Finding Torque Without An Angular Acceleration (stepper motor)

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Discussion Overview

The discussion revolves around determining the torque required for an electric stepper motor to rotate a large thin disk. Participants explore the challenges of calculating torque without direct knowledge of angular acceleration, particularly when the motor operates between near constant velocities and instantaneous stops.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant notes the difficulty in finding torque without knowing angular acceleration and suggests that the moment of inertia is straightforward to calculate given the disk's dimensions.
  • Another participant asks about the stepper motor's datasheet, specifically the available torque per step and the degree of rotation per step, indicating that the steps are not instantaneous.
  • A later reply emphasizes the importance of knowing the torque needed to select an appropriate motor, suggesting that the datasheet could provide insights into the motor's capabilities.
  • Additional details are provided about the disk's material (6061 aluminum), dimensions (1/4" thick, 15" radius), and the desired rotation (40 degrees over 3.5 seconds).

Areas of Agreement / Disagreement

Participants do not reach a consensus on how to determine the torque without angular acceleration, and multiple viewpoints regarding the use of datasheets and motor specifications remain present.

Contextual Notes

The discussion highlights the dependence on the motor's specifications and the assumptions regarding the operational characteristics of the stepper motor, which may not be fully resolved.

Tyler
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A friend of mine posed a question to me the other day and I can't seem to wrap my head around it.

He's working with an electric stepper motor to turn a large thin disk, but he can't be sure of the torque required because to find the torque he needs the moment of inertia and the angular acceleration. The moment of inertia is easy to find since he has all of the disk's dimensions, but the electric stepper motor is taking the thin disk from 0 to a near constant velocity and back down to zero almost instantaneously.

Is there some other way to find the torque/angular acceleration that I'm just not thinking of?
 
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Tyler said:
A friend of mine posed a question to me the other day and I can't seem to wrap my head around it.

He's working with an electric stepper motor to turn a large thin disk, but he can't be sure of the torque required because to find the torque he needs the moment of inertia and the angular acceleration. The moment of inertia is easy to find since he has all of the disk's dimensions, but the electric stepper motor is taking the thin disk from 0 to a near constant velocity and back down to zero almost instantaneously.

Is there some other way to find the torque/angular acceleration that I'm just not thinking of?
What does the datasheet for the stepper motor say for the available torque per step? How many degrees is each step? The steps are not "instantaneous" -- the datasheet should give some idea of the time per step that is advised (depends on drive voltage and current)...
 
berkeman said:
What does the datasheet for the stepper motor say for the available torque per step? How many degrees is each step? The steps are not "instantaneous" -- the datasheet should give some idea of the time per step that is advised (depends on drive voltage and current)...
Well, therein lies the catch. He's trying to pick a motor based on the amount of torque he needs, or at the very least trying to verify that the motor he is looking at is more than enough for the task.
 
Tyler said:
Well, therein lies the catch. He's trying to pick a motor based on the amount of torque he needs, or at the very least trying to verify that the motor he is looking at is more than enough for the task.
Well, post links to a few of the datasheets he is considering, and we'll see if we can help. :smile:
 
berkeman said:
Well, post links to a few of the datasheets he is considering, and we'll see if we can help. :smile:
Sorry, could've sworn I put the link in the last post. My mistake.

http://www.newmarksystems.com/rotary-positioners/rm-8-motorized-rotary-stage/
Also, the thin disk being rotated is 6061 aluminum, 1/4" thick, 15" radius, and he wants it to turn 40 degrees over a period of 3.5 seconds.
 

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