The robot cleans floor using vacuum produced by tiny computer cooler turbine. Automatically roaming in the room avoids furniture and walls. Assembled during weekend.

Step 1: Use Any MCU Controller and DC Motor Driver to Control the Robot

Any MCU with DC motor driver suit to control this robot. The robot is controlled by AVR Atmega48 with L293D motor driver which were assembled on the prototype board.
Because L293D warms pretty much an aluminium heat sink is mounted on it.
The 6 volts accumulator is used as a power supply.
L7805 5 volts regulator is to supply valid level power to the controller circuit.
This controller could have less contacts - this board was made to be used in other prototyping.
This ATMega MCU was programmed by BascomBasic.

Step 2: Step-up DC Power Converter

The step-up DC converter was assembled on the controller board because a computer cooler turbine requires 12 volts but the accumulator provides only 6 volts. The MC34063A chip was used. There are online calculators to define required component values (like this one).

Step 3: Reverse Side of the Controller Board

All connections were made by soldered wiring.
Resistor are to limit current between bumper contacts and MCU input pins.
The circuit is sort of "reverse engineered" by a soldered board (as I lost the original schema).

Step 4: Plastic Jar As a Cover Case

A plastic jar (or basket) is used as a cover case. Part of this will be used as bumpers.

Step 5: Assembling

The case from plastic jar defines the size of the robot. Draw the circuit in jar size and assemble all robot parts inside it.
For such work it's easy to use steel belt for wall mounting works.
Motors, gears and wheels are from toy car.
Computer cooler turbine is mounted on the cardboard box.

Step 6: Dustbin

A kitchen napkin made from nonwoven fabric is situated inside the cardboard box with the turbine. It is a dustbin. This fabric can be easy replaced.
Air with dust comes into the aperture in the bottom of the dustbin box and goes out through the fabric which collects dust.
A tiny wheel for furniture is mounted as a third supporting point.

Step 7: Bumpers

Bumpers are to define obstacles on the robot's way - like walls and furniture. The bumpers are cut direct in the case. Behind the bumper surfaces copper wires are mounted as bumper contacts. These contacts are connected to MCU input pins.

Step 8: The Robot in Action

In the video robot collects pretty much dust.
The attached program is written in Bascom Basic. It could be even shorter but this one contains extra code which avoid the robot be stack in corners for a room. The program was found among other versions, so I'm not sure it was latest one.