30:1 Micro Metal Polulu and Arduino Nano

Hi, i have a small robot with: - two DC Motors http://www.pololu.com/product/2212 - Arduino Nano - L293D H-Bridge - nrf24l01

I managed to command the robot from PC via nrf24l01, but after two or three commands the Arduino on the robot freeze. Commands are simple: 1 to go forward for 2 sec and stop, 0 for go backward for 2 sec and stop.

I put three 0.1 uF capactors like here: http://www.pololu.com/docs/0J15/9.

I have a 2 cell Li-Po 7.4V 1000mAh(25C) connected to a LM7805. Motors and Arduino are connected to the 5V output of the stabilizer and the nrf24 module to 3.3V Arduino output pin.

LM7805 maximum output current is 1.5A and motors eat 120mA without load. What could be the problem?

The stall current is the problem. Each motor briefly consumes the stall current when it starts up, and TWICE the stall current if it is suddenly reversed. From the Pololu page:

Key specs at 6 V: 1000 RPM and 120 mA free-run, 9 oz-in (0.6 kg-cm) and 1.6 A stall

Yes, so reversing both motors simultaneously will try to pull 6.4A if motors supplied from 6V.

The L293 H-bridge(*) will be limiting the voltage to the motor to about 2.5V BTW - you need to feed the H-bridge direct from the 7.4V LiPo (add a 5A fuse, note).

Keep the high current wiring away from the nRF24L01, BTW, and you'll probably need 10nF ceramic cap across each motor terminal pair to knock-down the RF noise.

(*) The L293 is a darlington bridge, so each high- and low-side driver loses 1.1 to 1.5V across it, which is very wasteful for a low-voltage motor.

The motors are not suddenly reversed. They stop and Arduino waits for next command.

Are you using input/output capacitors with the LM7805?

Only on output. I'll hookup one on the input to see the effect. What capacity should i use?

The datasheet for the exact regulator you have is the best guide (7805's are made by dozens of different manufacturers).