elevator system using relays

Discussion in 'The Projects Forum' started by theanih, Oct 10, 2010.

  1. theanih

    Thread Starter New Member

    Oct 3, 2010
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    0
    i've read almost all the threads in AAC about elevators and dumbwaiters, and some threads helps but some just makes me more confused. so i would like some help from you guys who seems to know a lot in this field of expertise.

    i'm building a model of a 3 level elevator using relays but the designing of the systems needed to control the movement of the cart is really confusing even after i managed to build the block diagram.
    there are a few questions i'd like you guys to answer;

    - i'm using a dc motor, so how can i make it go reverse and forward?
    - how can the motor knows when to stop at certain levels?
    - how can i make the cart to stop at level 2 then continues on its way to another level (for example; the cart is at level 3, someone pushed the button on level 2 and 1, so the cart should first stop at level 2 and continues to level 1)?
     
  2. ke5nnt

    Active Member

    Mar 1, 2009
    384
    15
    I'm thinking the best way that I would know how is using a microcontroller to control relays based on your button pushes. DC motors usually will go in reverse when reverse polarity is applied to them, you should be able to get up and down movement by changing polarity.

    Not sure if you're familiar with microcontrollers but if it were my project, here's what I would do (in a nutshell).

    My lift would have a light to voltage diode on it (a diode that generates a voltage when light is applied to it. Each level the lift would stop on would have a LED lined up where the light to voltage diode would pass by. Now when you press a button, the microcontroller (MCU) trips a relay that would start the lift in motion, and the LED for your selected level would illuminate. The MCU would then scan the light to voltage diode for a voltage to set that MCU pin high. When the lift passes the level that is selected, the LED would beam light into the diode and generate a voltage which would set the pin to high, which would tell the lift to stop moving.

    You could also use the LEDs and light to voltage diode to determine which level the lift is currently on. Say the lift is on level 2 and you select level 1. First, the level 1 LED is turned on and the diode tested for voltage, no voltage is seen so the MCU knows the lift isn't on level 1. Then the level 2 LED is turned on and the diode tested for voltage. It sees a voltage so it then turns on the appropriate pins to move the lift down instead of up.

    Not sure how real elevators function. Without knowing more about electronics than I actually do, if I was in your position, I'm just saying that's what I'd do. Only putting forward this suggestion because no one else has responded to you.
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,094
    3,033
    I'm sure I would be bewildered too, just like if I had to design an automatic transmission or myriad other things we take for granted. But I also know such things have already been in wide use for, oh, what, 100 years? Maybe a quick trip to the elevator closet of an old building would be a good investment of your time. Don't reinvent wheels.
     
  4. theanih

    Thread Starter New Member

    Oct 3, 2010
    21
    0
    fyi, i'm in the middle of nowhere with buses as the only transportation and parts are really really limited here. there's only several electronics store and etc but lots of hardware stores. this morning i went out and nope, there's no MCU available. i have access to an omron plc module but unfortunately i have no software to write the ladder diagram and download into the module. hence, the relays.

    but anyway thanks for the suggestion.
     
  5. n1ist

    Active Member

    Mar 8, 2009
    171
    16
    I'd use two form-C (SPDT) relays to connect either side of the motor to V+ or GND. Or use a dual form-c wired as a reversing (crossover) switch and a form A (SPST) to turn the motor on and off.

    Have the car press microswitches when it is level with each floor. These can open the motor power to stop the car. Wire relays in parallel with the switches to allow the car to resume motion

    This is where you get to make a state machine out of relays. The microswitch for floor 2 would stop the car and start a delay. When the delay expires and floor 1 has been pressed, a relay can short out the microswitch for floor 2 to allow the car to continue down. To make things a bit more realistic, have the push buttons pull in a latching relay (or latching relay circuit) and have the appropriate floor microswitch reset the latch.

    /mike
     
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  6. wayneh

    Expert

    Sep 9, 2010
    12,094
    3,033
    Sorry if I sounded condescending - I didn't intend that. I'm merely suggesting that your time might be efficiently spent learning from the hard lessons of designers before you that have solved these problems.

    If I have seen further it is only by standing on the shoulders of giants. - Isaac Newton
     
  7. ke5nnt

    Active Member

    Mar 1, 2009
    384
    15
    Oooh! I forgot about microswitches! Great idea. I'm not that familiar with the availability of relays since I've not used them much up to this point, but a SPDT relay sounds like a winner. Great suggestions.
     
  8. theanih

    Thread Starter New Member

    Oct 3, 2010
    21
    0
    thanks for all the help. i've just finished the elevator and it will be up and running after a few finishing touches.
    thanks again.
     
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