I'm implementing moving logic for my robot using Arduino DUE, Magician Chassis (http://www.homotix.it/catalogo/robotica-e-accessori-438/magician-chassis) and TB6612FNG motor control (https://www.sparkfun.com/products/9457). The DUE is powered by a 9V battery and motor by separate four AA battery (so 6V).
The system is working but the problem is that I cannot move my robot at low speed: if I set the PWM of two motors to a value less than 128-172 the motor has not enough torque to move the robot.
Probably I'm using too low cost component but by now I need to be able to move my robot with more precision so I'm ready to change some components.
What can I do to improve the situation (change motors, change motor control, increase the motor battery...) ?