Make sure the robot is designed with the base of the arm at the world origin. The Z axis (blue) should be up. The X axis (red) should be forward.

Make sure there is one Component for each moving section of the arm and the base.

Hide any internal components. This protects your design secrets and makes the file run smoother.

Export each component separately. Remove every component except the one to export, then click on the root of the project, right click, and save as mesh

Set the Format to OBJ.

Set the Unit Type to centimeters.

Export it to a folder on your computer.

Use the Undo to restore the deleted components and then repeat for each of the other components.