Previous in Forum: Piston Ovality - Single and Double Ovality   Next in Forum: ASME B31.3 - Section 304.3.3
Close
Close
Close
3 comments
Participant

Join Date: May 2009
Posts: 1

Power and Torque

05/08/2009 12:50 PM

I need to calculate the required power and torque to turn a solid metal wheel on a test bench.

A small wheel is used to turn the big metal wheel. What power and torque is needed to do this?

D=1220mm

d=200mm

N=100rpm

n=610rpm

W=2ton

Register to Reply
Pathfinder Tags: power torque
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.
Guru
United Kingdom - Member - Not a New Member Hobbies - Musician - New Member Hobbies - Fishing - New Member

Join Date: May 2006
Location: Reading, Berkshire, UK. Going under cover.
Posts: 9684
Good Answers: 467
#1

Re: power & Torque

05/08/2009 1:00 PM

Once it's turning with N=100rpm, power = torque = 0 (neglecting friction, which we must since you haven't told us anything about it).

Realistically, you need to say what run-up time you're looking for (which will probably be the most significant factor in the final torque figure), and give some estimate of the friction.

__________________
"Love justice, you who rule the world" - Dante Alighieri
Register to Reply
Guru
Brazil - Member - New Member Engineering Fields - Mechanical Engineering - New Member Hobbies - RC Aircraft - New Member Hobbies - Target Shooting - New Member Hobbies - Automotive Performance - Hey there... interested in exchanging information about car performance? Hobbies - DIY Welding - New Member

Join Date: Jan 2007
Location: Porto Alegre - RS - Brazil 30deg01'39.73"S 51deg13'43.45"W
Posts: 831
Good Answers: 28
#2

Re: Power and Torque

05/08/2009 7:51 PM

What JohnDG means is that, if you need the speed to be constant, you're not going to spend energy except for compensate for the friction in the wheels bearings and between them. What is the bearings geometry, type, arrange? Maybe someone can give some tips and estimate it. Besides I agree that the speeding-up time would count with most of the required power installation: if you install a motor that is capable of accelerating the mass to the desired speed under a desired amount of time, it will easily maintain the speed with a lot less energy.

__________________
Humm... suspicious you are...
Register to Reply
Guru

Join Date: Sep 2007
Location: East Texas
Posts: 1386
Good Answers: 31
#3

Re: Power and Torque

05/09/2009 11:55 PM

A picture would be nice.

In terms of classical freshman physics it appears to be a very straight forward problem.

Given the change in rotational energy as ΔE= ½IΔω²

Where I= moment of inertia and ω=angular velocity.

By introducing the time component and referring to the definition of power as the rate of doing work then the rate change in energy would approximate the power required to accomplish that change.

ΔΕ/Δt= (½IΔω²)/Δt = Power

If you are going be accelerating your primary wheel with an acceleration wheel then the rate of acceleration will be limited by the force by which the acceleration wheel is pressed against the primary wheel and the coefficient of static friction of the wheels interface. This limiting friction force will define the torque that can be applied to the acceleration wheel before the wheels begin to "slip."

This same method can be used to estimate the power required to accelerate linear systems where the power required is the rate change of the linear kinetic energy(½mv²) of the system. One of the comparisons I have made is the power required to accelerate 1000kg of mass to 1/4 the speed of light in one year to the power that would be required to accelerate that same mass to the approximate heliocentric hyperbolic speed of the fastest human space probes in three days.

Gavilan

__________________
"The greater danger for most of us lies not in setting our aim too high and falling short; but in setting our aim too low, and achieving our mark." -- Michelangelo
Register to Reply
Register to Reply 3 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.
Copy to Clipboard

Users who posted comments:

bhrescobar (1); Gavilan (1); JohnDG (1)

Previous in Forum: Piston Ovality - Single and Double Ovality   Next in Forum: ASME B31.3 - Section 304.3.3
You might be interested in: Torque Tubes and Torque Arms, Torque Sensors

Advertisement