Calculating Mass Moment of Inertia for a Roller Door

In summary, the conversation discusses the concept of mass moment of inertia and how it applies to a roller door that curls around a drum. The question is whether the mass moment of inertia of the door is the same when it is coiled around the drum as it is when it is closed, and the suspicion is that it is not. The conversation also mentions the physical attachment of the door to the drum and the need to factor in the drum inertia in the inertia equation. The suggested method for finding the correct torque needed to open and close the door involves calculating the torque exerted by the fully extended door and the torque needed to spin the drum when the door is fully opened. There is also a note about estimating the resistance of the door to being
  • #1
exidez
44
0
This is not a question from any textbook or assignment. It is a concept question in order to get a task done. I need to size a motor but just need to confirm my suspicion.

I am sizing a motor needed to open/close a roller door that curls around a drum. Not one of those modern ones. I need to have an estimate of the mass moment of inertia of the door.

My question is, if i calculate the mass moment of inertia of the door (about the axis of the roling drum) when it is coiled around the drum, is this the same as the mass moment of inertia of the door when its is closed (ie. similar to a hanging mass)?

My suspicion is that it is not and the mass moment of inertia is larger when the door is close (like a hanging mass from the drum)

The door is physically attached to the drum and the drum is not used a pulley.

//Edit
I just realized i think i am completely misunderstanding the concept. Mass moment of inertia is greatest when it is coiled up. When it is extended (like a hanging mass), there is just a load torque being applied to the drum. Only the drum inertia needs to be factored in the inertia equation.
 
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  • #2
Yes, I don't know the answer, but try calculating the torque the door will exert when its fully extended, and then calculate the torque needed to spin the drum when the door is fully opened, and see which is greater, and go by that value.

You'll need some way to estimate the resistance of the door to being rolled up though.
 

1. What is mass moment of inertia?

Mass moment of inertia is a measure of an object's resistance to rotational motion. It is also known as rotational inertia or moment of inertia.

2. How is mass moment of inertia calculated?

The formula for calculating mass moment of inertia is I = ∫r² dm, where r is the distance from the object's axis of rotation and dm is the differential mass of a small element of the object.

3. What factors affect mass moment of inertia?

The mass, shape, and distribution of mass within an object are the main factors that affect its mass moment of inertia. Objects with larger mass and mass farther from the axis of rotation will have a higher moment of inertia.

4. What are the units of mass moment of inertia?

The SI unit for mass moment of inertia is kg·m², but it can also be expressed in other units such as lb·ft² or slug·ft² in the English system.

5. Why is mass moment of inertia important in physics and engineering?

Mass moment of inertia is important because it helps determine an object's resistance to rotational motion, which is necessary for understanding and predicting how objects will behave under different forces and torques. It is also crucial in designing and optimizing mechanical systems such as engines and motors.

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