It's not actually a question. I have learned a long time ago another another technique to animate a perfect circle and I'd like to share here.
1. Add a curve>circle and make it to your desired position and size.
continuing...
2. Select the object you want to animate and then the curve and hit Ctrl+P then choose "Follow Path"
3. Tweak the desired amount of frames in the curve properties.
4. The object should already moving but rotating as it follows the path, so you can lock its rotation with a "limit rotation" constraint.
