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Thread: reversable motor for monitor?

  1. #141
    Maximum Bitrate more mods's Avatar
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    I would like to officially thank all those who have participated, contributed, viewed, read, noticed, ignored, or otherwise acknowledge the existence of this thread and or any part of said thread there in. I would especially like to thank those who live, visit, drive through, fly over or otherwise acknowledge the existence of the state of Georgia and its residents there in. Not to exclude others who are not here in Atlanta, but more to pay a special tribute to said Georgians, and others around the world (but mostly here in Georgia). I would also like to acknowledge the vast accumulated knowledge of all the fine people who have participated, contributed, viewed, read, noticed, ignored, or otherwise acknowledge the existence of this thread and or any part of said thread there in, especially those who live, visit, drive through, fly over or otherwise acknowledge the existence of the state of Georgia and its residents there in, but not to exclude others from around the world (but mostly those who live here in Georgia).

    And now for something completely different!

    Ricky, when you said “Right…..” Monty Python popped into my head (I love Monty Python) and this was the result.
    It's the cake having/eating thing.

  2. #142
    Newbie mm_202's Avatar
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    Quote Originally Posted by more mods
    I thought about a servo or stepper also, but then I have to have a controller, because they need PWM. I'm not sure how to set all that up, it would also add a good bit of cost to my project.
    more_mods,

    I would highly suggest going with the servos. Even though they are PWM, they are very easy to setup using just one 555 timer IC. You could build your entire circuit with just the 555 and two transistors (plus supporting components, of course).

    On the other hand, if you wanted to use a DC motor (not sure about the advantages...), then I would suggest using a H-Bridge, not only would you be able to control polarity, but also speed. But if you use the DC motor then you would also need to setup stop points for the motor, its not that much more complex, but why bother if the servos can take care of it for you.

    Let me know which one you are interested in and I'll draw up a quick schematic for you.

  3. #143
    Maximum Bitrate more mods's Avatar
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    Quote Originally Posted by mm_202
    more_mods,

    I would highly suggest going with the servos. Even though they are PWM, they are very easy to setup using just one 555 timer IC. You could build your entire circuit with just the 555 and two transistors (plus supporting components, of course).

    On the other hand, if you wanted to use a DC motor (not sure about the advantages...), then I would suggest using a H-Bridge, not only would you be able to control polarity, but also speed. But if you use the DC motor then you would also need to setup stop points for the motor, its not that much more complex, but why bother if the servos can take care of it for you.

    Let me know which one you are interested in and I'll draw up a quick schematic for you.
    I am interested in the H bridge. How do you control speed with it?
    I am pretty sure I will need to slow my motor down some.
    It's the cake having/eating thing.

  4. #144
    Newbie mm_202's Avatar
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    Quote Originally Posted by more mods
    I am interested in the H bridge. How do you control speed with it?
    I am pretty sure I will need to slow my motor down some.
    I didn't bother reading all of the previous posts (actually I didn't even notice the other 9 pages till after posting), but I saw a schematic of a H-Bridge here somewhere, so at least you'll know what I'm talking about:

    To control the speed of the motor using the H-Bridge, just PWM the signal to the transistors. But when doing that, make sure you are using MOSFETs, not standard transistors, otherwise everything will get *very* hot.

    The PWM for the HB is the same as for the servo, just a 555 pulse train.

    I take it that your not considering using servos anymore?

  5. #145
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    Quote Originally Posted by mm_202
    I didn't bother reading all of the previous posts (actually I didn't even notice the other 9 pages till after posting), but I saw a schematic of a H-Bridge here somewhere, so at least you'll know what I'm talking about:

    To control the speed of the motor using the H-Bridge, just PWM the signal to the transistors. But when doing that, make sure you are using MOSFETs, not standard transistors, otherwise everything will get *very* hot.

    The PWM for the HB is the same as for the servo, just a 555 pulse train.

    I take it that your not considering using servos anymore?
    This project has changed a lot from what it started out as. I have the motor already, the PIC and the Programmer are on the way and Mike and Ricky have put a lot of work into this design. While its not set in stone I dont want to go off in a completly new direction.

    Could you take Mike's design and make the changes you think it needs, ie H bridge and mosfets and any thing else.
    It's the cake having/eating thing.

