# I Finding Torque Without An Angular Acceleration (stepper motor)

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1. Mar 12, 2017

### Tyler

A friend of mine posed a question to me the other day and I can't seem to wrap my head around it.

He's working with an electric stepper motor to turn a large thin disk, but he can't be sure of the torque required because to find the torque he needs the moment of inertia and the angular acceleration. The moment of inertia is easy to find since he has all of the disk's dimensions, but the electric stepper motor is taking the thin disk from 0 to a near constant velocity and back down to zero almost instantaneously.

Is there some other way to find the torque/angular acceleration that I'm just not thinking of?

2. Mar 12, 2017

### Staff: Mentor

What does the datasheet for the stepper motor say for the available torque per step? How many degrees is each step? The steps are not "instantaneous" -- the datasheet should give some idea of the time per step that is advised (depends on drive voltage and current)...

3. Mar 12, 2017

### Tyler

Well, therein lies the catch. He's trying to pick a motor based on the amount of torque he needs, or at the very least trying to verify that the motor he is looking at is more than enough for the task.

4. Mar 12, 2017

### Staff: Mentor

Well, post links to a few of the datasheets he is considering, and we'll see if we can help.

5. Mar 12, 2017

### Tyler

Sorry, could've sworn I put the link in the last post. My mistake.

http://www.newmarksystems.com/rotary-positioners/rm-8-motorized-rotary-stage/
Also, the thin disk being rotated is 6061 aluminum, 1/4" thick, 15" radius, and he wants it to turn 40 degrees over a period of 3.5 seconds.