How to improve robot motors controllability

Hi all,

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...) ?

Thanks ALe

The TB6612FNG motor driver can control up to two DC motors at a constant current of 1.2A

and motor by separate four AA battery (so 6V).

I doubt that your AA batteries are up to the task of supplying 1.2A, let alone 2.4A for two motors. Adding more current capability seems like the first thing to do.

The no load current required by your motors is nearly 0.4A. The stall current is 2A.

I think you'd have much better response with a higher battery voltage.

The robots I have built recently have almost the same motors as yours. See one HERE:

I use 6 AA batteries for 7.2V with NiMH rechargeables. They will run 2 to 3 hours on a charge, doing collision avoidance. But I do see that there is very little torque with 1/2 duty cycle.

terryking228 is correct. In my experience you need 6 NiMH cells for good motor control.
Recently I changed to a pair Li 18650 cells for more punch.
18650 cell holders used to be hard to find, but are now available cheap on eBay and elsewhere.

Note that the 18650 cells have builtin protective circuits and are safer than the pure Li cells used for hobby planes & quadcopters which need very large currents.