# Specification of DC motor for my project work?

• IamDev
In summary, the customer needs a DC motor for their project work involving rotation of a cylindrical disk of 1 kg, inside water (approx. 2 cm below the water level). They are not sure of the power or torque that they need, but they have done calculation. They would like to know what computer/analog electric circuit and driver (servo-amplifier) are necessary, as well as how to control the speed of the motor. If the motor is to be used for hobby, they would like to look into using a stepping-motor instead.
IamDev
Hello,
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.

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 ).

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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.

-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/encoder-dc-servo/planetary-encoder-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?https://www.physicsforums.com/attachments/83456 View attachment 83457

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## 1. What is the purpose of specifying a DC motor for my project work?

Specifying a DC motor for your project work is important because it ensures that you have the right motor for your specific application. The motor specifications will determine its performance and capabilities, which can greatly impact the success of your project.

## 2. What are the key specifications to consider when selecting a DC motor?

The key specifications to consider when selecting a DC motor include voltage, current, speed, torque, size, and efficiency. These specifications will determine the motor's power, speed, and overall performance.

## 3. How do I determine the required voltage and current for my DC motor?

The required voltage and current for your DC motor will depend on the power requirements of your project. You can calculate the necessary voltage and current by considering the power output of your motor and the voltage and current ratings of the motor's power supply.

## 4. What is the relationship between speed and torque in a DC motor?

The speed and torque of a DC motor are inversely proportional. This means that as the speed increases, the torque decreases, and vice versa. It is important to consider both speed and torque when selecting a DC motor to ensure that it can meet the requirements of your project.

## 5. Can I use a DC motor with a different voltage or current rating than what is specified for my project?

It is not recommended to use a DC motor with a significantly different voltage or current rating than what is specified for your project. Doing so can result in poor performance, damage to the motor or other components, and potential safety hazards. It is best to choose a motor with specifications that closely match your project's requirements.

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