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how to compatable pick bi polar stepper motors and Transistor for the porpeller chip — Parallax Forums

how to compatable pick bi polar stepper motors and Transistor for the porpeller chip

badwawulfsbadwawulfs Posts: 4
edited 2011-09-25 15:59 in Robotics
ok im thinking to buy a High-Voltage, High-Current Darlington Transistor Array the ULN2803 DIP or ULN2003 DIP also im looking at bi polar steppers.... http://www.google.com/#q=bipolar+stepper+motor&hl=en&prmd=imvns&source=univ&tbm=shop&tbo=u&sa=X&ei=weh4TtaQKsrKsQKwhPC5DQ&ved=0CIsBEK0E&fp=1&biw=1280&bih=867&bav=on.2,or.r_gc.r_pw.&cad=b

im kinda stuck i dont know what specs i need to compare to understand if any of the parts are compatable... i have some idea.. i think the propeller has 3 volt out and i know ill need a power supply im thinking to try and use an ATX power supply and just plug it into an old motherboard to get the load on the wires. i know that if you cross the green with a ground it starts up but i head you need a load on sme of the other wires as well and for a test unit i think i can just plug in an old board for that load.

can any one requmend a good to great stepper that for a 5 axis arm tha can lift 1 or more lbs
also a chip like the Darlington Transistor Arraythat works well with the propeller chip?

and mybe a power supply.. IM really new to electronics and im finding them confusing when it comes to understanding what parts work with others and such.

thanks! awsome forums!! i read the colum #6 in the nuts and volts thats where i got the ideas about the High-Current Darlington Transistor Array's and they look apealing.

regards,
sam

Comments

  • kwinnkwinn Posts: 8,697
    edited 2011-09-20 20:32
    The ULN2803 can be used with the propeller, and can drive a small stepper motor. The absolute maximum voltage it can handle is 50V, although I would not use it for more than 40V in my designs. The maximum collector current a single output can handle is 500mA, but you can not have all outputs at 500mA simultaneously. The maximum current per output with all 8 outputs conducting is ~ 160mA IIRC.
  • alex123alex123 Posts: 102
    edited 2011-09-21 07:40
    You won't be able to use the ULN2803 for a bipolar (4 wire) stepper motor because each driver there is an open collector type. For a bipolar stepper you'd need a push-pull driver like this one:
    http://www.parallax.com/Store/Components/AllIntegratedCircuits/tabid/154/CategoryID/31/List/0/SortField/0/catpageindex/3/Level/a/ProductID/608/Default.aspx

    Then again, stepper motors are usually not very high torque unless they are big and draw a lot of current. You may get 20-40 oz-in of holding torque per amp. Also the faster the stepper motors rotates the less torque you'll get.

    Your best would be to use a brushed motor with gears. If you need a precise position control use an encoder. Or just use a high torque servo if you're ok with less than 180 deg of motion.
  • Spiral_72Spiral_72 Posts: 791
    edited 2011-09-21 20:45
    Steppers are great, but in my opinion you'd be wasting your time and money using a stepper for a robot arm. A better fit would be a 1/4 scale R/C servo for an all in one package, or a DC gearmotor if you want to roll-yer-own.

    With the R/C servo, you can focus on the mechanical and programming, it's a LOT more efficient and will work better all around than a stepper.

    As a note, every high end arm (Fanuc, Staubli etc, etc) will use a servo with a gearhead.... You can't beat DC for this application :)


    Edit: That's not to say it CAN'T be done! If you wanna continue with the stepper, by all means and we'll do the best we can to point you in the right direction.

    It sounds like a nice project by the way!
  • badwawulfsbadwawulfs Posts: 4
    edited 2011-09-25 15:20
    ok cool, maybe stepper is not the way to go.

    i have been able to hook up and run a DC motor but it seems weird i have it hooked throught a transister and for some reason im thinking its feeding voltage back into the propeller chip. when i hook a diode up to prevent back feed the dc motor wont run.. is this a normal problem an inexperanced person might get with electronics? I should probly post my a picture of the wiring or a diagram.

    but i eather way i was able to get the motor to run in pulses so that was cool!

    one more question. is i have notested that the transister will only stop some electricy from flowing... so if i have 3 volts being blocked the motor will have a little resistence but not turn and i see about millivolts of voltage.. but if i drop it into a higher voltage like 9 volts the transister cant stip it and the motor spins... what can i do about that?

    thanks every one, i really feel like im making progress here with your help!

    -sam
  • kwinnkwinn Posts: 8,697
    edited 2011-09-25 15:59
    Can you post a schematic of the circuit you are using?
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