DC Motor to control hot/cold shower valves

Discussion in 'Homework Help' started by Connord0902, Dec 9, 2017.

  1. Connord0902

    Thread Starter New Member

    Dec 9, 2017
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    Background: For our senior design project, we are creating a "smart bathroom" where we are trying to make all of the systems hands-for (selling it for sanitary purposes) and I am responsible for the shower portion (we are also working on a smart mirror and a smart toilet). This includes a smart hub with a Raspberry Pi that will control all of the systems via voice command (e.g. "Turn the shower on", raspberry pi sends a signal to DC motors attached to 3D printed shower handles and turns them to proper temperature settings (70% hot and 30% cold would be a 270 degree turn on the hot handle and a 45 degree turn on the cold handle)). To regulate the temperature, we are going to utilize a thermistor circuit at the output of the shower head (e.g. If the temperature is above 110 degrees, the raspberry pi will tell the DC motors to turn all the way off to turn the water flow off and prevent scalding). We are using a shower with two handles (one hot, one cold) and I am going to remove the original handles and attach 3D printed handles that I will make in SolidWorks. I then plan on attaching the DC motors to the top of these plastic handles so that they can be moved/adjusted autonomously.

    My Question: I have never worked with DC motors and don't really know what I would need. A lot of the motors that I'm seeing seem to represent RPMs as a selling point, but I don't think the DC motor that I need will need to turn fast, or much at all. I figured the DC motor would need to be very precise, so that incremental changes can be made to adjust the temperature (e.g. the water reads 95 degrees, but the user wants it to be 100 degrees, so the raspberry pi tells the hot water DC motor to turn 10 degrees to allow more hot water to flow). I'm assuming this would be similar to the motors used in robotic arms, where small, precise movements are necessary?

    Any help/insight/feedback would be greatly appreciated!!

    Let me know if I need to clarify anything.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Servo motor, DC and the like require some kind of feedback element for positioning, you may want to look at stepper motors, these require no feedback,
    Also at the RPM you would need, gearing would be advisable.
    And of course they would need to be TENV (totally enclosed, non ventilated).
    You can also get motorized valves.
    Max.
     
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  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Welcome to AAC!
    The motor would need to be a 'gearmotor', i.e. one with a high reduction ratio gearbox attached so that its output shaft rotates slowly but provides high torque. You would also need a 'shaft-angle-sensor' attached to the valve/tap to sense its position. Do a bit of googling to research those.
    Off-the-shelf electrically-controlled proportional mixing valves are available, but they are very expensive for a student project!
     
  4. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    I've successfully done valve designs in the past using an ordinary dc gearmotor actuating an ordinary ball valve, but with the valve's shaft (or the gearmotor's output shaft) monitored using an absolute magnetic on a chip, such as the AS5045. With it, I obtained extremely accurate positioning feedback at a very low cost.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I wonder if they use that IC in this?
    ENI-1024.
    Max.
     
  6. Connord0902

    Thread Starter New Member

    Dec 9, 2017
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  7. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    Maybe they do... look at the pic on page 6 of this document. But I see an additional chip there that might be used for buffering the output, and convert it to a push-pull type.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I believe that is a RS485 differential driver.
    Also it is a little misleading, usually the natural pulse count is given before x4 etc, but they state 1024 which means a natural count of 256!
    Max.
     
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  9. Connord0902

    Thread Starter New Member

    Dec 9, 2017
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    Just joined this forum and I'm astonished at the quick responses and the insight you all have provided!! Much appreciated.

    With that being said, I'm looking into each of the topics you all suggested and I will follow up with questions when/if they arise.

    Thanks again.
     
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  10. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    Silly me... of course it must be a differential driver! ... and btw, thanks for suggesting using the AM26LS31/32 differential drivers/receiver to help extend an encoder's output in a previous circuit of mine. I've been using it for almost a year in one of my machines and it's been working flawlessly!
     
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