simple car

If you put bigger spacers on the wheel axles, the car will turn.
V.1:
https://www.youtube.com/shorts/_etvWDl4Rwo
V.2:
https://www.youtube.com/shorts/VI8FHopRNgM

If you put the right spacers on the wheel axles, the car will run straight with a fixed axle.
V.1:
https://www.youtube.com/shorts/11LMcrQRAO4
V.2:
https://www.youtube.com/shorts/w3Z9VaIpQh8

Spacers of different sizes are used for the tolerances of sticks.

The 3V motor has higher torque and speed, so it is recommended for use.
If you want the car to run slower, you can use 1.5V. However, the disadvantage is that it stops when it hits an object and there isn't enough torque to turn.

In Version 2:
The base is thicker by 3mm.
Gear for a motor with 1.5mm axel
The hight of the square is 6 and 7mm for the smaller motor.