moments of inertia

[mir]

Hi.
I have to find the torque I need to turn an object as in rotation.jpg (see rotation arrow)

question 1:
I thought I'd take the time of baricentro izz inertia for the calculation of the torque needed to the engine... Say it's the right one?

Question 2:
pair = x acc. angol.
i = moment of inertia
acc. angol. = but how do I establish this value? I want to turn the system to 30 rpm... do I have to determine how quickly I want to achieve that speed?

thanks for the help
♪

 

[godevolution]

Hi, mir,
the angular acceleration is in the transient of acceleration and braking.
at regime (at 30rpm) acceleration is nothing, therefore also inertia.
to calculate the initial inertia you have to decide how quickly you want to reach the speed of regime.
to calculate acceleration you can do so
initial speed = 0
final speed = 30 rpm
speed = 30rpm - 0 = 30rpm = 2*pigreco*30 = angle speed
t = you choose in how many seconds
Angle acceleration= angle speed / t

as you can see, the closer to zero, the more angular acceleration tends to infinity and consequently also the pair of inertia (pair of inertia= moment of inertia * angular acceleration). this for example is why on a car that goes from 0 to 100 in a short time you stick to the seat, while in one that goes from 0 to 100 in a long time, you don't even notice.

to simplify your calculation according to me you can disassemble your structure in two disks (to easily find inertia formulas for disks) and in a dotted mass that is located at distance r (the distance from the center of the disk to the center of an astina) from the z axis that sums up all the mass of the rods.

I hope I have been helpful and I have not made mistakes