Two wheeled car

https://youtu.be/mYVD8y65sYI

A two wheeled car, exploring the room on its own. Two increadibly cheap steppermotors 28BYJ take care of the action, controlled by an Arduino Nano and two ULN2003 ic's. It is powered by three AA batteries (4,5 V) placed as weight at the bottom of the chassis. The chassis has a hole for an on-off switch.
On the pcb is room for additional in- and outputs. Make your own unusual robot platform.
To be printed without supports.
An example Arduino sketch:

//NanoFull step mode
//512 >> 360 degrees 1.4 step/degree
int Pin0 = 9; int Pin1 = 10; int Pin2 = 11; int Pin3 = 12;
int Pin4 = 2; int Pin5 = 3; int Pin6 = 4; int Pin7 = 5;

int t=3;
void setup()
{
pinMode(Pin0, OUTPUT); pinMode(Pin1, OUTPUT); pinMode(Pin2, OUTPUT); pinMode(Pin3, OUTPUT);
pinMode(Pin4, OUTPUT); pinMode(Pin5, OUTPUT); pinMode(Pin6, OUTPUT); pinMode(Pin7, OUTPUT);
}
void loop()
{
//around axis
for(int x=0; x