Looking for Definition of Rotor WR^2
Looking for Definition of Rotor WR^2
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Could anyone help me with the Definition of rotor WR^2
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Looking for Definition of Rotor WR^2
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RE: Looking for Definition of Rotor WR^2
Don
Kansas City
RE: Looking for Definition of Rotor WR^2
JRaef.com
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Looking for Definition of Rotor WR^2
RE: Looking for Definition of Rotor WR^2
Now I can be even nerdier when correcting people in the future!
JRaef.com
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Looking for Definition of Rotor WR^2
RE: Looking for Definition of Rotor WR^2
RE: Looking for Definition of Rotor WR^2
The reason you want to know moment of inertia is to be able to calculate the relationship between torque and angular acceleration: T = J * alpha.
In typical SI units, you get J(kg-m2)*alpha(sec^-2) =T(kg-m^2-sec^-2) = T (N-m), so no conversion factors are necessary.
In typical English units, you get J(lb-in-sec^2)*alpha(sec^-2) = T (lb-in), and again, no conversion factors are necessary.
But you must be really careful if you start using expressions for MOI like those above. You will need a conversion factor of 1/g (g=32.2 ft/sec^2) in the T=J*alpha equation if you use W*K^2 for moment of inertia. I've seen people get very wacky results if they leave that out.
People also often screw up if they use non-official units of "pounds-mass" or "kilograms-force" as they try to convert between SI and English. Again, they are usually off by a factor of "g" if they are not careful when they do this.
Curt Wilson
Delta Tau Data Systems
RE: Looking for Definition of Rotor WR^2
A pound is a unit of force, paralleled by the "newton" in metric.
1 lb = 1 slug-ft/s^2
As long as you use slugs for mass, feet for length and pounds for force, you can use all of the same simple physical formulas (like F = ma, etc.) as in metric without having to include a conversion factor. You're better off avoiding lbm and kgf entirely.
Don
Kansas City
RE: Looking for Definition of Rotor WR^2
RE: Looking for Definition of Rotor WR^2
RE: Looking for Definition of Rotor WR^2
Wk2 is a particular “simplified” constant for moment of inertia.
It has “weight” instead of “mass” and it is used on the expression:
t = Wk2 (rpmf - rpmi)/(308*Tavg)]
t = accelerating time in seconds
rpmf = final rotating speed in revolutions per minute
rpmi = initial rotating speed in revolutions per minute (normally zero at stand still)
Tavg = Average accelerating torque in Lb*Ft; the Motor torque minus The Load Torque.
By the other hand, in the general expression of mechanics; T = j*alpha
"j" is given as a “mass = weight/g “ times radius of gyration squared.
“g” is the gravity acceleration in length per seconds squared
"T" is the torque applied in force times distance
"Alpha" is the angular acceleration in rad/sec2
The units must be consistent for the selected system of measurement; MKS, cgs, English Imperial, etc.
RE: Looking for Definition of Rotor WR^2