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control a exhaust vent with servo, stepper, or other — Parallax Forums

control a exhaust vent with servo, stepper, or other

jaspittmanjaspittman Posts: 22
edited 2007-07-25 01:39 in BASIC Stamp
I would like to control a exhaust vent with a bs2. I’d like the bs2 to monitor the pressure of the exhaust and open the valve accordingly. I have found a product that can control the vent with a small geared dc motor, but it is manually controlled by a push button. Is there a way to monitor the position on this type of vent? Should I switch to a servo or stepper? Is there a servo or stepper that can withstand temps of about 300 F?

Comments

  • D FaustD Faust Posts: 608
    edited 2007-07-24 18:26
    If you mechanically connect a potentiometer to the vent then you will have feed back of the vent's position. Basically, this is what a servo does (monitor the pot to ajust its position) I'm not sure if a servo could stand up to that heat so you are probably best usign your (specialized?) motor. My guess would be that you could de-wire the button and put in a transitor instead to allow stamp control. Hope this helps.

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    D Faust
  • jaspittmanjaspittman Posts: 22
    edited 2007-07-24 18:35
    do they make high temp pots. can i get one that will fit around the drive shaft of the motor. also i am wondering if i can't take the guts out of servo and us it to drive the dc gearmotor like a servo.
  • allanlane5allanlane5 Posts: 3,815
    edited 2007-07-24 19:24
    Probably not. The DC gearmotor probably has more torque, and requires more current, than the servo motor. Thus the servo electronics might not be up to driving it, and could burn out.

    You could do this with a couple of micro-switches at both extents of the vent position -- one at fully open, one at fully closed. And I assume the speed of movement will be pretty consistent. So move the vent to fully open, then close it for 2 seconds (or whatever) to get half closed.

    You could replace the button with a relay-closure. Or even parallel the button with a relay closure.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2007-07-24 21:21
    If you're using pressure as the feedback variable, you probably don't even need to know what position the vent is in — just that it needs to be moved one way or the other.

    -Phil
  • jaspittmanjaspittman Posts: 22
    edited 2007-07-24 22:47
    "If you're using pressure as the feedback variable, you probably don't even need to know what position the vent is in — just that it needs to be moved one way or the other."

    thats true but i do need to know if the butterfly valve is fully open or fully close so i bon't burn out the motor.
  • D FaustD Faust Posts: 608
    edited 2007-07-25 01:39
    There is a thread that talks about driving a motor with servo guts (this is really just to make a motor driver (direction and speed control), but if you would like the link speak up) , but you still would have to find a way to connect the pot to the motor output. I'm not really sure about high-temp pots, but they are probably more common (if they exist) than high-temp servos.

    As for what PhiPi said, if the pressure was low you could assume the vent to open, and if the pressure was above a certain point you could assume the valve to be closed.

    I think that the microswitch idea would work the best especially in combination with PhiPi's logic. (if you could fit the switches in somewhere)

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    D Faust
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