Sizing a DC motor to move a weight and counterweight

In summary, the conversation discusses sizing a DC motor for an automatic door enclosure and the suggestion of using a counterweight to ease the load on the motor. It is mentioned that power and torque are important factors to consider, as well as overcoming friction and the need for deceleration. Suggestions for finding the best motor are also recommended.
  • #1
Bobalony
3
0
This might be a silly question for some but I was wondering how do I size a DC motor to move a weight and counter weight? Suggestions for a better design are also welcome.

I want to build an enclosure with an automatic door (simple limit switches and an arduino to flip the motor on and off). But lifting the door seemed like it would take a large motor since the door is most likely going to be plywood and several feet x several feet. So I thought why not counterweight it to ease the load on the motor. But its been a long long time since I took physics so I don't really know how to find what size motor I will need. Or if there is anythign I'm forgetting to take into account here. So I thought I'd ask you guys.

I'm attaching a picture of what I had in mind in case my explanation wasn't great.

Thanks in advance.
 

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  • #2
Have a think about how quickly the door needs to move and accelerate. For example after time t it needs to be moving with some velocity v so it will need to have been given energy...

= 0.5mv2.

now

Power = energy/time

So the power will be at least

= 0.5mv2/t

To that you need to add power to overcome friction. If friction force is f then the power required to overcome friction is f * v.

There is more to it.. At some point you have to slow or even brake the motor to stop the mass of the door and counterweight crashing into the end stops. Simple limit switches and friction might not be enough to decelerate the door in the available distance.

If you are actually planning to build this perhaps look into commercial garage door openers.
 
  • #3
So I thought why not counterweight it to ease the load on the motor. But its been a long long time since I took physics so I don't really know how to find what size motor I will need.
I do not understand the picture, but counterweight is a great idea. The motor then needs to overcome only the force of friction. If the bearings and joints are well oiled so the friction is small enough, even a small torque motor should suffice. The power of the motor should not be that important, if you can wait a while for the opening. The important thing is to have enough torque (moment of force), which depends on the amount of friction and the radii of the sprocket wheels.

I think best would be to ask someone who already has such setup or find the best motor by trying the ones you can get your hands on.
 

FAQ: Sizing a DC motor to move a weight and counterweight

How do I determine the weight and counterweight needed for a DC motor to move a specific object?

The weight and counterweight needed for a DC motor can be determined by calculating the torque required to move the object. Torque is equal to the force applied multiplied by the distance from the center of rotation. By knowing the weight of the object and the distance it needs to be moved, the required torque can be calculated. The counterweight should be equal to or greater than the weight of the object to ensure proper balance and movement.

Can I use a DC motor with a higher or lower horsepower rating for my application?

It is important to carefully select a DC motor with the appropriate horsepower rating for your application. Using a motor with a higher horsepower rating can cause the motor to overheat and potentially damage it. On the other hand, using a motor with a lower horsepower rating may not provide enough power to move the weight and counterweight efficiently. It is best to consult with a professional or use a motor sizing calculator to determine the right horsepower for your specific application.

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

In a DC motor, speed and torque have an inverse relationship. This means that as torque increases, speed decreases and vice versa. It is important to consider this relationship when selecting a motor for your application. A motor with a higher torque rating will be able to move heavier weights, but at a slower speed. On the other hand, a motor with a lower torque rating will move lighter weights at a faster speed.

How do I determine the appropriate voltage and current for a DC motor?

The appropriate voltage and current for a DC motor can be determined by considering the motor's power rating, which is typically given in watts. To calculate the current, divide the power rating by the voltage. For example, if a motor has a power rating of 100 watts and is supplied with 12 volts, the current would be 100 watts / 12 volts = 8.33 amps. It is important to ensure that the power supply can provide enough voltage and current for the motor to operate properly.

Can I use a DC motor to move weights in both directions?

Yes, DC motors are designed to rotate in both directions, making them suitable for applications that require movement in both directions. This can be achieved by reversing the polarity of the power supply, which will change the direction of the motor's rotation. However, it is important to consider the motor's torque and speed ratings for both directions to ensure it can effectively move the weight and counterweight in both directions.

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