Vimeo member geco campos provides an overview of the Opteka FFR-900 Shoulder rig that offers a motorized Follow Focus and Motorized Zoom feature. Each handle up front controls one of the motorized units, and variable speeds can be dialed right from the handles if you wish to zoom/focus slower or faster.
The motors spin the focus/zoom rings through a belt system - no lens gears required. My guess is you should be using a lens that has a smooth and easy to rotate focus or zoom ring. The rear holds a master controller that can be used to operate the motors when the shoulder rig is tripod mounted. The motors are powered by an LP-E6 battery (generic LP-E6 battery + charger included), and can be found via eBay (click here).
Opteka FFR-900 DSLR Remote Motorized Follow Focus Zoom Control System
For USA residents, the FFR-900 is also available via Amazon (found here)