pic: Planitary Transmission

[Alan Anderson]

Originally Posted by Paul Copioli

1. You do not get ANY added output torque from the ring gear motor ... zero, nada, nothing. The ring gear has to react against the input torque of the sun gear and adds nothing to the output torque.
...
4. When designing your gear ratio's, there are three basic areas that the CCT gives you: Ring gear in reverse, ring gear at 0, and ring gear forward. Design your normal operating conditions at ring gear at 0 speed.

It looks like Alex has designed his system "inside out" from the way you expect. If I'm reading the drawing correctly, the dual CIMs drive the ring gear, and the "variable" part is due to rotating the sun gear.