Motor driven liquids stirrer

Discussion in 'The Projects Forum' started by unomi, Jan 13, 2009.

  1. unomi

    Thread Starter New Member

    Jan 13, 2009
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    Hi Guys,
    I fell over this forum yesterday and it seemed like a pleasant place to be :)

    I have been toying with some ideas for awhile and figured I'd ask you for some help.

    I live in rural Thailand so parts are not the easiest to get ahold of.

    Basically I buy fresh milk quite often, and it needs to be pasteurized(heated), milk is pretty sensitive and needs to be stirred often if not constantly to avoid undesirable changes to the milk solids.

    I would like to get into cheese production so obviously I need quite a bit of milk :)

    Anyway the basic idea is obvious and I am sure that there are commercial products out there, but this seems like a nice 'starter' project anyway.

    The first project is a stirrer embedded in the lid of a pot.
    Ideally it would be battery powered as I don't really like the idea of toying around with mains power just yet.

    It is not envisioned as a whisker so the rotational speed does not need to be high, merely enough to keep the milk in motion and have the temperature be consistent throughout.

    I have both 'standard' 'toy' dc motors and stepper motors from harddisks around, I figure stepper motors would offer the best control and also allow for best control of rotational speed and intermittent changes in directions without stressing the motor.

    However I would rather not toy around with pics or other forms of embedded programming at the moment. So I am wondering if it is possible get to a circuit that would control a stepper motor with 'conventional' electronic parts exclusively.

    Ideally id like something like clockwise and counter clockwise, speed control from 0 to 20 rpm either in steps or linearly.

    Many thanks in Advance and Happy New Year :)

    unomi
     
  2. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Stepper motor is for precise positioning control and does not normally used for applications like stirrer or blender. You are much better off using a normal motor which is far more easier to control than a stepper.

    However, normal motor runs at high rpms (few thousands ~ 50000). In order to be efficient one would need a gear box to reduce the final output speed to 0~20 rpm and get more mechanical power.
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    I used to repair chemical stirrers, very small versions of what you're talking about. They used a magnet wrapped in plastic, and the base has a couple of magnets on a shaft that was direct driven by a toy motor. Think a simple DC motor with PWM, you can even measure the speed by the magnets and a sensor (they used an optical interupt).

    The stirrer was coupled to the shaft magnetically.

    What size containers are we talking here, in meters at the base?
     
    Last edited: Jan 13, 2009
  4. unomi

    Thread Starter New Member

    Jan 13, 2009
    6
    0
    Hi.
    Thanks for the replies,
    Basically in the first instance just household pots ie roughly 15cm deep.

    I figured I would build a proof of concept first :)

    While I am not against DC motors per say, I imagined that steppers would offer better control and less in the way of points of mechanical failure.

    The chemical stirrer method I would think would probably not translate well here, as the pots are metal and HOT :)

    Thanks Again,
    unomi
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    You'd be wrong, as some of the stirrers were also hotplates. The key is the magnetic coupling, which allows the rotery motion to translate through an inch or so of material (several cm). On of the issues for the proof of concept is a lot of metals used for magnets are toxic, you have to find something that won't poisen the food (milk).
     
  6. unomi

    Thread Starter New Member

    Jan 13, 2009
    6
    0
    Right, No I don't think it would be an appropriate solution.
    Pots are abrasive and you would inevitably end up with particulates.
    I found this : http://forum.allaboutcircuits.com/showthread.php?t=15089
    Project: Torque converter for slow speed motor

    Which seems interesting, although perhaps a bit 'overengineered' for my needs, what do you think?
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    Don't know. For me it isn't the electronics, it is the mechanics. I'm getting the feeling you're coming from the other end.
     
  8. unomi

    Thread Starter New Member

    Jan 13, 2009
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    0
    Hmm, for me its both.
    I want the electronics as simple as possible as I have to build the thing :p
    I also want the mechanics as simple as possible as I have to maintain the thing :p

    I like the idea of basing it around something that can be used for other applications.
    Magnet based stirring is, I think, well suited for low viscosity liquids in containers that are 'designed' for them.

    If i can end up with a setup that can support high torque operation as well, then I can also use it for mixing in ingredients for cream cheeses for example.
    I don't like the idea of magnet mixing because it does not appear to me to scale well.

    While I would love to get you input on other applications of magnets (notably in driving 'embedded' electricity producing coils in pipes and hoses) that is something for later :)

    Ideally I would like to know if it is possible to drive a stepper motor with something like a 555 timer :)

    Regards,
    unomi
     
  9. Wendy

    Moderator

    Mar 24, 2008
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    I think you're going to have to look for scaled up mechanical versions, basically a motor, belt, and stirrer. Once you have those the rest is easy. I really liked the magnetic stirrer idea, mechanically it is much simplier, no drive shaft going into the can, for example.
     
  10. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    You can hunt around sites like American Science & Surplus for gearmotors - some take 12 volts DC in but run the output shaft at a low RPM. That could be suitable for stirring and you get much better torque thanks to the reduction graring.
     
  11. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,671
    899
    I would not recommend a magnetic stirrer for large batch production, particularly if you cannot see the material being stirred at all times. They can be somewhat tricky to keep consistent and at slow speed. In the northern hemisphere, I prefer ones that turn CCW. (No experience in the southern hemisphere.)

    Overhead stirrers (whether mounted to the vessel top or through a bushing in the top) are quite reliable and easy for large batches. Most of the ones I have seen use a gear motor. A variable speed electric drill works well. The chuck helps in assembly and disassembly. Rotation direction is not an issue with overhead stirrers. Battery power does not sound too practical as typical pasteurization time is about 30 minutes or more.

    John

    Edit: Commerical pasteurization processes are done with relatively short times. The period of 30 minutes applies to "classical" low-temperature batch processes, not continuous flow, high-temperature processes.
     
    Last edited: Jan 13, 2009
  12. Wendy

    Moderator

    Mar 24, 2008
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    I like that thought, an eletric drill, with a long shaft/stirrer in the chuck. Mechanically simple, easy to maintain, and cheap.
     
  13. unomi

    Thread Starter New Member

    Jan 13, 2009
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    0
    Yeah I like it also,
    I could retain the 'drill bit holder' mechanism for attaching the stirrer,
    The torque converter from the projects collection would get me started.
     
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