DC Motor SeeSaw Action

Discussion in 'The Projects Forum' started by luvv, Jun 26, 2011.

  1. luvv

    Thread Starter Member

    May 26, 2011
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    Hello,
    Before i get started,want to thank everyone involved in this site,it has been very informative/useful for me.
    That said, my goal is to get a small 9v.DC brushless motor to oscillate?..alternate?..err.forward,reverse,forward,reverse..seesaw movement.
    Now the catch,unless it is 100% necessary,i don't want to use PIC's, mechanical changeover relays,or stepper motors.
    Looking around the net, it appears the best method for controlling movement is a the "H-Bridge" and while that would work for one aspect of the problem,it doesn't solve it.
    What i need is a self oscillating action where one only need power on the circuit. Perhaps a way to integrate a timing circuit w/ the H-Bridge?..idk.

    All that is important, i must be able to vary the timing to limit travel, and vary the power to the motor, to limit it's speed.
    If i have left out some critical info. needed for a solution,just let me know.

    Thanks,
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,770
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    oscillating is not a natural motion motors are capable of doing easily.(Like making a kangaroo walk one foot at a time)

    Think about your 'needs' and re-examine how to achieve them. If you need any useable torque from the motor(plan on driving something with it) you could be forced to use a HUGE motor and correspondingly huge amounts of power to reach the point where your contraption can move an object.

    oscillating is very possible for solenoids that have a linear plunger.
    Could you drive a round gear, with a toothed plunger in a solenoid and achieve the rotary oscillations you want?

    Using a motor you might be able to force it to operate as you desire, but trying to get any useable power out of the resulting oscillations may be impossible.

    Using a stepper motor and driving it forwards and backwards rapidly is a possibility you might also consider.
     
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  3. beenthere

    Retired Moderator

    Apr 20, 2004
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    Last edited: Jun 26, 2011
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  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Piston action... yes. Good idea.

    :)
     
  5. luvv

    Thread Starter Member

    May 26, 2011
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    Thanks for the reply Kermit2
    The load on the motor is next to nill,tho i see your point.
    Stepper motor is a possibility as i have one of the correct size for the project..but that would involve further complexity in building a automatic driver to suit it.
    Again w/o the use of a PIC could be more involved than i want it to be.
    My hope was to use a 555s ability to source and sink to build some sort of push pull circuit. Don't really need much torque just a smooth controllable motion.
    I also considered a mechanical solution a reed commutator, where separate motor spins magnets that trigger 4 reed switches to alternate polarity to the "seesaw".
    Guess is this case, i want the roo to walk on different feet, ill heat the floor ;.)
     
  6. luvv

    Thread Starter Member

    May 26, 2011
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    All good suggestions, and i have considered them both.
    so to better explain my needs i'll describe the purpose of the "seesaw"

    I'm building a toy rocking horse that will sit on box,and rock a doll, the catch is the rocking horse and doll is detachable.
    So i will use magnets in the base of the horse and magnets attached to a "see saw" in side the box to rock the horse.
    Considered E-magnets in the box but the risk of fire turned me away from that idea quickly lol
    This will be a gift for my new lil niece, so no creepy noises from inside the box would be good.
     
  7. luvv

    Thread Starter Member

    May 26, 2011
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    After looking at it from the different perspective you guys offered...
    A crank assembly would do the same task, and with perfect timing..
    You guys are genius..keep it up =)
     
  8. KJ6EAD

    Senior Member

    Apr 30, 2011
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    Last edited: Jun 26, 2011
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  9. jerseyguy1996

    Active Member

    Feb 2, 2008
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    Sounds like you may have already made your choice but I will throw this out. What about a servo? It can be controlled relatively easily with a 555 timer. I made a contraption using two servos (but only because they were somewhat loaded up due to sloshing liquid):

    http://www.youtube.com/watch?v=6IWTGl0DV9o

    Also check out this video which was the 555 contest winner this year.

    http://www.youtube.com/watch?v=uXeSsevsNNE
     
  10. luvv

    Thread Starter Member

    May 26, 2011
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    I know this is a long dead thread...
    But while i was digging around for parts for my current project, i came across the finished prototype for this one.

    Maybe all the people that gave suggestions would like to see what i finally settled on.

    I used a 555 astable tied to the gates of pnp/npn mosfets, two relay coils pulled on neodymium magnets embedded in the base of the rocker.


    This is the prototype made from foamboard, the finished product was a maple horse sitting on a decorated hat box.

    So far as i know it's still rocking :p

    http://www.youtube.com/watch?v=YH-mQ89gkUQ&feature=youtu.be
     
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  11. KJ6EAD

    Senior Member

    Apr 30, 2011
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    I like the fact that it has fewer mechanical parts than the original proposal. How's the battery life?
     
  12. luvv

    Thread Starter Member

    May 26, 2011
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    Honestly i have no real idea, the board pictured is just a prototype, the final board i used i "burn tested" for 3 days running on a wall wart psu.

    I did however test the finished board on my bench top psu.
    It would operate all the way down to 5v. the finished model was far more efficient then the proto because there was no irregularity in the base of the rocker.

    Rockers want to rock by nature so it takes a very small field to to effect the balance.

    Ended up going back to e-magnets after i discovered i couldn't make a balanced crank shaft for the life of me.

    When i would get something close to workable i couldn't get motor speed just right or they make the annoying "growl".

    I doubt my sister runs it that often more likely sits on a shelf, the work my old lady did to outside made it more of a display piece them my intended toy

    -luvv-
     
  13. Kn0x_14

    New Member

    Mar 2, 2012
    6
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    could you please post your circuit diagram for this e magnet rocking horse..i think we can use it for our shaker...tnx...
     
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