H-Bridge and PWM improvements/mistakes

So what kind of bridge would you recomend?

I'm using 2 Brushed DC Motors

Motor details:

  • Operating Voltage: 3V ~ 6V DC
  • Recommended Operating Voltage: about 3 to 6V DC
  • Load Current: 70mA (250mA MAX)
  • No-load Speed: 1:48 (3V)

IO pins 2,3 are connected to H-Bridge inputs A1, A2,
IO pins 4,5 are connected to H-Bridge inputs A3, A4
H-Bridge outputs
Y1,Y2 connected to left DC motor
Y3,Y4 connected to right DC motor

5V arduino is connected to H-Bridge Vcc1 for logic
6V battery connected to Vcc2 for power supply

The spec sheet at

says:

"The L293D is designed to provide bidirectional drive currents of up to 600-mA
at voltages from 4.5 V to 36 V."

What do you mean that it loses everything up to about 3V?