Shaft torque requirement (should be simple)

  • Thread starter Thread starter Seraph042
  • Start date Start date
  • Tags Tags
    Shaft Torque
Click For Summary

Discussion Overview

The discussion revolves around determining the torque requirement for rotating a shaft with an attached plate at a specified speed of 100 RPM. Participants explore the implications of torque in relation to acceleration, losses, and the characteristics of the motor selected for the application.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses uncertainty about how to calculate the torque needed for their shaft setup, mentioning attempts to use the polar moment of inertia.
  • Another participant argues that constant speed motion does not require force, questioning what force the device is acting against.
  • A participant suggests that the torque required is related to the acceleration of the shaft to 100 RPM.
  • It is noted that the torque needed to maintain angular velocity is equal to the losses, and the motor must be capable of overcoming these losses at 100 RPM.
  • One participant inquires about how to estimate the losses, indicating that the information provided is insufficient for a reliable estimate.
  • A participant mentions using a steel shaft and bearing and seeks guidance on determining the radial load based on the provided information.
  • Another participant points out that the largest torque requirement would occur during acceleration, while steady-state operation would only need to overcome losses.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the torque requirements, with multiple competing views on the factors influencing torque, including losses and acceleration. The discussion remains unresolved regarding the specific calculations needed.

Contextual Notes

Participants acknowledge limitations in the information provided, particularly regarding the estimation of losses and the need for additional parameters to make accurate calculations.

Seraph042
Messages
26
Reaction score
0
Hello,

I apologize if this question appears simple; it may be but I cannot find the answer in any of my textbooks.

I want to turn a shaft with a diameter, d, and length, L, which has a plate attached at the end, of diameter D.

I made up a side view of what I'm trying to illustrate in MSPaint as attached (shaft holder.png)

I need to be able to rotate this at the free end of the shaft at 100 RPM, and my plan is to attach a sprocket at that end, link it with a chain, and have another sprocket connected to a motor.

My question is, how much torque should I need to rotate this given the following parameters?

I'm not sure where to begin; I tried to analyze this as a problem with a circular shaft and a weight at the end, and also I've tried using the polar moment of inertia of the shaft but it's leading me nowhere!

please help!
 

Attachments

  • shaft holder.PNG
    shaft holder.PNG
    261 bytes · Views: 503
Engineering news on Phys.org
Sorry, but it is actually an impossible question. According to Newton's 1st law, constant speed motion requires no force.

We need to know what force this device is acting against.
 
Presumably the torque required to accelerate the shaft to 100 RPM

All I know is that I selected a cheap motor capable of providing 100 RPM for this design and my professor yelled at me for not including 'Torque considerations'

Am I misthinking this ?
 
The torque needed to maintain an angular velocity is equial to the losses. You need to make sure that the motor has this capability at 100rpm.

How you'd go about finding and quantifying the losses is another story.
 
What do I need to do in order to figure this out ?
 
There is no real way to even begin to estimate losses with the info posted. However they are likely to be small and insignificant.

Do you need it to accelerate to top speed in a given time?
 
The largest torque would come during acceleration. If you had some sort of time constraints then you could estimate these.

But at steady state,(like someone already stated) you only need to overcome your losses.
If you selected a motor that could run at 100rpm at no load, then it won't be able to do the same with losses. Maybe this is what your teacher was saying.
 

Similar threads

Torque calculations: Rotating vertical shaft
  • · Replies 5 ·
Replies
5
Views
5K
How Do You Calculate Deflection and Shear Stress in a Tapered Shaft?
  • · Replies 2 ·
Replies
2
Views
3K
What Torque is Needed for a Hydraulic Motor to Lift a 10 lb Box 20 Feet?
  • · Replies 9 ·
Replies
9
Views
2K
Help needed to solve a static analysis for the design of the Shaft for a Grinding Machine
  • · Replies 4 ·
Replies
4
Views
2K
Power, Rpm, Torque - Horsepower increase for my small engine
  • · Replies 4 ·
Replies
4
Views
4K
How to Measure Torque Required for motor to spin a rotating shaft?
  • · Replies 3 ·
Replies
3
Views
5K
How to spec a motor for this floor testing system?
  • · Replies 10 ·
Replies
10
Views
2K
Shaft Friction Control: Simple Solutions
  • · Replies 5 ·
Replies
5
Views
3K
Torque calculation for a new loading mechanism
  • · Replies 8 ·
Replies
8
Views
3K
What is the Required Torque for Moving a 20 kg Weight with a 10 cm Crank?
  • · Replies 5 ·
Replies
5
Views
3K