How to choose geared DC ? :]

Discussion in 'The Projects Forum' started by aGpLT, Mar 3, 2010.

  1. aGpLT

    Thread Starter Member

    Jan 21, 2010
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    Hello everyone, i am doing project robot arm and i used dc geared 2.4V 1A motors and they are to weak. So i am searching for stronger motors and i dont know how to choose properly, could someone help me ? Ask something if you need more detailed information :]
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    If we do not know everything about the arm and the desired mass to be moved, all we can do is guess.
     
  3. aGpLT

    Thread Starter Member

    Jan 21, 2010
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    Ok, i will put one photo of my project it will tell you more than i can with my english :] So you see this arm is something like letter "Z" desired mass hmm its something like to be able to pick a little box. :]

    some pics:

    http://www.ipix.lt/images/11611085.jpg
    http://www.ipix.lt/images/40808497.jpg
     
    Last edited: Mar 3, 2010
  4. aGpLT

    Thread Starter Member

    Jan 21, 2010
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    So no one can can help me ? ;] sorry for impatience just i need to know in these days. Just i am quite new with motors and really don't have any idea which one to chose.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    I see the pix, but the motor has only the function of closing/opening the gripper? Do you have a figure for the torque produced by the current motor, and have an idea of what the desired torque might be?

    And do you have a source of surplus motors to be able to obtain a cheap replacement?
     
  6. aGpLT

    Thread Starter Member

    Jan 21, 2010
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    Yeah it's. Hmm about torque i don't have any idea, sorry. What you mean by last question, can't understand, are you asking, do i know where to get cheap motors ? :]
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
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    Use "surplus dc motors" as the Google search term. You may want to go up to 12 volts for the power.
     
  8. aGpLT

    Thread Starter Member

    Jan 21, 2010
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  9. BMorse

    Senior Member

    Sep 26, 2009
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    NO, you will need a motor with a gearbox on it to increase the torque output of the motor to be able to move something heavy with it....

    similar to something like this rated at 12/24 volts, 2 amps...

    [​IMG]

    B. Morse
     
  10. aGpLT

    Thread Starter Member

    Jan 21, 2010
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    Under load (4.2Ncm) speed is 715rpm, current drain is 0.75A @ 13vdc. or
    12vdc gearhead motor produces 18kg-cm torque @ 27RPM with only 330ma current drain. 2 amps i think is to much for me i mean for my controller, max current per channel is 2 amp.
     
  11. BMorse

    Senior Member

    Sep 26, 2009
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    It was just an example of what you need to look for in a DC Gear Motor.... there are plenty out there that draw less current... Just because a motor is rated at 2 amps doesn't mean it will always draw 2 amps... it all depends on the load on the motor....

    B. Morse
     
  12. aGpLT

    Thread Starter Member

    Jan 21, 2010
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  13. BMorse

    Senior Member

    Sep 26, 2009
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    that says the stall current is 2.2 amps, I thought your driver can not handle anything above 2 amps??

    And this has been altered to be used as an AC generator..... don't think that would work for your application..notice the 4 leads coming out of the motor??

     
  14. aGpLT

    Thread Starter Member

    Jan 21, 2010
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    But as you said it doesn't mean that it will use so much it depends on load. hmm, i thinked that if i only use two wires it will work fine without that generator :]
     
  15. retched

    AAC Fanatic!

    Dec 5, 2009
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    How much does the arm weigh? how much do you want it to lift?

    You should not have picked a controller until you have chosen what motor to use. And you can't choose the motor until you know how much weight you need to move.
     
    Last edited: Mar 4, 2010
  16. aGpLT

    Thread Starter Member

    Jan 21, 2010
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    am its really light because arm is made from veneer, i think it would be near 1kg without motors on it. that box weight is about 200g which i need to move. < approximately. I can't really say exactly because i can't measure it. These motors which i have now at start worked perfectly i mean without controller it could work normal without problems, but when i made controller and tryed again it couldn't lift hand, dunno why, and now without controller is the same so i think i need more power. But i can't choose correctly because i really don't know which ones are good enough.
     
  17. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Amount of power depends in part on how fast arm needs to move, what lowest angle arm makes with base, pitch of drive screw? Motor looks good to me, might add low value resistor in series with motor for current sensing to avoid stall current. Use AC later for feed back.
     
  18. retched

    AAC Fanatic!

    Dec 5, 2009
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    If the motor worked fine before the controller, You don't want that controller.

    You should use a PWM control for the motor. That will allow you to use the motor at proper "strength" by using it full voltage and current. The PWM turns the motor on and off VERY VERY fast to change the speed in which it spins. The controller you are using is most likely reducing the voltage to the motor to slow it. That, inturn, is also weakening it.

    ---- So, you are saying that without the controller, the motor is not too weak. Correct?
    --- With the controller, the motor is to weak. Am I right?

    Do you have access to a 555 timer chip? or a microcontroller?
     
  19. aGpLT

    Thread Starter Member

    Jan 21, 2010
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    For me speed is not main aspect, i need just to move it :]

    1. about this angle you are talking ? http://www.ipix.lt/images/28162567.jpg
    2. AC generator for feed back, have any link, i searched but can't find :]

    Yeah i heard about PWM but never tryed it. My controller is L298 it have voltage drop ~1.8-3.2V supply of controller is 5V my motors are 2.4V.

    1. Yeah at first without controller it worked perfectly. (used 5V for motors directly)
    2. With controller motors don't have enough power.
    3. when i tryed another time the same as 1. it didn't worked. so that's why i am searching for new motors.
    4. I have microcontroller PIC16F88 i will be using it to control arm.
     
  20. retched

    AAC Fanatic!

    Dec 5, 2009
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    The PIC16F88 has built in PWM. You can use that for the motor control.

    What you may want to consider, is stepper motors. Stepper motors can be moved one "step" at at time, giving you greater control over your movements. You can also "micro-step" the motors to get even more control over your arm.

    They are rated in holding-strength. That is how much weight they can hold still.
     
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