# Need help calculating torque required

1. Sep 18, 2015

### Usman Maqsood

Hello! I am an electrical engineer and have taken on a task to design a rotating wooden column. See attached image of the column.

The requirements are to spin the column 360 degrees in 5 steps of 72 degrees each. The material used is wood.

I know what I need to do in order to get it to spin (stepper motor, gear, shaft, bearing etc). How fast does the column need to spin? Not fast. The stepper motor can be stepped however fast the design needs to be (up to a limit).

The issue: I don't know how much torque is needed to spin the column. This seems to be a slightly complex problem which I don't have the right background to answer.

The torque estimation will help me figure out what size motor i can use.

So, I would like to be pointed in the right direction to calculate the torque (internet references, reading materials, actual weight measurements etc).

Thanks for looking!

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2. Sep 19, 2015

### Baluncore

Welcome to PF.
If it is rotating about the vertical axis then very little torque will be needed.
You must accelerate it, then decelerate it. So it all depends on how quickly you need to move it.

You will need some idea of the rotating mass and the radius since moment of inertia is important.
https://en.wikipedia.org/wiki/Moment_of_inertia

3. Sep 19, 2015

### Nidum

Tie a piece of string to largest radius point of whatever is moving . Arrange string horizontally and tangentially to circle of motion . Take string over a simple pulley and then vertically down .

By trial find a weight which when tied to bottom of string and released starts column moving at required rate .

Option: take several string turns around actual column and do same thing but timing the turns .

Last edited: Sep 19, 2015