The construction started from the chassis. Romulo has 4 wheels, the front ones are motorized and the back ones are freely steering and act as a pivot point.
The driving wheels are 80mm (3.15") in diameter and are made of rubber, they have good traction on the surface where the robot will work. For the motors, i used a pair of micromotors HV155.12.90 that i already have from another project. They have a torque of 25Ncm (2.21 lb-in), which is perfect (if not too much) for a robot of this size.
For the chassis, i used two angular aluminum profile, as you can see in the photo below.
And here you can see the very engineering way to couple motor and wheel:
And the chassis finally completed
Note that i used two "pivoting wheels" instead of ball casters, and this was a very bad idea. During maneuvers and change of direction, the pivoting wheels need space to rotate and get in the new position. This creates a small load variation on the motor and, since Romulo use an open-loop control system, affect the result of the maneuvers.
The solution could be to use ball caster or Omni-wheel.
You can even see in the photos the two sliding guides for the carriage and the two screws for the line sensor.
The next log will cover the big part of this project: the carriage, the fork and the lift system.