I'm controlling 2 DC Motor's (link attached) using PWM. But, I noticed that when I'm smoothly reducing the speed of the motor and the duty cycle is approximately 25/30%, it stops moving..
I guess that's because the motor is not receiving enough voltage when I have a duty cycle inferior to 25/30% . However, can you tell me if the motor is already locked (duty cycle = 0) with a duty cycle between 1% and 25/30%, or it's just in neutral point (like the motor of a car when I don't shift into a gear)?
I'm asking this, because I want to use these motors to build a 'car', and if I want to turn right (for example) I'm reducing more quickly the speed of the motor on that side. If it lock's before it achieves DC=0%, the left motor will drag the right side of the car.. It would be important to know this, before I assemble the several parts.
When the duty cycle is greater that zero there will be current flowing through the motor, but just not enough to overcome friction and make the motor turn.
I think you will need to do some experimenting to find the point at which a motor will stop "free wheeling".
You do not state whether the motor is driving a mechanical load during your tests; if it is then the load may just be too great to permit motor rotation.
If the motor is mechanically disconnected from a load, then I feel there is something not quite right with either your motor or PWM drive system.
At all values greater than 0% there is FULL system voltage being pulsed to the motor. It is the duty cycle (ON time) of the PWM that determines the mean voltage applied to the motor, and hence the motor speed. So, even considering motor friction, anything greater than say 5% should be capable of driving a mechanically disconnected motor.