VERY new need help with project DC 12v

Discussion in 'General Electronics Chat' started by crowe, Oct 29, 2011.

  1. crowe

    Thread Starter New Member

    Oct 29, 2011
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    Hey everyone! First of all, I AM NEW to electronics, electric motors, etc. so, please don't hammer me immediately and please try to stay basic in your replies. I appreciate your efforts!

    I am trying to build a simple pulley system (1 drive pulley, one slave/idle pulley). the Two pulleys/poles approx 30-50 yrds apart, and use 100lb mono fishing line as the "belt". My power supply is a 12v dc car battery. I have a 12v 2.9amp motor with a pulley mounted on shaft....acting as my drive pulley. I also have a 12v 15 amp PWM to control the speed of the motor/pulley speed.

    Here is where my problem starts (well one of them).....I need to be able to set a "run time" or "cycle time" "# of revs" I really don't konw the correct terminology. The motor needs to run in one direction X feet, stop for a second, then reverse to the original position continuously repeating without me sitting there hitting a switch at the end of every run. How can I accomplish this? Is there something that is prefab I can order? If so, where? If there were a simple way to program a run-time or # of revolutions per cycle that would be great.

    thanks

    Crowe
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    Welcome to AAC! We like helping beginners here, so you have come to the right place.

    The first thing that comes to my mind is sensors. You sound like you need something to measure distance.

    The approach I would likely use is a magnet on the wheel to count rotations. The pickup could be either a reed switch or a hall effect switch (does the same job as a reed switch, but is purely electronic).

    How do you decide how many feet you need to go?
     
  3. crowe

    Thread Starter New Member

    Oct 29, 2011
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    the distance really depends on the set-up....I would be happy even if I could have system that remained fixed....ie 30yds or so. I'm not sure about using a magnet to measure....I was simply going to measure the circum of my pulley and then count/program # of revs. so if it is 1ft in circum then 90 revs would be 30yds...etc.
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    There are several ways of doing this, I didn't think of it at the time, but there is also stepping motors, where they rotate a fixed number of degrees when sent a pulse, no sensors needed. However, they tend to be weak, and the interfacing circuitry can be a bit overwhelming.

    One of the problems you are going to face is you have jumped immediately into intermediate electronics as opposed to basic stuff. This means you will likely have a major learning curve. There will be other people who will step in and help, my personal time is spread thin at the moment, but I can prep the way with questions.

    The first thing I thought of when reading your post was counters. This is a type of circuit that, as the name suggests, counts. There are many, many IC chips that are counters.

    Is this going to have to be a strong motor, or is it driving a light load? How big is the circumference of the wheel? This will dictate the approximate number of turns you have to track.

    There is also a kind of circuit out there called a microcontroller. Several manufacturers make them, basically it is a small computer on a chip with pins left open for inputs and outputs. The ability to program them with software saves oddles of hardware. I have seen people with absolutely no electronics experience use them, but this is people who like to write software. Again, steep learning curve of a different sort, but very useful to know.

    BTW, the magnet was to count the number of turns of the drive pulley. Did you have an alternate way in mind to count revolutions of the wheel? This is a primitive form of robotics, some sensors required.

    You could use a timer, but this is extremely crude and will drift badly over time.
     
  5. Maketronic

    Active Member

    Mar 21, 2009
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    Hi. If you already have alot of the gear described in your original post one option would be to use a timer and a h bridge connected to the output. For a beginner I would suggest the use of a picaxe or an arduino to run the h bridge electronics. I Suggest have H bridge run one way, pause a moment to alow motor to stop then have H bridge run the other way. Have a look on the internet there is alot of of example h bridge circuits available. This is quite a simple method but keep in mind that without feedback you might be dissapointed by the results. There are better ways to do this though.
     
  6. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Ok, most people would do this like Bill said; mount something on your motor shaft (like a magnet) that will rotate past a sensor and you can set X # of revolutions is equal to X # of feet, and set a limit to stop or reverse direction after X # of pulses/feet. This requires electronic counting of something which isn't the simplest method to accomplish the result you are after IMO. If you were able to attach a magnet (actually probably 2 magnets) to your belt, you could get this done with a couple of reed switches and a couple of relays, and might take you an hour to set up. And, if you ever wanted to change the length of run, all you would have to do is move the magnets. You would however be limited to less than one complete revolution of the belt (I hope that's not a big deal; sounds to me like you already intend to stay < 1 complete revolution). is this possible? Can you attach magnets to your belt? can you stay < 1 complete revolution? is your belt tight enough so the magnets would not be flailing around in the air like windsocks?
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    It would be helpful if you told us what the purpose of this is. Right now, we don't have any way to tell if some degree of precision is required; and if so, if the movement of the "belt" or the rotation of the idler is the important item.
     
  8. strantor

    AAC Fanatic!

    Oct 3, 2010
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    it sounds to me like a DIY gun range target placer/retreiver.
    If that's what it is, don't confirm.
     
  9. crowe

    Thread Starter New Member

    Oct 29, 2011
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    You could think of it as a target/retriever but not exactly.

    My purpose is to indeed use less than 1 rev of the belt. The belt will be 100lb mono fishing line. There isn't much resistance on the line. This will remain in the weather elements....so Im not sure how it would work in those conditions. I do like the idea of the magnets, being able to adjust them, etc. Plus in the event that the line slips on the pulley, it would simply keep turning until it triggers the switch.

    I would need to rethink the distance between the motor and the sensor. I extended the shaft of the motor to about 1ft.....so, there is 1ft between the motor and the pulley.....I dont think the magnets/sensor will pick up that far but ???? I've never done this before.. Also, How would this work on the slave end of the unit? I need to run everything from the drive side of the unit.

    I assume these magnets are small as to not put too much weight on the line.
     
  10. strantor

    AAC Fanatic!

    Oct 3, 2010
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    the simplest solution I can think of; no magets, no reed switches, no relays, no counters, no microcontrollers. Just a toggle switch and some craftiness with coat hangers.
    [​IMG]
    EDIT: if you're going to have something hanging from the bottom, just flip the picture over and do it that way
     
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