Here is another heavy duty robot that can take on a variety of tasks. The SDR 4WD All-terrain Robot from SuperDroid Robots comes with 120 RPM wheelchair motors and 13″ tiller tires. The robot is only 26 inches wide, so it should fit between standard doors.
The machine has a max payload of 250lbs. It has a top speed of 5mph. With the FLYSKY remote control, you can wirelessly control the robot.