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Auto/Motor Need help choosing the necessary motor for my first ever DIY project

  1. Aug 12, 2018 #1

    I have decided that no matter how many times I ask, people will always leave my bedroom door open. Therefore, I have decided to try my hand at a DYI project to create an automatic door closer. I'm aware these already exist but I'm also doing this because I've always been interested in robotics and figured this would be a fun way to get my foot in the door.

    The main things that I am struggling with is deciding how much voltage my motor will need, and what type of motion my motor will need to use. My door weights about 60 pounds and the motor will only need enough force to close it close it shut. I do not need it to open the door. How can I calculate this? Will the angle in which the door is open affect the power needed?
    Last edited by a moderator: Aug 14, 2018
  2. jcsd
  3. Aug 12, 2018 #2


    Staff: Mentor

    Welcome to PF.

    You will need some clever mechanical design not just motor design. The angle changes very much and that's important. You also need a way to stop the motor when fully closed, and a way to sense when it should turn on.

    I suggest that you start by studying the pictures of the very many existing electric door closer. This search in google images will show you many.
  4. Aug 13, 2018 #3


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    I would suggest a cheap alternative, but it might be too subtle. I'd look at adjustable spring hinges. If there were three on a well hung door, they will probably close it, or at least pull it very close to latched. I usually put one on doors that aren't level and want to stay open if I can't level the door any other way.


    If you install a motor to close a door, there should be some kind of safety or torque limit that prevents the door from closing on a person, pet, etc...
  5. Aug 14, 2018 #4


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    The max force required is likely to occur when compressing the latch. Perhaps measure that
  6. Aug 14, 2018 #5
    I would just try to adapt a tray servo from a CD drive. That is made with slipping allowed, is slow, has some push but not much, also there are the endpoint switches ready...
  7. Aug 20, 2018 #6

    jim hardy

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    It's natural to look to electronics for everything these days.

    as @anorlunda suggested this is more of a mechanical challenge than electrical.
    you're after rotary motion for the door. A mechanical knee action with a couple of rotary bearings could work by gravity.

    If you really want it to be electric i would go to a junkyard and get a couple of automobile window regulator mechanisms for a start..

  8. Aug 20, 2018 #7


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    Or just fit self closing hinges. Lots of versions exist. Not all lift the door like these...

  9. Aug 25, 2018 #8
    I'll also suggest you go for a simple & quick solution like self-closing hinges shown above.
    But if you really want to get this done electrically, I'll recommend a detection method using magnetic switches:


    embedd or stick a magnet in/on your door in a way that when the door closes, the magnet will lay directly beside the switch, which will complete whatever circuit the switch is connected to. The connection will break as soon as the magnet leave the switch(when you open the door)

    Hope this helped you in some way.
  10. Aug 26, 2018 #9


    Simple lift or spring closures are OK, but the devices pictured above allow the door to close slowly, in a damped fashion, until the last few degrees where they release the damping. This slams the door slightly so the latch can engage. Otherwise your door will end up ajar, resting on the latch.

    A motorised door would have to be quite torquey to swing the door from that position, would have to shut off in an overcurrent situation (someone standing in the door way, holding it open) and would be quite hard to mount elegantly.

    A car window motor might be suitable.
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