Most parts were bought on eBay.
It is controlled by Arduino board with very simple algorithm.
3 to 6 volts motors are used for moving. H-Bridge motor driver on HG7881 - a board controlling motors.
Base was made from plastic kitchen board - soft enough to be drilled, sawn and cut without much efforts.
Lithium battery (with solar cell) gives 5 volts and allows to work the robot about one hour.
Step-up circuit provides 12 volts to a turbine which collects dust. This circuit is made using standard design of MC34063 and induction.
Too tall - more than 12 centimeters (should be 11 cm maximum to go under a sofa).
Too slow - gear mounted on motors has too high ratio.
Other cons can be fixed:
thin bumper, simple algorithm for moving, no sensor on getting stuck.