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Hi,

I need to build a device that opens a chicken coop door.

The idea is quite simple, a motor connected to an axle that pulls a string up just like a wench. It would be activated by a relay timer setting it to open at 2 different times of the day (Morning and night) for a specific amount of time, enough to open and close the door. The problem I'm having is how to make it close...

I have a 6v electric motor that works just fine for the job and inverting the polarities can also close it, but I wanted to make the polarities automatically invert somehow, after each activation, in the morning it open, and inverts the polarities making it close at night and so on. I could attach a string to the door and use a polarity inversion switch, the string pull the switch when stretched enough, but that seems way too trashy haha. Having a linear actuator is not an option where I live, and I thought about using a spring to close, but I don't want to make a possible guillotine.

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  • $\begingroup$ adafruit.com make inexpensive SBC single board computers (Gemma M0, Trinket M0, Feather (variants)) and motor controllers (just dig around their website). A light sensor could be the trigger for daybreak, or a RTC real time clock could be another add on board. You'll have to program what you want, but it is a fun learning experience. arduino.cc started with the UNO (and earlier variants), but adafruit has the bells and whistles. $\endgroup$
    – Jim Clark
    Jul 23 at 14:06
  • $\begingroup$ Won't you be making a motor-driven guillotine? What do you plan as sensors to check for obstructions to stop or even reverse the motor? Why not check out some of the window control circuits used on cars? $\endgroup$
    – Solar Mike
    Jul 23 at 14:14
  • $\begingroup$ @JimClark Since from the answers here the simpler option is using H-Bridge it will actually be cheaper to use a light sensor than using a rele timer, and I won't have to bother about daylight saving time. Thx $\endgroup$
    – Renan
    Jul 23 at 17:15
  • $\begingroup$ @SolarMike Not really, since the door will close very slowly it will give more than enough time for the chickens to make a decision, if they don't...well we having chicken for dinner I guess. $\endgroup$
    – Renan
    Jul 23 at 17:16
  • $\begingroup$ Define how cheap you need to be a prigrammable biard with a h bridge can be done at about 4 euros/ 5 dollars but that depends on the motor $\endgroup$
    – joojaa
    Jul 23 at 20:09
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If I am not mistaken, you can use an H-Bridge for that.

If you are using an arduino for example, there are a few motor drivers like L298N which do exactly that job (control the direction and speed of a dc motor).

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  • $\begingroup$ +1 for supplying an actual link. $\endgroup$
    – Eric S
    Jul 23 at 14:33
  • $\begingroup$ That seems to be the best option indeed, I was trying to stay out of Arduino because of the price of it in Brazil but in the end, it will be a much more reliable and good learning experience. Thx for the link btw, very handy. $\endgroup$
    – Renan
    Jul 23 at 17:20
  • $\begingroup$ You don't need to use arduino. You can use only the board with the power supply and you only need to provide digital signals to control the motor $\endgroup$
    – NMech
    Jul 23 at 19:48
  • $\begingroup$ @Renan any microcontroller will do. Arduinos are expensive yes but you can get a microcontroller for 5cents (only the programmer is hard to come by) $\endgroup$
    – joojaa
    Jul 23 at 20:11
  • $\begingroup$ @renan joojaa has a valid point. The details of the motor you will use are very important. You need to check the voltage and the current requirements for nominal operation Of course if you use a gear box that can also play a role. $\endgroup$
    – NMech
    Jul 24 at 9:01
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An alternative to an H-Bridge (preferred method if you are already using a controller - it also lets you use those overkill relays for other projects) would be having +/-6V at the motor. This would mean a 12V supply with one leg of the motor at a regulated 6V. You connect the second leg to 12V for one direction and 0V for the other direction, getting you 6 V and -6V over the motor respectively. Probably about the the same cost as h bridge over the existing 6V though.

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  • $\begingroup$ That does sound like a possible option, any examples of something like that being used? I do get the concept but I'm pretty ignorant when it comes to circuits. Thx $\endgroup$
    – Renan
    Jul 23 at 17:22
  • $\begingroup$ Letting us know more about what the motor is and how much current it requires will help. Although very popular the L298N will not support very much current plus it has a large voltage drop when it has a load. Can you get two signals (open close) out of your controller, that would make the solution much easier. Another option is a inexpensive sprinkler controller that has 2 or more zones then you get your open and close signals. $\endgroup$
    – Gil
    Jul 24 at 1:48
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You can do this with a pair of Omron programmable timer modules that mount onto DIN rails, no software required. They are extremely flexible and can be easily configured to perform a variety of tasks like this. They are basically a set of relay contacts which are exercised by an internal clock, packaged into a small plastic enclosure with a clock display and a couple of system status LED's on the front panel.

New, they cost 150 dollars each but can be found for 25 to 30 dollars each used in industrial surplus outlets or ebay. In a previous lifetime I built sequencing controllers for semiautomatic production line tools out of Omrons with great success- no arduinos or raspberry pi's needed.

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Make a crank axle to lift and lower the coop door without having to reverse the motor. A full cycle would entail: start, stop, start, stop. Motor on-time for each start run is all that is needed.enter image description here

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