  6. #146
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    mm_202 makes a good point about heat. MoreMods (now I know where you got your name... ) how much current does your existing motor draw steady state (ie, not at startup, but after running for a couple of seconds)?? The transistors will have a much larger voltage drop across them than MOSFETs would when turned on. Depending upon the current drawn by the motor, this could present a "challenge" for heat dissipation.

    mm_202...since you offered, I would like to see a servo design. I'm not really a motor control guys, so I'd like to see the difference between servos and DC motors.

    PWM could actually be done in firmware in the PIC for speed control of the DC motor. However, I would be a bit surprised if speed control will really be needed for this simple open/close function. Perhaps if the limit switches are really sloppy, you may want to slow the thing down before it reaches the end points. But I would opt for better limit switches with a bit of mechanical "adjustability".

    My 2cents.
    MikeH

  7. #147
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    Quote Originally Posted by MikeH
    mm_202 makes a good point about heat. MoreMods (now I know where you got your name... ) how much current does your existing motor draw steady state (ie, not at startup, but after running for a couple of seconds)?? The transistors will have a much larger voltage drop across them than MOSFETs would when turned on. Depending upon the current drawn by the motor, this could present a "challenge" for heat dissipation.

    mm_202...since you offered, I would like to see a servo design. I'm not really a motor control guys, so I'd like to see the difference between servos and DC motors.

    PWM could actually be done in firmware in the PIC for speed control of the DC motor. However, I would be a bit surprised if speed control will really be needed for this simple open/close function. Perhaps if the limit switches are really sloppy, you may want to slow the thing down before it reaches the end points. But I would opt for better limit switches with a bit of mechanical "adjustability".

    My 2cents.
    One of the reasons I shy away from servos is that I really dont understand them enough.

    I was just writing up this big complicated question about how steppers work and I think in formulating the question I found the answer!

    Servos are just steppers....right!

    See if I understand this correctly.
    • The PIC would feed a steady stream of pulses to the servo at all times.
    • The rate (speed) of the pulse tells the servo where it should be. Even if I pushed the monitor all the way back with my hand it would return to where it was.


    Question is can it get out of time?
    If the monitor was 3/4 open and the power was removed from the PIC, when power was returned to the PIC would it try to move from a full closed position to full open when its already 3/4 open?

    Mike as for my name, and sig. I think they are both true.
    It's the cake having/eating thing.

  8. #148
    Variable Bitrate brooksware2000's Avatar
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    servos are not steppers and are easier to control than the h-bridge design that you are using. In fact, you can control the servos like you would control the motors using the h-bridge circuit. Servos are more precise in that you can send a particular pulse to say, have the servo go to the far right, far left, or center. I believe it would be a lot easier than the h-bridge and you could control the servos right from your PIC.

    Example code in basic for pics:

    pulsout 1, 127

    would send a command to a servo connected to pin 1 on your pic to the center position.

    You could use a basic stamp to learn from www.parallax.com

    I use a number of compilers/interpreters but the easiest which is similar to the BS2 language is MBasic from www.basicmicro.com.

    The later option is not cheap but worth the money.

    If you want to still use the h-bridge method, a good option for an all in one chip is an L293 chip.

    Here is a link on where to buy from, how to hook it up with example code.

    http://www.me.umn.edu/courses/me2011...L293/L293.html
    Check out my hopefully useful site...

    www.hobbybotics.com

    It's still under design but it is functional

  9. #149
    Variable Bitrate brooksware2000's Avatar
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    Also, if you use a servo, you could have your code to store the current position in memory in case power is cut. Upon startup, the code pic will read current position from memory. If the current position stored = new position, the pic will do nothing. Also, the pic will command the servo to the specified position and send a refresh to the pic to hold it in position. You don't want to try and move the servo back by hand, that can damage it, but yes it will return the the commanded position. The rate/duration of the pulse does tell the servo where to go and how fast. There are premade servo controllers. One I remember off hand is from www.seetron.com.
    Check out my hopefully useful site...

    www.hobbybotics.com

    It's still under design but it is functional

  10. #150
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    Maybe the work I did a few years ago may help save you some time and effort. The controller I built used a PIC processor controlling 1 or 2 servos with all settings including end stops, time delays and speeds stored in the processors flash memory and set using 2 buttons. All the info you should need, including the code, linked below.

    http://www.atst09.dsl.pipex.com/servo.html



    Have fun

    Sproggy

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