L293D driver DC motors need help to start rotating
The L2978D is a terrible motor driver (I really wish people wouldn't use it!). It is &quot;bipolar&quot; which means that both the high and low side switches of the H-bridge are Bipolar Junction Transistors. This means that you get about 1.4V voltage drop in total between the inputs and outputs.
To counter that you must provide at least 1.4V more than your motors need for them to operate properly.