# Rotating two things on the same axis

I'm working on a project where I want two separate shafts to be in the same place. Think of it like a clock where the hour and minute hands move independently. Also like a clock, I want the motors and gears tucked away in back.

With clocks, they use a kind of tube that slides over a shaft. Then the shaft and the tube can both be driven from the back and rotate independently.

Is there a name for this tube part? If I wanted it to be low-friction, is there a name for a part that includes bearings?

• maybe coaxial shafts or tube shaft .......... name for a part that includes bearings I don't see how this would have a specific name Jan 4 '19 at 1:49

It's called a sleeve bearing if you intend for the shafts to rotate relative to each other or a bushing if you intend for the shafts to move axially relative to each other. They generally look pretty much the same, and usually are, and people generally just use the term "bushing" for both, but there is technically a distinction.

You're probably going to have trouble getting power on and off the bushing unless you machine it to have some kind of gear teeth or something, and if you want the outer "shaft" to rotate relative to the chassis then you'll need a bearing for the outer shaft, too, so you'll wind up with bearing-sleeve bearing-inner shaft.

Getting power to or from the shaft is an open-ended question that is driven by your task, so please save any questions like that for Robotics Chat when you have sufficient reputation.