However I don't have the original valves, cylinders and hoses (I'm using 2x4 silicon hose). The hoses between the valves and the cylinder are around 10-12 cm, that's much shorter than in the Electropneumatics kit (30 cm).
I once tried to shoot a ping pong ball up an inclined track using "Betätiger" https://ft-datenbank.de/ft-article/3218. Well, the Betätiger responds way faster to pressurization than a cylinder but for me it was no success, although.
Interesting! I have these parts too.

Still experimenting... Abraços,

Rubem

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