Equivelant moment of inertia

3 comments

Rate

Alun1986 Participant Join Date: Jun 2008 Posts: 3	Equivelant moment of inertia 06/17/2008 9:08 AM
	A speed reducing gearbox has a ratio of 15:1, an input rotor with a moment of interia of 35 kg m(squared) and output roto with a moment of interia of 95 kg m(squared). What is the equivelant moment of interia if the output rotates at 700 RPM? Can anyone offer any help, I don't have a clue how to work this question out!!!!!!!!!
	Register to Reply

Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

These comments received enough positive votes to make them "good answers".

Bill Guru Join Date: Dec 2005 Location: Clemson, South Carolina Posts: 1722 Good Answers: 18	#1 Re: Equivelant moment of inertia 06/17/2008 4:11 PM
	Are you asking about the reflected moment of inertia of the output rotor through the gearbox to the input? Ideally (which isn't real), the apparent mass moment of inertia at the input is 1/15 of its actual value, but moments of inertias of gearbox components have to be considered too. The speed of the output rotor doesn't change any mass' moment of inertia, but angular momentum changes with angular velocity. This help? __________________ We have met the enemy and he is us . . . Walt Kelly
	Register to Reply

Stirling Stan Guru Join Date: Nov 2006 Location: KnoxTN Posts: 1485 Good Answers: 6	#2 Re: Equivelant moment of inertia 06/17/2008 11:12 PM
	"output roto with a moment of interia of 95 kg m(squared). What is the equivelant moment of interia if the output rotates at 700 RPM?" See Wikipedia for "Moment of Inertia" which is a summation of the distance r^2 x m of each individual particle of mass. The momentum of the rotating mass is a gray horse of another color (grey?) __________________ Do Nothing Simply When a Way Can be Found to Make it Complex and Wonderful
	Register to Reply

bbei Commentator Join Date: Apr 2008 Location: Antwerp, Belgium Posts: 73 Good Answers: 8	#3 Re: Equivelant moment of inertia 06/18/2008 1:57 AM
	If you consider the mass moment of inertia being calculated relative to the output shaft then: 35 kgm² 15² + 95 kgm² = 7970 kgm² Mass moment of input shaft must be multiplied by the ratio squared and added to the mass moment of the output shaft. If considering the mass moment of inertia being calculated relative to the input shaft, then: 95 kgm² / 15² + 35 kgm² = 35.422 kg*m² So mass moment of inertia is dependant on which shaft you consider when having a gearbox with a ratio <>1 (most gearboxes do). In this case both values are related by a factor 15² (= 7970 / 35.422) Mass moment of inertia is independant of rotation speed. __________________ "It doesn't matter how beautiful your theory is, it doesn't matter how smart you are. If it doesn't agree with experiment, it's wrong." - Richard Phillips Feynman.
	Register to Reply Good Answer (Score 2)

These comments received enough positive votes to make them "good answers".

Copy to Clipboard

bbei (1); Bill (1); Stirling Stan (1)

	Got Something to Say?
	Ask a Question Start a Discussion

	Aerospace
	BioMech & BioMed
	Chemical & Material Science
	Civil Engineering
	Communications & Electronics
	Education and Engineering Careers
	Electrical Engineering
	General Discussion
	Instrumentation
	Manufacturing
	Mechanical Engineering
	New Technologies & Research
	Software & Programming
	Sustainable Engineering
	Transportation

	Site Directories
	Forum Directory Blog Directory User Group Directory RSS Feeds CR4 Rules of Conduct CR4 FAQ Site Glossary Who's Online (83 right now) Show Members