Ok I have some questions that need answer:
1) I read on the web what is inertia but never found how to calculate it.
2) If I have a motor with ball screw attach to the shaft. A metal sheet that
weight 100 pound is attach to the ball scew nut. How can I determine how
much torque the motor should deliver so I can have a angular speed of x
Dear Réginald Jean Louis:
inertia = mass.
You need to know how much torque the ball screw requires to deliver a force
along the screw's axis (assuming the screw is vertical).
Basically, we need a little more information...
David A. Smith
Ignoring moment of inertia, let us suppose that you wish to lift a
mass of 46 kg at a known rate (V specify it in meters/sec).
If you specified a motor capable of providing twice this power, you
would have an estimate of the power required from the motor, which is
46 X 9.81 x V (m/s) X 2 =
motor power in watts / 746 =
nominal motor horse power
In basic terms, inertia is an indication of a certain body's resistance to
rotate around a certain axis. Therefore it not only depends on the object's
mass but also it's geometry (mass distribution).
How do we calculate it? Being "I" the inertia of a body, "In" the the n-th
body's element's inertia and r the distance from the rotation axis to that
I = sum( In*(r^2) )
so, if a certain body is formed by 3 elements (inertia from body 1, 2 and 3
= I1, I2, I3) which are distanced from the axis of rotation (r1, r2, r3),
then that body's inertia should be:
I = I1*r1*r1 + I2*r2*r2 + I3*r3*r3
For mor information you can look at
any book on newtonian mechanics.
Well, being "w" the angular velocity, "a" the angular acceleration and "t"
the time, then we have:
w = a*t
And being "T" the applied torque, "I" the body's inertia and "a" the angular
acceleration, we have:
T = I*a
Solving the torque equation in order of "a" and replacing it in the angular
speed equation, we end up with:
w = (T/I)*t
...which says that if there is any torque applied on that body (the body's
inertia is always nonzero), it is only a matter of time before that system
reaches the wanted angular velocity.
Of course the problem isn't as simple as that. But without any additional
knowledge of the motor in question (structural resistance?), that is the
only thing that can be calculated, which isn't much.
So, as the parent post said:
Take care and hope this helps
Dear rui maciel:
"rui maciel" wrote in
message news:407aa41f$0$25979$ email@example.com...
Correct, however the OP did distinguish between inertia and moment of
inertia. You may have been correct that he/she did not know the
difference. And it is unusual for the sleeve of a ball screw setup to be
rotating... so moment of inertia wouldn't really apply.
David A. Smith