Fragen und Experimente zur Pneumatik / Questions and experiments with pneumatics

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

Beitrag von H.A.R.R.Y. » 22 Jun 2021, 16:51

Olá rubem,

here in this Forum we have got some kind of thread dedicated to pneumatic cylinder lubrication. Unfortunately for you it is in German language.
viewtopic.php?f=15&t=2236
There you find the lubricant recommended to be
Paraffinum perliquidum
And of course, very sparse application is recommended.
rubem hat geschrieben:
22 Jun 2021, 15:10
@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.
Well, that is really fine to hear. Instead of having the piston now pushing out the pressurized air of the other side you get it moving against ambient pressure (and some back pressure because some air still needs to move out for the piston) you now get maximum force. The way back is naturally different. The old (blue) cylinders lack some sealing gasket on the piston shaft. This is where always the air escapes to ambient ... pfffft. And this is where you loose pressure. I think you wrote something about new (black) cylinders where you removed this gasket? Anyway. The gasket on the cylinder head (where the shaft comes out) cause friction losses and thus slower speed. The highest piston speed you receive from high air pressure and leastmost friction losses. Oh, and by the way, I thought up to now that your cylinder starts the ball into the game. But now I see that the cylinders push the levers. Did you check that there is some gap between the levers and the base plate? The hinges also are with leastmnost friction?

The ball mass should be similar to those of ft. Basically they take the same diameter and material. It is just the speed (or better impulse (from momentum and conservation of momentum)) the ball receives.
rubem hat geschrieben:
22 Jun 2021, 15:10
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.
Just some experimental and fixed "valve 1 open" time, some delay and then the "valve 2 open" time should do. A Reed-Switch might be too much here.

Continuar a experimentar
H.A.R.R.Y.

PS: One thing I almost forgot. With your setup there is minimum to no pressurized air reservoir. Without sufficient storage capacity the pistons move at the rate the compressor pumps the volume. This is quite slow. Maybe you can convert some enmpty plastic bottle or something else into an "air tank". Something like on this picture https://ftcommunity.de/bilderpool/veran ... -27/39114/
[42] SURVIVE - or die trying

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

Beitrag von rubem » 22 Jun 2021, 17:30

Hi Harry,
H.A.R.R.Y. hat geschrieben:
22 Jun 2021, 16:51
here in this Forum we have got some kind of thread dedicated to pneumatic cylinder lubrication... There you find the lubricant recommended to be Paraffinum perliquidum
Yes, I've read it... I'll read it again. At this point I can say I've browsed the whole forum, my "new posts" list is always clear. My Google Translate is always on for German, so that okay :) Wikipedia shows that Paraffinum perliquidum is mineral oil, which I can buy at the Apotheke (I just love this word).
The old (blue) cylinders lack some sealing gasket on the piston shaft. This is where always the air escapes to ambient ... pfffft.
I'm almost sure the hiss comes from the solenoid valve. The valve is really minuscule, the internal diameter of the inlets is just 1.1 mm and the outlets are 1.8 mm.
Did you check that there is some gap between the levers and the base plate? The hinges also are with leastmnost friction?
Yes, no problems heree. Now I'm experimenting with the cylinders below the base plates. I've taken a stainless steel axe and cut off some material from it so I have something similar to the shaft of the encoder engines. The axle fits in two clip adapter 36227: one below the table, another at the top. This assembly rotates smoothly with very low friction.
The ball mass should be similar to those of ft
The seller answered me, it's around 8.4 g.
With your setup there is minimum to no pressurized air reservoir.
I've tested it with the blue air tank too. The force is certainly higher, but the "pfffft" is also stronger so that the time taken to return is longer... Maybe timing the valves with the Arduino will give optimal results. I'll let you know!

Guys, many thanks for your patience and all the help so far!

Rubem

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

Beitrag von rubem » 22 Jun 2021, 17:45

Hi again!
rubem hat geschrieben:
22 Jun 2021, 17:30
I'm almost sure the hiss comes from the solenoid valve
It is interesting to note that the piston offers some resistance when moving the it back by hand, even if it is simply connected to the valve as shown below and nothing else. The hiss is also there. Interestingly, there is no extra resistance (at least nothing I can notice) when moving it forward.

Cylinder and valve.png
Cylinder and valve.png (72.83 KiB) 317 mal betrachtet

Greetings,

Rubem

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

Beitrag von Harald » 22 Jun 2021, 19:52

The lubricant does not adhere in a way you would like it to. The rubber sealing displaces it and makes direct contact with the cylinder wall. Only during the first millimeters of pushing the piece, you build a layer of lubricant between wall and piston.

Somewhat off topic:
The valves contain a solenoid, which means a coil, which means you are switching an inductive load. There should be
a bypass / free-wheeling diode (Freilaufdiode) in parallel to (each of) your switch(es).

viel Erfolg!
Harald
--- Ich liebe es, wenn ein Modell funktioniert. ---

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

Beitrag von rubem » 22 Jun 2021, 23:33

Hello Harald,

Welcome to the discussion!
Harald hat geschrieben:
22 Jun 2021, 19:52
The lubricant does not adhere in a way you would like it to
At least this confirms my feeling that it lasts only for a while.
The valves contain a solenoid, which means a coil, which means you are switching an inductive load. There should be
a bypass / free-wheeling diode (Freilaufdiode) in parallel to (each of) your switch(es)
Hmmm, yes, I read about it somewhere here in the forum. Since I'll use a DRV8833 motor driver for my next tests, it seems I won't be needing them for now ). But you guessesd right, I'm not using them across the switches :) I'll try to keep that in mind.

Thanks and best greetings,

Rubem

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

Beitrag von rubem » 21 Jul 2021, 16:32

Hello again,

I'm back with a follow-up: I've given up on pneumatics for my pinball project. :o I've replaced the valves and cylinders with push-pull 6V solenoids (model JF-0530B) controlled by a simple Arduino program. The solenoids are very compact (the body measures 30 x 15 x 14 mm, so they fit perfectly in the ft grid), just take a look:

flipper assembly.jpg
flipper assembly.jpg (72.72 KiB) 97 mal betrachtet

After some experiments and several tests, I've decided to go with a power supply taken from an old laptop computer (19.5V, rated at 3.16A). Other power supplies, including one rated at 3.9 A, couldn't stand the two flippers being fired at the same time, they switched off for a couple of seconds. The driver is a good ol' L298N. The advantage is that it's rugged and short-circuit protected. It must be, the coil resistance is just around 5.5 Ω. I've fried a step-up regulator in the process...

The solenoids get full power for 50 ms and then the program drops the PWM duty cycle to about 15% (40 / 255) which is more than enough to hold the flipper up while the button is being pressed. The coils get lightly warm, but that's it. And the initial thrust is more than enough to propel the ball all the way up.

Anyway, the original subject of this thread is kind of lost, hahaha :D I'll create another one when I have more news on the pinball table. Again, many thanks for your ideas so far!

Best regards,

Rubem

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