micro reversing 7.2 Volt Circuit Needed

Discussion in 'The Projects Forum' started by torpedochief, Dec 8, 2009.

  1. torpedochief

    Thread Starter Senior Member

    Mar 30, 2008
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    Hello Firends,

    I am in need of a circuit that will drive a very tiny cell phone vibrator motor very slowly to the left stop then reverse and stop where it started. It all had to be automatic. I am working with 7.2 volts. Any help would sure be appreciated.

    Don

    Author of Of Ice and Steel
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    What components are you allowed to use?

    Are you familiar with PLCs or microcontrollers?

    How does the position of the motor shaft is sensed?
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    Hi Don,

    Gee, that's going to be pretty tough to do. Those little vibrator motors were designed for rather low torque and fairly high speed operation, and don't have a built-in means of reporting the position/angle of the rotor.

    You would need to add on some kind of rotational encoder, or perhaps an opto-interrupter and disk with slots in it to keep track of it's movements.

    But getting it to turn slowly would be the real challenge.

    It would be a lot easier if you could use a bipolar or unipolar stepper motor. There were a bunch of very small stepper motors made for use in 3-1/2" floppy drives and CD-ROM drives that are on the surplus market. The advantage of stepper motors is that they have a relatively high torque at low speeds, and you can step them as slowly as you like. You can also get them to return to their original position by reversing the steps.
     
  4. torpedochief

    Thread Starter Senior Member

    Mar 30, 2008
    124
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    Thanks Guys,

    I knew you could help me out. Kinda silly but this is all I am doing.

    http://www.youtube.com/watch?v=9freyDTI_IQ

    This little guy just needs to turn then come back ad the mechanism has to fit inside the Tiger Tanks Hatch.

    The tank operates on 7.2 volts. I am designingthisto be used in one of three ways. One is with just a servo (that is the easy one) This one isfor use by those who are using the Heng Long Rx-13-14 or 18 control module. It has a spare plug that can send power when activated to start the little guy moving. Thanks again and any help wouldbe very much appreciated.

    Don
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    He's pretty cool. ;)

    You really do need some kind of stepper motor driver arrangement though.

    What kind of space is available below where the tank commander goes?
     
  6. torpedochief

    Thread Starter Senior Member

    Mar 30, 2008
    124
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    Hey Sarge,

    It is a very small area. This has never been done in this scale (1/16) There is maybe and inch and a half in depth and and inch on each side. I'm fighting for space that is occupied by a main gun recoil, coax machine gun, turret rotation.

    Here is the type of tank we are dealing with. Thisis TIGER 304 I built not long ago.

    http://www.youtube.com/watch?v=4fi4I2cHy4s
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    OK.

    Ran across an Electronics Goldmine flyer the other day. They have these on sale:
    http://www.goldmine-elec-products.com/prodinfo.asp?number=G14197
    It's a miniature bipolar stepper motor, but it only has 20 steps per revolution.
    It could be stepped much more finely if you made a microstepping driver for it. A link from that page: http://www.picaxe.orconhosting.net.nz/stepdemo.jpg
    provides useful information about driving the stepper using a simple PICAXE uC.
    Oddly enough, they report it as having 24 steps per revolution, or 15° per step. However, as I suggested before, using microstepping techniques the steps can actually be much more fine.

    Here is a tiny gear reduction drive DC motor: http://www.goldmine-elec-products.com/prodinfo.asp?number=G16300
    This might be more of what you're looking for, as it has a speed of 58 RPM @ 12v. A wild guess tells me that might translate to about 34 RPM at 7.2v. That would roughly translate to about 1/2 second to turn and raise the binocs, and another 1/2 sec to return.

    You would need some method for the circuit to determine when the tank commander had return to front and center. That might involve a cam and a microswitch.
     
  8. torpedochief

    Thread Starter Senior Member

    Mar 30, 2008
    124
    6
    I think youfound just the item I need. That little Dc gear head motor seems what the doctor ordered! Now how would I make the circuit with the micro-switch?

    I sure appreciate the help. Sgt you should get you one of these tanks. Believe it or not they are really toys that we modify into veery realistic operating tanks. Ther are Shermans, Panthers, Tigers, STUGs, BullDogs, Pershings, T-34, KV-1, King Tigers, just about everything. And the circuites you could build for them! IR battle, sound module, inertia simulator. smoke generator. recoil system, just to name a few.

    Thanks again!

    Don

    Author of OF ICE AND STEEL, EPITAPH and coming soon TIGER!
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    But... we have a real M113 APC.
    And a real HMMVEE with an Avenger missile system on it.

