In total 2 prototypes were built, 1 by E (14y old), and 1 by B (11y old).

the first one rotates a lot and moves slowly. This may be excellent for thorough cleaning.

the second one moves fast and doesn't rotate.

The difference is in the weight balancing, in positioning the battery holder and motor,
and in the selection of the asymmetric load.

By choosing the position, you can physically 'program' the robot behavior.

Here is a video comparing the behavior of the 2 prototypes :