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DIY servo valves w.i.p

Discussion in 'Pneumatic equipment - outdated' started by egoexpress, Oct 4, 2007.

  1. egoexpress

    egoexpress Active Member

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    Ok, let me see some thoughts how we could realize it. The good thing is, that we wont need to invent electronics, as Tronicgr' servo controller interface would be capable to control the servos.

    We'd just have to invent a mechanism, to translate the servo rotation to the choke.

    The problem that I see until now, ist how to get a multi-turn servo. Are cheap(like RC servos) multi-turn servos availabe anyway?

    I have a 1/8 choke, but it needs 15 rotations to fully open/close. Thats too much.

    Because of that I orderd a 3/8choke for testing puposes.
    [​IMG]
    I hope it will open enough with just a single rotation^^
    If not there are 1/2 ones available as well...

    C'mon guys! Let's see if we are able to improve the pneumatic simulators :)
    Any suggestions, which type of servo could be used for this job?
    Perhaps with a pulley-belt?

    BTW, I've paid just 6Euros including shipping for this choke :)

    ego
  2. Ads Master

    Ads Master

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  3. tronicgr

    tronicgr

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    If you use a standart servo (ok a little bigger to handle the torque) you can remove the end stop limiters (to convert it to a continues rotation and also desolder the existing potetiometer.

    Then you could attach the valve handle to the servo horn somehow.

    Now about the position feedback... You can connect a 10turn potetiometer in place of the 270degrees that the servo uses but not inside the servo, outside with an extension cable.

    Then you can use some gearing to reduce the 15 turns of the valve handle to the 10 turns of the potetiometer. Large gear spur on the valve handle and a little smaller on the potetiometer axis rod.

    This way you can still use the electronics and the motor of the original servo that is easy and cheap to use.

    One thing to consider though. The servo rotation speed will be a little slow! So if the servo can handle the torque you can use gearing spurs to speed up the rotation. Or you can remove the existing servo gearing and replace them to have more RPM output...

    Thanos
  4. SimHawk

    SimHawk Member

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    Good idéa. I will experiment with such a solution as well, but I have to get my HW first and build the frame. Maybe I'll wait a bit with the 5/3 valves and try out a solution like this first.

    Servos used for RC sailboats are high torque and worth a look.

    It is maybe OK to use the valve only 10 turns so that it fits with a standard pot. If that does not give enough speed one can increase the pressure in the system.
  5. tronicgr

    tronicgr

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    Another idea, I just had, is to use a very large spur on the servo horn alligned with a very small spur on the valve handle.

    This way you can elininate the servo hack entirely as the servo will use it own servo potetiometer for the position feedback.

    Again here, the issue of large torque needed arises. Larger servo then?

    @ego, can you tell us what torque is needed to turn the valve handle?

    Thanos
  6. egoexpress

    egoexpress Active Member

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    :idea: servo hack - thats exactly the input I've wanted :)

    Concerning the valves. I rather want to use a bigger valve, than using more than 3 valve rotations.

    I hope the ordered 3/8 valve will let go the same air flow through with 3 rotations as the 1/8 fully open.

    The festo ones are fine threaded :(
  7. SimHawk

    SimHawk Member

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  8. tronicgr

    tronicgr

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    They have solenoids that are current driven. Meaning that to drive them you need a power amplifier that outputs currents up to 1Amp! Not very easy to control with microcontroller directly.
  9. SimHawk

    SimHawk Member

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    You cant drive it directly from the uC, but you need a DAC and a power transistor to drive the coil. Should not be a problem. You need a heatsink on the transistor.
  10. egoexpress

    egoexpress Active Member

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    @Simhawk

    However. Do you you know their price? I think it would make more sense to talk about how to realise cheap servo valves.
  11. SimHawk

    SimHawk Member

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    I have no idea of the price, I just saw that a proportional valve existed and thought that this was maybe the thing we where aiming for. I have very little knowledge of pneumatic equipment so I just got a little bit excited! :D
  12. tronicgr

    tronicgr

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    I examined carefully all the possible conficurations and found out that the most propper way is the one indicated in the picture below:

    [​IMG]


    Its a conbination of the two ideas that I mentioned before, that leaves us with both full rotation speed and full position presision. It should be capable to fully turn on-off the valve fast...!

    The only problem you may encounter is to find proper tooth gears. If you can't find gears with such tooth number, here is the ratio of the gears:

    Servo Gear / Pot gear = 1 / 4
    Servo Gear / Valve gear = 1 / 2.666

    Then, If you have a servo gear with 100 tooth you can calculate the tooth for the potetiometer gear like this: 100 / 4 = 25 tooth
    And the valve gear should be: 100 / 2.666 = 38 tooth (rounded).

    Below you can see how is attached the potetiometer inside a normal servo to see the difference in the method mentioned above:

    [​IMG]


    Regards, Thanos
  13. egoexpress

    egoexpress Active Member

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    @Thanos

    Tanks for the input!

    Btw, the 3/8 valve does not provide an sufficient airflow within 3-5 rotations :(
  14. tronicgr

    tronicgr

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  15. SimHawk

    SimHawk Member

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    Interresting, the price was about 77 Euro. One of these could regulate the airflow into two 5/3 valves, eliminating the need for two of the 5/3 valves used for multi speed.
  16. tronicgr

    tronicgr

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    You will need two of these proportional valves connected to the input of two 5/3 valves to have different speeds on each actuator!

    Each actuator should be connected to a 5/3 valve!

    Its totaly different control from using matrix! But very interesting!!

    If you like to try it I'll support you with electronics and code! :)

    Thanos
  17. SimHawk

    SimHawk Member

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    It is tempting to try. :) One can start out with one proportional valve - same speed on both actuators, just to check the functionality of the valve. I have to finish my tripple speed setup first, still waiting for the valves via snail-mail from US to Norway. I have spent all of my hobby budget on this so I have to wait for further income on my hobby account. :wink:
  18. egoexpress

    egoexpress Active Member

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    Their price is very affordable!
  19. egoexpress

    egoexpress Active Member

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    I'd like to buy two valves from Clippard for testing purposes.

    If they are as good as they seem, we dont need to build valves by ourselves anymore, if their valves just cost 77Euro^^

    They have plenty models with weird units in their catalog.

    http://www.clippard.com/downloads/gener ... _%20MB.pdf
    Search for proportional in the pdf-reader.

    Dont know which of these valves are universal, or if they just fit on their own valves.

    Could you please help me to choose the right options?

    Thanks
    ego
  20. SimHawk

    SimHawk Member

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    Is the airflow sufficient? The highest i find is about 22 ltr/min. I am not sure how much flow we need for the sims.
  21. tronicgr

    tronicgr

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    And before that we need to consider the DAC electronics needed to drive it, as it inputs current to go to the desired proportional position!

    And DAC electronics need a voltage output from the microcontroller meaning we cannot use the simple R/C servo outputs. Instead, we need PWM signals to create the voltage output from the microcontroller.

    I must do a little more research on the connection ways a little. Don't buy something that we could not interface easily later...

    Regards, Thanos