arduino + 2 steppers over 2 L293D do scrach

Hi all, I am making a small robot, stepper motors with two oki, of 3.7vy 6.8 ohm. and in driver L293D, the axes I have connected the wheels directly, 5v feed them. , In the air works fine, but when I put it on the floor of the wheels do scrach
thanks for all.

5v feed them.

Where do you get the 5v from? The Arduino 5v supply can not supply motor power, it can not supply that much current.