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DC Motor control system question- random reversals

  1. Jul 15, 2009 #1
    Hello I have a project in the works that requires a DC motor to turn a somewhat heavy (but with good bearings) gear assembly. The whole thing will be running off of a common computer power supply at 12V. I haven't selected the motor just yet but am leaning toward maybe an old cordless power drill motor or something similar.
    My question is this: Is there any easy way to make the motor reverse direction at random intervals on its own from time to time? The gear assembly is a little heavy so I imagine I'd have to include some small wind-down interval between the direction changes so I don't jar the gears or cause undue stress on the system. I may need to experiment a little before I decide whether to run the motors directly from the power supply or whether I will need a PWM to dial-in the proper motor speed so maybe you could split the answers into 2 different avenues- direct vs PWM'ed. I have a pretty good working knowledge of wiring and some basic electronics but things like programming microprocessors are a little over my head. Does anyone have a K.I.S.S. solution like the inclusion of some commonly available retail device that can be repurposed or something like that? If not that, then maybe I need some relays hooked to a 555 timer?
    Thanks in advance for your help. Even if we don't come up with a working solution, I hope this is at least a fun exercise in problem-solving.

  2. jcsd
  3. Jul 15, 2009 #2
    I have the coolest idea but it is probably not what you want, anyhow, search for chaotic Lorenz waterwheel and see if you like it !

    It relies on a very simple mathematical principle and I don't know if you can build the electrical version of it.
  4. Jul 15, 2009 #3
    Wow that IS really cool! Unfortunately I don't think it would work with this project, but I've definitely earmarked it for a future contraption. Thanks!

  5. Jul 15, 2009 #4


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    Don't rule out microntrollers so quickly. They are actually very easy to learn to use and program; the BASIC Stamp series is particularly simple for novices and even the PIC series is relatively easy, once you understand the basics.
  6. Jul 15, 2009 #5


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    Yes. Microprocessors could do exactly what you want.

    For example, you could set up a Picaxe 08M chip with a programming cable connected to your computer for under $20. This depends on getting a 5 volt supply from somewhere, but the "games" port in older computers provides an easy way of getting 5 volts.

    The programming language is simple. It just tells the processor to do things in the order you want them done.

    In this case, you would also need a power transistor and a relay to reverse the motor direction.

    The chips can generate random numbers if you want random reversals. They can also do PWM in steps of 0-255 giving you excellent control.
  7. Jul 15, 2009 #6
    I actually bought a BASIC stamp a few years back but never got around to setting it up. I know some basic (and BASIC) programming so MPs/MCs always seemed like something I could probably get my head around if I needed to but again, just never had the time to sit down and learn it. So, maybe not "over my head" but just "functionally impractical". I've just learned that Arduinos have a PWM output built in so maybe that would be the wiser way to go, after all.

  8. Jul 15, 2009 #7


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    The Stamp would be fine. It probably cost you heaps, so it would be good to get it going.
    Why not drag it out and set it up? It will be time well spent.

    Picaxes use a similar language to Stamps and, like them, have a good help system and plenty of people who can help you if you need it.
    They are also a LOT cheaper so if you might be making a few projects, Picaxes are a much better way to go.
  9. Jul 15, 2009 #8
    Thanks for all your help, everyone! I cant find the BASIC stamp so I think I'll be going with either the Picaxe or the Arduino.

  10. Jul 15, 2009 #9


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    Look for PH Anderson in USA. They carry both types.

    The Picaxe is easy to use without the various development kits which add a lot to the price.

    Just get the chip and download the programming editor from Rev Ed in Britain.
    You can make up a simple cable from an old mouse cable and two resistors or buy a plug and wire it up yourself.
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