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Specification of DC motor for my project work?

  1. May 12, 2015 #1
    I need to buy a DC motor for my project work. My project involves rotation of a cylindrical disk of 1 kg, inside water (approx. 2 cm below the water level) at different speed ranging between 100 rpm -200 rpm. For this purpose I need to buy a DC motor but I am not sure of what specification I really need. I have done calculation but I am little confused as I have no idea about these things. So please someone tell me what power and what torque I need for this purpose and exact specification of DC motor to buy.
    I also need to know how can I control DC motor to run at desired constant rpm.

    I need urgent help.
  2. jcsd
  3. May 12, 2015 #2


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    Rotating a disk below water, some friction will arise. I don't know the diameter of your disk, but maybe only a rated power = 5W will be needed to overcome this friction. Anyway regarding the robustness of the motor, I would buy a motor with a rated power about 50W, and a rated speed ≈ 500 rpm ( or as low as possible, then the torque will be sufficient ) with some rigid shaft, and maybe with shafts at both ends of the motor, so that an encoder/tacho-generator can be easy mounted. I think maybe the motor must be splash-proof ?

    The control of the motor speed can be done digital ( very exact and rigid: mount an encoder ) or analog ( mount a tacho ).

    Then you need a computer/analog electric circuit as for digital/analog control, and a driver (servo-amplifier). Some programming-knowledge/screw-driver is needed to adjust the digital/analog controller.

    Have you considered using a stepping-motor instead? I think some stepping-motors will be able to run 200 - 300 rpm, and they are much easier to control. Also you can buy dc-motors with built-in encoder, controller and servo-amplifier. ( I know where to buy them, I've made them myself at an earlier job. No advertising here, but you may google: integrated+servomotors ).
    Last edited: May 12, 2015
  4. May 13, 2015 #3
    Spinning a disk in water does not describe much - size / shape of the disk, as well as the container. As the clearance between the disk and the container goes down the required torque will increase.

    Is this a work project or for home/hobby? , do you want to spend time doing it? Is this a product development (multiple unit build) ? or a one off design. In a basic design (smooth disc, large container, etc) Since most of the power will be needed accelerating (and potentially decelerating) the disk the Spec for acceleration should be defined. Also -- how and how well does the speed need to be regulated?.

    Off the bat I'll assume for hobby I would look at something like an arduino and a stepper motor ( all of the parts maybe $100 )

    If you need a ready to run solution (buy, plug in - set speed) you will probably double to triple that cost at the least.

    Lastly - an most importantly - you are mixing power and water, I know it will add cost but please consult a professional if it is for work. The hobby projects should all be using a double insulated wall transformer (wall wart) ( for example prototype with a battery initially to minimize risk) . Not to mention that electrical components do not typically last long in very high moisture environments - so finding a way to keep the motor and electronics separate from the water would also be advised. The reason for the Work / hobby distinction is that the hobby grade components are probably not rugged enough for a work environment.
  5. May 14, 2015 #4
    -Dimension of the water tank is 800x500x350mm.
    -The level of water is about 100 mm below from the upper edge of the water tank & and rotating disk is approx 1-2 cm below the water level.
    -Diameter of the disk is 150 mm and thickness is 5 mm and made of mild steel (density 7850 kg/mm3)
    -Rotational speed which I require is ranging from 100 rpm to 200 rpm.
    -I have attached the image of my setup which I need to fabricate.

    I really need the list of all things which I need to buy (with the exact specification) and somebody check this link ( http://robokits.co.in/motors/encode...coder-geared-motor-24v-175rpm-100w?cPath=2_3& ) and tell me will this motor work or not?
    What are the other things which I need to buy along with this for speed control? (try to give me some image and links)
    Can I use DC motor inside water and if not then how can I make DC Motor waterproof? View attachment 83456 View attachment 83457 Capture (2).JPG

    Attached Files:

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