shaft RPM question

jcraft · Jun 6, 2011

Hi all,

Probably have a basic question here but have never calculated this so hopefully someone can lead the way and explain how to calculate. If you have a motor with 1/2" shaft rotating at 50 RPM and the 1/2" shaft is directly coupled to a 5" diameter fixture, then what will the RPM's be of the fixture itself. Thanks

keithkyll · Jun 6, 2011

50 rpm. Please add more details if it's rollers or gears. If rollers, then divide by ten. 5" disc will rotate at 5 RPM.

jcraft · Jun 6, 2011

It is a dc motor with a 1/2" shaft. The shaft will be directly coupledto a 5" diameter tool. the tool will have a 1/2" hole/keyway with a setscrew to lock motor shaft into tool.

bernie_carlton · Jun 6, 2011

If it's directly coupled then it should also be 50 RPM.

I believe keithkyll's request for clairification is because the direct coupled answer is obviously the same as the motor shaft itself. He was checking if maybe something was left out of the description.

jcraft · Jun 6, 2011

Bernie,
It doesn't seem like it would turn at the same RPM's. If I visualize that correctly if the 1/2" dia. motor shaft turns one rev. then the 5" diameter tool would turn way less than one rev..

keithkyll · Jun 6, 2011

RPM is Revolutions Per Minute. It will still be 50 RPM.
What you're probably thinking of is how fast the outer surface is moving. It's easier if we change to 60 RPM. That's one revolution per second. For the .5" shaft, it's .5 x Pi = 1.57 inches per second.
For the 5" wheel, it's 15.7 inches per second.
With that in mind, you can redo the math for 50 RPM.

Shortcut is 15.7 x 5/6

BryanG · Jun 6, 2011

Google - Linear speed and angular speed

Here's a couple to get you started:

http://www.youtube.com/watch?v=V1hva4OpKcs

http://mathsisinteresting.blogspot.com/2008/08/linear-angular-speed.html

jcraft · Jun 6, 2011

Makes sense, thanks guys!

ScottTheEngineer · Jun 6, 2011

If directly coupled implies there is no change in gear reduction then it will be 50RPM.
If your measuring say the length of paper coming out of a roller than that is measured in Length not RPM.

-damn, I just read Bernies answer. But I already typed this out so I'm posting anyway.

shooter · Jun 7, 2011

It is a DC DC DC motor so rpm is unknown.
and if it is a AC and it is a drilling also unknown.
but yes the RPM on direct coupled is same.
the outer speed is not obvious.

JeffKiper · Jun 7, 2011

shooter said:
It is a DC DC DC motor so rpm is unknown.
and if it is a AC and it is a drilling also unknown.
but yes the RPM on direct coupled is same.
the outer speed is not obvious.

Shooter why do you say it is unknown? He could be using a armature feedback or a flux vector drive. He may have a encoder feedback on this system we will not know without more details. It doesn't matter really he already has his answer.

shaft RPM question

jcraft

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jcraft

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