I am trying to build a robot with the Arduino Uno and the H-Bridge SN75441.
The robot has 2 1.5V rated motors. I set it up with this tuto: http://www.mlbelanger.com/arduino/ard-bot/
So the circuit is like this (I have just not plugged the Arduino Vin pin in the pin 8 of the chip):
As you can see, the H-Bridge only supports down to 4.5V for the motors. That is why I had to use a 5V power input (adapter 5v @ 1A) to power the motors, with PWM (80/255, giving a 1.5V normally) for regulating the power to 1.5V.
So here goes my problem. I have two cases:
one where the motors have no load, which means that the robot is in the air. The motors run at 1.5V @ 0.26A normally.
the second one which I have trouble with: it runs at 0.5V @ 0.145A. So the voltage dropped as the load increased. The robot doesnt advance and makes a kinda high-frequency noise. If I use 1.5V AA batteries connected directly to the motor, it runs well so the load is not the problem, but rather the PWM setup somehow.