# Shaft torque requirement (should be simple)

• Seraph042
In summary, the conversation revolves around a design for a device that requires a certain amount of torque to rotate a shaft with a diameter and length, and a plate attached at the end. The goal is to rotate the shaft at 100 RPM using a motor, but there is uncertainty about the necessary torque and how to calculate it. Newton's 1st law is mentioned as a reference for constant speed motion, and there is discussion about losses and bearing friction. Ultimately, the conversation leads to the conclusion that more information is needed, particularly about the radial load and time constraints, in order to accurately estimate the necessary torque for this device.
Seraph042
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!

#### Attachments

• shaft holder.PNG
261 bytes · Views: 425
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.

## What is shaft torque requirement?

Shaft torque requirement refers to the amount of rotational force that is needed to move an object or system connected to a shaft. It is typically measured in units of Newton-meters (Nm) or foot-pounds (ft-lb).

## How is shaft torque requirement calculated?

The shaft torque requirement is calculated by multiplying the force needed to move the object by the distance from the center of rotation to the point where the force is applied. This can be represented by the equation T = F x D, where T is the torque, F is the force, and D is the distance.

## What factors affect shaft torque requirement?

The main factors that affect shaft torque requirement include the weight and size of the object, the friction between the shaft and the object, and the speed at which the shaft is rotating.

## How is shaft torque requirement tested?

Shaft torque requirement can be tested using a torque wrench or a dynamometer. These tools measure the amount of force needed to rotate the shaft and can provide an accurate measurement of the torque requirement.

## Why is it important to determine the shaft torque requirement?

Knowing the shaft torque requirement is crucial in designing and operating mechanical systems. It ensures that the appropriate amount of power is applied to the shaft and that the system can function properly without any failures or damage.

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