# Appropriate bearing to spin a dove prism?

I want to spin a dove prism (image rotating prism) around it's long axis at a controlled rate (100 to 300 RPM). The purpose is to get a de-rotated image of a spinning object (by looking through the prism).

The prism is small and light - about 20x20x150 millimeters and maybe 0.1 kg.

My idea is to mount the prism inside a spinning bearing. I tried an inexpensive "pillow block bearing" (20) and mounting the prism inside, but that didn't work well: (a) The friction needed to turn the bearing was much higher than I wanted - I want it to spin freely (for example, if I give it a spin with my fingers, I'd like it to keep spinning for a while). I was driving the rotation with a small DC motor with a belt (controlling motor speed with a knob). The friction was a problem. (b) The axis of rotation didn't seem to be as constrained as I'd like - I want it to really just spin in one single axis that doesn't move around, so the view through the prism stays centered on a fixed point (assuming the prism is properly aligned with the bearing - I'm going to 3D print a fixture to hold it in place). Can I get a recommendation for the appropriate type of bearing for this? (Or, some other way to accomplish what I'm trying to do?) It would be nice if it's not expensive (<100).

• Although not relevant to the question, I would like to understand more how you are planning to "get a de-rotated image of a spinning object (by looking through the prism)." – NMech Mar 27 at 4:54
• @NMech A dove prism rotates an image by 2 degrees for every degree you rotate it. So if you rotate it in the opposite direction at half the spin rate of the thing you're looking at, you'll see a stationary view. – nerdfever.com Mar 27 at 14:48