How can I apply two different rotations to the same Blender object?

Question

I'm trying to build an object with multiple gears. One of the gears is attached to a larger gear, so when the larger gear rotates the smaller gear moves too, around the center of the larger gear.

Simultaneously, the smaller gear is rotating as well - but its rotation is around its own center, independent of the larger gear.

So:

1. Larger gear rotates around its center
2. Smaller gear moves around the center of the larger gear with its rotation
3. Smaller gear is also rotating independently

I can get 1 and 2 by animating the larger gear's rotation and then grouping both gears, but I can't figure out how to get the smaller gear to rotate around its own axis as it's going around the larger gear.

Any ideas would be appreciated.

Answer 1

The key is parenting.

• Create the first gear and get it rotating.
• Create the second gear next to it and animate that one.
• Select the second gear then shift select the first gear and press ⎈ CtrlP and select Object.

Now as the first gear rotates, the second will follow it's rotation while keeping it's own rotation.

If you want the outer gear to rotate the opposite way to the inner gear you can place an empty at the same location as the inner gear and use a copy rotation constraint and set invert to have it rotate the opposite way, then parent the outer gear to the empty.

Here's a sample file
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