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ArchitecturalModel Dilemma..

Discussion in 'General Electronics Discussion' started by ConnorP, Sep 19, 2013.

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  1. ConnorP

    ConnorP

    1
    0
    Sep 19, 2013
    Hi,

    I'm building an architectural model for one of my final year projects at uni, and i'm having trouble designing the operating circuit for it.

    The model is of what is commonly known as 'The Sliding House' by drMM architects (give it a google and you'll see what I mean about the motor) and it is in 1:40 scale, which puts it at about 80cm unextended.

    I'm a complete novice in electronics, although I'm having basic lessons from one of the pro Modelmakers at the company I'm doing work experience in, so I have a (very) basic grasp of it as of yet.

    I'll explain what I'm trying to do first and hopefully one of you would be kind enough to teach me how such a system would operate if you could?

    Ok, so I need to plug the model into the mains, just so you know where my power is coming from initially. (I know about fusing and transformers to convert so I'm ok up the the converted side of the transformer)

    Ideally, due to aesthetics and ease of demonstration, I'd like to use a 3 position rocker switch (on-off-on) to control the direction of the motor. Unless there are any better suggestions of low visual impact switches that would suit better? Also, i'd like the switch to only have to be depressed for a second (not held down) but the model to move until it reaches either end of the rack.

    I need to run a DC motor with low RPM to control a rack and pinion system, the rack being attached to the bottom surface of the outer part of the house, and the pinion being attached to the shaft of the motor to drive it.

    I need to reverse the polarity of the motor when the switch is presses from either left or right to move the model left or right (sorry if this is obvious, just trying to include as much info as possible.

    At both ends of the rack, I plan to install microswitches (have no idea what contact config) so that when the piece reaches the switch it stops the circuit and the model isn't working against itself, I believe this type of system is often found in model railways, although I want the piece to stop when it gets there.

    Hopefully this is clear as of yet, sorry if I'm getting anyone confused! I actually saw an image of a circuit similar with a blue train and microswitches which looks kind of what i'm after, without the constant movement. That guy got loads of help so hopefully I'll get the same!

    Ok, so here comes the hard part. The model has a 3rd position, the middle. It's important it stop at the right place as windows line up etc and it would ruin the effect if it wasn't precise. This is the part I'm really stuck on, I don't know if I need another micro switch in the middle (maybe a lever microswitch switch that gets depressed by a lump on the bottom of the moving piece that contacts it at the right position?), and even then I wouldn't have a clue how to wire it so it works from both directions.

    So, positions A, B and C. In terms of switch operation I'd love it if there was a way to have a 3 position switch, the middle position being no movement, and each momentary touch of a direction to send the model the appropriate direction. So imagine we are in position A, one touch of the right hand side of the switch would see the model move slowly right into position B, and another touch seeing it move into position C. A touch on the left side of the switch would see it move back into B, and so on.

    I know its long winded and fussy and everything, but I just have a vision of the movement in my head and I know with enough research and time (and grovelling) the solution is out there.

    Thanks in advance for the bundles of expert advice i'm about to receive, it's appreciated

    Cheers
     
  2. Fish4Fun

    Fish4Fun So long, and Thanks for all the Fish!

    464
    105
    Aug 27, 2013
    First thing to do is express in Boolean logic what your movements are. From there you can use either discrete logic or a microcontroller to control the movement. As this is a school project with an implied completion date, you should carefully consider your skills prior to committing to any particular path. Personally I would use a stepper motor and a lead screw in combination with a microcontroller, but if you are not familiar with microcontrollers the learning curve might require more time than you have.

    A simple solution using a stepper motor and discrete logic is quite possible. A simple solution using a DC motor, limit switches and discrete logic is possible. A silly-simple solution is possible using a brushed DC motor, a three-way switch, perhaps a DPDT relay and limit switches.

    As this is a school project, I think you should decide how you want to proceed, and work on the solution until you reach an impasse. I for one will certainly not solve the problem for you, but I will happily help with any particular step in the process. Again, I would urge you to define mathematically your desired motions, from there it is simply a matter of replacing logic statements with their electronic counter parts.

    Fish
     
  3. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    Here is a simple relay circuit that may fulfil your needs; if there is something wrong with the design, I just can't see it. Note that I have shown the rocker switch as pushbuttons operating DPDT relays. It would also be possible to fabricate a lever operating two DPDT pushbutton switches instead. The latching relays need to have Form-C contacts (break before make) to avoid shorting the power supply.

    [​IMG]
     

    Attached Files:

  4. Fish4Fun

    Fish4Fun So long, and Thanks for all the Fish!

    464
    105
    Aug 27, 2013
    @==> Laplace hehe, you didn't label the center limit switch for him, how will he get his A? To be honest I have stared @ the schematic for ~10min and my ADD/ADHD has gone into overdrive (I want to put it together to make sure), but I believe your schematic meets all of the assignment criteria.....ok 10 min later, perhaps a small glitch.....The design criteria have it "running to center and stopping", If either of the bottom relays is engaged then the ground path for the top relays is controlled by either of the two bottom relays and the center limit switch is a parallel ground path, making it moot. You would need to make the ground path to the top relays a series connection with the limit switch, and then you would need to add a momentary switch to "get past the limit switch". Or maybe my ADD/ADHD has taken me over the edge?

    I had a similar project years ago involving a measuring system. The design criteria was that an operator push a button and a weight drop down until it reached "bottom" then the weight should automatically return to home. Of course there was an encoder and LCD display. I managed it with 1 * DPDT, 1 * SPST, + 2 limit switches and a MosFet.. Sadly it took me days to work out the logic. Figuring out the physics to make the limit switches behave properly took weeks. Making it all work on the end of a 40ft feed boom took months, lol.

    Fish
     
  5. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    Regarding the parallel path to ground, instead of a 'glitch' try to think of it as a 'feature'. Since the center limit switch breaks the ground connection at the center position, the house would sit in the center forever unless a brief ground contact is provided to 'kick' the house off center when someone activates the left/right control switch. Also, the house can pass through the center position without stopping if the control switch is activated at that point, otherwise the center limit switch will cause the house to stop in the center.

    Of course, the wiring could be vastly simplified by using a micro-controller chip and MOSFET H-bridge switch but it seemed that such sophisticated electronics were uncalled for. I won't even claim that this is an optimized solution, my purpose being to show what could be done with a few relays.
     
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