The torque required to rotate 675 lbs mass?

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Discussion Overview

The discussion focuses on calculating the torque required to rotate a 675 lbs mass for maintenance purposes. Participants explore various factors influencing torque, including the mass properties of the equipment, the center of gravity, and the method of operation. The conversation encompasses theoretical considerations and practical applications related to the design of a fixture for this task.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant inquires about the moment of inertia (MOI) of the object, suggesting it is crucial for torque calculations.
  • Another participant provides detailed mass properties of the equipment, including its center of mass and moments of inertia, which are necessary for further analysis.
  • Questions are raised regarding the mounting of the equipment to ensure the center of gravity is aligned with the axis of rotation, along with tolerances for this alignment.
  • Participants discuss the worst-case scenario for torque calculations, considering the center of gravity's displacement from the axis of rotation.
  • There is a query about the force a typical person can exert on a handwheel, leading to considerations of the minimum diameter required for effective operation.
  • One participant questions the necessity of a handwheel, asking if the operator could turn the object directly, indicating a potential alternative approach.
  • The speed at which the operator needs to turn the equipment is also discussed, with implications for whether acceleration and deceleration torques need to be factored into calculations.
  • A mathematical expression for torque is presented, emphasizing the relationship between torque, moment of inertia, and angular acceleration, while also noting the importance of the axis of rotation.

Areas of Agreement / Disagreement

Participants express various viewpoints and raise questions without reaching a consensus. Multiple competing considerations regarding the method of operation, torque calculations, and design requirements remain unresolved.

Contextual Notes

There are limitations regarding assumptions about the mounting and alignment of the center of gravity, as well as the specific conditions under which the torque calculations are to be made. The discussion does not resolve these dependencies or assumptions.

shawnycoconut
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Hello everyone,
I am trying to design a fixture that can clamp onto and turn an equipment 180 degrees for maintenance.
I am trying to figure out what torque will be required at the hand wheel to turn it.
The piece of equipment will be clamped at its center of gravity. However, its mass is not symmetrical.

Pleases guide me along this problem. Thank you
 
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Welcome to PF.

What is the MOI of the object?
 
Here are the mass properties of the equipment that needed to be turned.
source: Solidworks Mass = 673.280 pounds

Volume = 3065.995 cubic inches

Surface area = 9939.267 square inches

Center of mass: ( inches )
X = 0.012
Y = 7.023
Z = 0.002

Principal axes of inertia and principal moments of inertia: ( pounds * square inches )
Taken at the center of mass.
Ix = ( 0.000, 1.000, 0.001) Px = 23871.534
Iy = (-0.997, 0.000, 0.072) Py = 37167.538
Iz = ( 0.072, -0.001, 0.997) Pz = 37745.029

Moments of inertia: ( pounds * square inches )
Taken at the center of mass and aligned with the output coordinate system.
Lxx = 37170.503 Lxy = 1.103 Lxz = -41.273
Lyx = 1.103 Lyy = 23871.541 Lyz = 9.484
Lzx = -41.273 Lzy = 9.484 Lzz = 37742.057

Moments of inertia: ( pounds * square inches )
Taken at the output coordinate system.
Ixx = 70379.321 Ixy = 55.828 Ixz = -41.258
Iyx = 55.828 Iyy = 23871.633 Iyz = 18.187
Izx = -41.258 Izy = 18.187 Izz = 70950.963
 
shawnycoconut said:
Pleases guide me along this problem.
1) How will you get it mounted so that the CG will be on the axis of rotation? What is your location tolerance?

2) Given the worst case location tolerance (CG farthest from axis of rotation), what is the worst case torque (CG is horizontally displaced from axis of rotation)?

3) How much force can a normal person exert on a handwheel handle? From that, calculate the minimum handwheel diameter.

4) Is there a reason why the operator cannot turn it by grabbing the object directly? No handwheel.

5) How fast does the operator need to turn it 180 degrees? If more than about 10 seconds, then acceleration/deceleration torque can be ignored. I faster than 4 or 5 seconds, then you need to calculate acceleration/deceleration torque about the axis of rotation.

The above is enough for you to get started. Work through the above carefully, then we can help you with the next steps.
 
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jrmichler said:
4) Is there a reason why the operator cannot turn it by grabbing the object directly? No handwheel.
Excellent question!
 
$$ \sum T = I \frac{d^2 \theta}{dt^2}$$

What is the moment of inertia of the body about the axis you wish to rotate it about? Your coordinates of the mass center and MOI calculated by the program are RELATIVE to the CM coordinate system in your 3D model. Which axis are you rotating about. Is that axis coincident with a principal axis? I simple diagram of the part ( indicating the axis of rotation ) would greatly help.Then you are going to have some opposing torque that is a function of the bearing load ( and the quality, type of bearing), and a torque applied by the operator ( through the wheel )
 
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