Slewing Drives are a lower-cost alternative to robot rotary platforms that trades precision for cost while still being able to support a lot of weight.

That is, it's a composite solution:

• The slewing drive that can take a 100 lb off-axis load, with a high gear ratio, but not too wide in diameter as to be excessively huge or heavy. It uses a worm gear.
• An extra gear box to up the gear ratio even further
• A beefy ClearPath motor popular in robotics

The company that manufactures it is called Cone Drive. The STEP file couldn't download so I am modeling it off 2D drawings to plug it into the virtual assembly.