    You should get some of these; they are a lot of fun. :)

    The .50 cal M2 Browning in the Avenger unit works really well for deterring tailgaters. :D

    A pic of the Avenger is attached; the turret is rotated to the passenger side. It's a Desert Storm veteran. You can see part of our Huey on the far left. Our A-4 Skyhawk is behind the Avenger; you can only partly make out the canopy and the nose.
     
    Last edited: Dec 10, 2009
  10. torpedochief

    Thread Starter Senior Member

    Mar 30, 2008
    124
    6
    Well here is what I had until I retired.

    [​IMG]

    That is me second from the left.
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    If you're ever in the Orlando area, you ought to stop in to the Museum.
    http://www.nwmvocf.org/
    We have all kinds of fun stuff. A couple Deuce & 1/2's, a 5-ton, a half-dozen Jeeps or so (just a few of them are operable at the moment) - plenty of toys to keep us busy.

    We briefly considered requesting a tank, but the ground iis really too soft around here; wouldn't be long before a tank would become a subterranean exhibit. :eek:

    I spent my time in Aviation. Something about airplanes that can fire missiles while doing Mach 2 just really appealed to me. :D
     
  12. torpedochief

    Thread Starter Senior Member

    Mar 30, 2008
    124
    6
    I'll be there in March. My now novel will be out and I'll be that way doing book signings. I will indeed stop by. Looks great! I'll bring the TIGEr with the operating Commander!

    Don
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    OK, back to your situation with the motor.

    Finding switches that are really small might be a problem. You might have to use PCB-type pushbutton switches to change direction/stop the motor.

    I was thinking about just using a timer to control the forward direction, but that might be cataclysmic for the T.C. if it went just a wee bit too far; it would be a shame if the binoculars exited the rear of his skull. :eek:

    So, you would need a pair of switches, and something to activate them. You might find a miniature brass collet at a store that sells model airplane parts that could fit on the motor shaft - or just make something; some kind of lever that protrudes about 90° from the motor shaft. Then line up the switches so that they either make or break contact at the limits of travel you want.

    It could even be a magnet and a couple of reed-type switches.

    Just some means of detecting that the limits of travel have been reached. Of course, it needs to be really compact.
     
  14. SgtWookie

    Expert

    Jul 17, 2007
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  15. SgtWookie

    Expert

    Jul 17, 2007
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    Last edited: Dec 10, 2009
  16. torpedochief

    Thread Starter Senior Member

    Mar 30, 2008
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    Looks Good Sarge,

    I think the relay would be best. Now how in the devil do I wire it all up? I was just about understanding the switches....LOL If I used the step motor and relay, what would that look like? Would I still need the switches? Iguess I would to let it know how far it has gone and when to reverse. What I dont understand is I apply power ad the shaft turns till it hits the switch. Onceit hits the switch the relay tells it to reverse. Then it rotates till it hits the second switch that tells it to stop. What lets power back into the circuit to start it up again? Also, could I use a resistor to slow the motor down even more if needed?

    Don
     
  17. SgtWookie

    Expert

    Jul 17, 2007
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    OK, if you used a stepper motor, you would need a microcontroller with a driver circuit to operate it. The microcontroller would also need to know where the initial start point was, so a switch or optointerrupter of some sort would be needed.

    I don't know if you have any experience with microcontrollers - but if you got to experimenting, you would be amazed at how much you can do with them.

    But right now, it would be very helpful to know if any of that stuff will fit in your tank model.

    The micro gear reduction motor would use an H-bridge relay (like I linked to) in order to reverse the direction. That will likely eliminate a lot of circuit-building.

    Now the question is - are those reed switches something that will fit, and if so, are they going to be normally open or normally closed.
     
  18. torpedochief

    Thread Starter Senior Member

    Mar 30, 2008
    124
    6
    Yes sir they will fit. So far the motor, relay and switches are fitting nicely. I forgot that the cuppola is on the tank so that gives more room. In addition I thought about the fact thatin the hull there is plenty of room for just about anything I want to put in. I just have to have the TC and the motor in the turret. I can run wires into the hull, and have the circuit mounted there.

    This is getting fun!

    Thanks

    Don
     
  19. SgtWookie

    Expert

    Jul 17, 2007
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    Oh, I happened to stumble on another circuit I drew for another tank modeler awhile back for controlling the AZ/EL of their turret, and a firing button - if you're interested. ;)
     
  20. SgtWookie

    Expert

    Jul 17, 2007
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    But before we get too distracted with that, how did you plan on activating the TC so he begins to make his move?

    Would you supply a momentary voltage or a momentary ground?

    I kinda need to know that before I start drawing something up. I'd really just like to do it once.
     
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