Calculating Torque to Accelerate

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Discussion Overview

The discussion revolves around calculating the horsepower and torque required to accelerate a fixed assembly consisting of a pipe and a plate through a 180-degree rotation in 10 seconds. Participants explore the underlying physics, including moment of inertia, angular velocity, and acceleration, while seeking clarification on the calculations involved.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant presents calculations for torque and power based on moment of inertia and angular acceleration but expresses uncertainty about the results.
  • Another participant questions the interpretation of angular acceleration, suggesting that the angular speed would be zero at the end of the 10 seconds, indicating a need for constant acceleration and deceleration phases.
  • Further clarification is sought regarding whether the assembly is to be rotated continuously back and forth or just accelerated to 180 degrees and then stopped.
  • Participants discuss the need for constant acceleration from 0° to 90° and then deceleration from 90° to 180°, raising questions about the required acceleration values.
  • One participant mentions using a hydraulic motor for the rotation and seeks to determine the necessary torque for this operation.

Areas of Agreement / Disagreement

There is no consensus on the correctness of the initial calculations, and multiple interpretations of the acceleration and rotation process are present. Participants are exploring different aspects of the problem without reaching a definitive agreement.

Contextual Notes

Participants have not resolved the assumptions regarding the nature of the acceleration and deceleration phases, nor have they clarified the specific angular speeds at the start and end of the rotation.

ram18
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Hi,
I need to find out horsepower to accelerate pipe (40ft long) which is fixed with the plate (10ft x10Ft x 1inch) and whole assembly supported with bearing and shaft. I need to accelerate and decelerate this assembly 180 degree in 10 second ?

Plate weight = 4000 lb
pipe weight = 4500 lb
total weight = 8500lb.

bearing and shaft is perpendicular with respect to plate and pipe in the center

I done this calculation but its seems wrong can anybody tell me what i have to do for right solution . where i am wrong ?


Torque = moment of inertia x Angular acee

Power = Torque X angular velocity.

so i find out moment of inertia for plate and pipe .
Plate
Moment of inertia = mass X a X a / 6 = 4080 X 10x10 / 6 = 68000 lb-ft2.

Pipe ,

Moment of inertia = 647441.66 lb - ft2

Total M.O.I = 715441.66 lb - ft2.

i want to rotate this thing 180 degree in 10 second. so i consider 3 rpm .

angular velocity = 2pixn / 60 = 2x3.14 x3 / 60 = 0.314 rad/sec

angular aceen = change in velocity / time interval = 0.314 / 10 = 0.0314 rad / sec2.

avg angular velocity = 0.314 / 2 = 0.157 rad / sec

torque = total m.o.i x angular acee = 715441.66 x 0.0314 = 22464.86 lb-ft2 / sec2

power = torque x avg angular velocity = 22464.86 x avg angular velocity = 22464.86 x 0.157 = 3526.848 lb-ft2 / sec 3.

1 hp = 17696 lb- ft2 / sec3

so 0.30 hp required to rotate whole system in 10 second. it seems wrong. Can you guys give me some direction on that.

Thanks.
 
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hi ram18! :smile:
ram18 said:
I need to accelerate and decelerate this assembly 180 degree in 10 second
…
angular aceen = change in velocity / time interval = 0.314 / 10 = 0.0314 rad / sec2.

doesn't it mean that the angular speed will be zero every 10 seconds, with a constant acceleration for 5 seconds, and then a different constant acceleration for the next 5 seconds?
 
Actually i want to accelerate that assembly 180 degree in 10 second. I think all load is carrying by bearing so how can i calculate how much torque required to rotate this whole assembly. i m so confused now please give me some right direction.
 
ram18 said:
Actually i want to accelerate that assembly 180 degree in 10 second.

do you mean from 0° to 180° in 10 s, then from 180° back to 0° in the next 10 s, and so on? :confused:
 
Yes tiny tim can u help me on that .
 
ok, then that means that you need constant acceleration from 0° to 90° in 5 seconds, then an equal constant deceleration from 90° to 180° and back to 90° in 10 seconds, and so on …

how much is that acceleration? :smile:​
 
Actually i want to rotate that system 180 degree in 10 second . can u tell me my above calculation is right or wrong for that please.

Thanks,
 
ram18 said:
Actually i want to rotate that system 180 degree in 10 second . can u tell me my above calculation is right or wrong for that please.

Thanks,

I don't understand …

what angular speeds do you want it to have at the angular displacements of 0° and 180° ? :confused:
 
i am going to use hydraulics motor to rotate that system 0 to 180 degree . And i want to know how much torque required to do that?
 

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