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Planetary Gears: How to rig for rigid body physics engine?
The following image shows a planetary gear mechanism under a rigid body physics simulation. All gears involved are under a hinge constraint, and the central red gear is also under a motor constraint. The cylinders are used as Object 2 for the corresponding constraints, and marked "passive".
What I need, however, is for the outer (yellow) gear to be stationary and the centers of the satellite gears (blue) to move around the center. But I can't figure out how to rig this correctly.
Can someone please nudge me in the right direction?
Thanks in advance.
You have already done the most part of the job.
Connect the gray cylinder (the bottom one) to each of the pink cylinder with a constraint of type hinge.
The created empties (empties added by the previous constraints) need to be aligned on the center of the system (Z axis) as the pink cylinders need to rotate around this axis
Set all the pink cylinders to active as they need to move
Set the yellow gear to pass

You have already done the most part of the job.
Connect the gray cylinder (the bottom one) to each of the pink cylinder with a constraint of type hinge.
The created empties (empties added by the previous constraints) need to be aligned on the center of the system (Z axis) as the pink cylinders need to rotate around this axis
Set all the pink cylinders to active as they need to move
Set the yellow gear to passive as it needs to stay in place
20180610 08:00:20 
I think your original solution was much better due to favourable gearing ratio of the yellow gear vs pink gear.
20180610 09:10:50