Specifying Motors - RPM??

First LAW of Thermodynamics: Energy is not created or destroyed.

Power is energy per unit time.

Therefore the horsepower throughout your system is always the same, minus losses to friction, of course. Those losses turn to heat.

T = hp x 5252 ÷ rpm, with T in ft∙lb

So as the speed goes down T goes up in the same ratio. Always.



Understood, but what if the drive sprocket is much smaller than the drive roller that it's connected to? I know the RPM is the same, but when I'm calculating Torque, do I go by the drive sprocket or the drive roller?
 
you must first figure the torque required to move the load then figure what speed to want to move at.
Work back from their, sprocket size, gear reduction and so on.
I would try to size the motor to run close to 1800 rpm 4 pole motor as possible this will make the motor a standard motor then select the HP based on the calculation from the total reduction. I would add a little buffer and oversize the motor a little.
then use a good quality vfd sized to the motor.
 
Understood, but what if the drive sprocket is much smaller than the drive roller that it's connected to? I know the RPM is the same, but when I'm calculating Torque, do I go by the drive sprocket or the drive roller?

Perhaps the attached will help. Torque on any one shaft, such as the headshaft, is unchanging.

Ignoring friction, power is unchanging throughout the system. (First Law)
 
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Specifying Motors - Over powered for application

I have a question regarding some calculations I'm doing...

I find that most of our motors are around 1/2HP, so for some applications we may install one and gear it down to fit our needs.

What I have a question regarding, is how much over on torque or speed is acceptable. I can run the numbers sometimes and get 100% speed match, but way over on torque, or 100% on torque and high on speed. I would average the two and go in the middle of each as long as the application will work with it.

Obviously this is a improper motor selected for the application, I'm just curious what is considered normal values.




Thank you!
 

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