It's the main element to make the movement of the mechanism, tis is not necessary that works with fuel,... can work with other forms, it name is the..........
Its is necessary for the form and the support of the mechanism, if the mechanism doesn't have it, it's very difficult to carry up something... it name is.....
It is an elemnts to support the mechanism and work with the motor, with thah elements you can move from one side to another.....
It's a type of axle. You cannot see it because it is imaginary but support the wheels.