# Force needed to rotate a drum

1. May 20, 2017

### PatPat

I need to make sure that my drum which is connected to a shaft and with load of 30kg is able to rotate at 6500rpm.

mass of drum : 15kg, diameter 0.6m, length, 0.6m
mass of shaft : 11kg, length = 1m, diameter, 0.043m
desired speed : 6500rpm in 30minutes.

How can I determine my motor power that can turn my system? Can someone guide me with my problem?

2. May 20, 2017

### Staff: Mentor

Welcome to the PF.

That's a pretty fast rotational speed for that mass. What is the application? How are you ensuring a balanced system so that vibration does not tear it apart?

What is your background in mechanical design? Have you done this sort of project in the past?

3. May 20, 2017

### PatPat

Thank youu!

Its for my engineering design project . A high rotational speed drum to dry food. We are working in a group and we just need to create a simulation. Not the actual thing. I'm not sure about the balancing stuff as we're not stressed on such issue.

My part was to design the shaft for the drum dryer (the most important thing is to determine the shaft's diameter), to determine the mass of the drum and shaft and how many torque is required in order to rotate these three to 6500rpm.

4. May 20, 2017

### PatPat

I'm not sure if my diameter calculation is even correct, but we're using SS304 as the material. And I calculated roughly about 43mm diameter for the shaft. 1 meter long.

This is my first time working for such project.

5. May 20, 2017

### Staff: Mentor

Well, at that rotational speed, designing for stability is going to be a major part of the project. You will see it in simulation if you do a good enough simulation -- the stresses on the bearings and drum structure will tear the apparatus apart. Whose idea is the 6500 RPM? Is it a design requirement from the instructor for the project? Or is is a number just thrown out there by the students in response to a more basic problem statement.

Do you know what real-world designs use for centrifugal food drying?

6. May 20, 2017

### PatPat

Yeah it's the design requirement set by our lecturer. I'm not sure myself about those kind of stresses, as I have very low exposure to real life design and application.

However, just IF we're to ignore the balancing part, can you please give me a jump start to calculate for the shaft's diameter?

7. May 20, 2017

### Staff: Mentor

Sorry, I'm not comfortable ignoring the balancing issue. That will cause you to use a much bigger diameter shaft and drum structure. Could you please run this question by your instructor?

And see if you can find out what RPM is used by typical centrifugal food dryers like these:

I could see maybe 600 RPM withe a moderate amount of balancing effort, but 6500 RPM seems way too difficult to me. But others here may have other opinions...

8. May 20, 2017

### Staff: Mentor

9. May 20, 2017

### PatPat

But lets just assume that my instructor give a what you would say a recommended rpm. Can ya guide me on how to design the diameter? Which way should I start looking at.

10. May 20, 2017

### Dr.D

Rather than shaft mount this system, have you considered using multiple roller supports? This will take an unbalanced load much more easily than a shaft in bending.