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Pnuematic Actuation — Parallax Forums

Pnuematic Actuation

Naphtali MooreNaphtali Moore Posts: 42
edited 2007-10-19 10:36 in Robotics
Ok, so I want to use Pnumatics in an audio animatronic. BUT I'm having a hard time finding any good tutorials. Do you guys have any suggestion? I figured out the air supply, bought several small rams/ cylinders. Now to figure out position recognition and speed control. I was thinking of attaching a servo to each joint and using it to report the position. Well thanks for any feed back! [noparse]:)[/noparse]

Comments

  • Bruce BatesBruce Bates Posts: 3,045
    edited 2007-10-16 09:16
    Napthali -

    If by "servo" you mean an R/C servo, that would indicate an output device. How were you planning to use it as an input device to figure out position?

    Moreover, unless you are planing an involved pneumatics sytem with proportional controls, a pneumatic cylinder is usually either actuated or not, extended or not - call it what you may. You ought to know whether you've actuated it or not, so position information is quite superfluous, unless of course you are speaking of a proportional system. If it IS proportional, you might choose to use multiple rotary and/or linear potentiometers to determine the actual positions. I'd imagine multiple encoders would be a bit expensive.

    Regards,

    Bruce Bates

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  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2007-10-16 12:18
    Regarding rotation, using a passive component, such as a potentiometer, will greatly reduce cost. But if you need a high degree of acuracacy, a rotary encoder is likely to be more useful than a servo.

    But it sound like it more a matter of determining position. In that case, microswitches are easily available.

    Speed is controlled by how quickly the valve is opened or closed. In some ways, pneumatics can be difficult to control unless you find a good way to reduce the overall pressure.

    I think that the problem with finding tutorials is related to the fact there are so many options and choices of a mechanical nature. It is difficult to write a useful text when so many mechanical choices are available. The movie industry uses this technology, but the individuals that make displays consider them to be 'trade secrets'.

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    "Everything in the world is purchased by labour; and our passions are the only causes of labor." -- David·Hume (1711-76)········
    ···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
  • kelvin jameskelvin james Posts: 531
    edited 2007-10-17 05:26
    The easiest way to get pneumatic speed control is to use an electronic proportional valve, but they are a little expensive, around $50 a pop. Check out Clippard.com for miniature valves. They might be had cheaper elsewhere, like surplus or ebay.

    www.clippard.com/store/byo_electronic/byo_proportional_valves.asp
  • Naphtali MooreNaphtali Moore Posts: 42
    edited 2007-10-17 06:28
    RC Type Servos and postion reporting:
    The Parallax Servo Controller allows for position reporting of any attached servo; whether on the move or stationary. So if I attached one of these to a joint then I can call it and get the position. I already have a servo controller, 10 standard servos, 4 micro servos and 2 continuous servos. So the cost of using servos would be slight. (Check ebay for servos, I got 10 for $50)

    Basicly, I'm looking to save data for a show in time stamps like this

    1232 Servo1 15, 2 = [noparse][[/noparse]time stamp in millisecs] <ServoName> [noparse][[/noparse]position], [noparse][[/noparse]speed]
    1234 Servo2 130, 10
    etc . . .

    So e.g. I want to use a cylinder to move an arm to a range of positions at a range of speeds. I guess that means I want I proportional system. I know it can be done with pneumatics, I've seen it. Oh, Kelvin, I checked out the proportional valves you suggested. Thanks for the link! I might just have to pick one of those up next pay check.

    Now can any one tell me the difference between a single and a double acting cylinder. I have ordered a couple of each with which to experiment. And whats the difference between 2-way, 3-way and 4-way solenoids?
  • kelvin jameskelvin james Posts: 531
    edited 2007-10-17 17:13
    Got this off the Clippard site, should answer some questions.
    pdf
    pdf
    Intro_to_Pneumatics.pdf
    722K
  • D FaustD Faust Posts: 608
    edited 2007-10-17 18:54
    The PSC cannot tell you the position of a servo, but the last pulse it sent to it.· If you send a pulse to the PSC tellign the servo to turn right and hold the servo so it can't move, the PSC will tell you that the servo is all the way to the right.

    Just use a pot.· That is how a servo determines where to move anyway.

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    --DFaust
  • Naphtali MooreNaphtali Moore Posts: 42
    edited 2007-10-19 10:36
    Dang! My wife just got laid off. That means; no buying new parts till she settles into a new job. And my new cylinders will be arriving any day now. I still need at least 2 electronic pressure regulators, 2 2-way valves and 1 4-way valve.

    I have found some cylinders with built in position reporting devices, but the added cost is much greater than a pot. Also the cylinders will be attached indirectly to the armature by means of some sort of spring to allow for shock absorbtion and more natural movements. So the cylinder position will not always accurately reflect the armature position.

    Well looks like I get to play with the servos for now. [noparse]:)[/noparse]
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