Andrew - First robot

Hi all! First robot ever, saying it's not great would be an euphemism, nevertheless I would be very glad to get some feedback from you.

How it works : two switches on the front, when it meets a wall, andrew goes backwards and turn, then turn the other direction and goes forward again (see videos)

Controller : Arduino Uno. Structure : Knex. Direction : two front wheels turned by a micro servo. Engine : DC motor (with some knex gears), linked with 2 rubber bands to the back wheel. Electronics used : 4 transistors, 4 diodes, 6 resistors (330ohms and 10kohms), 1 capacitor.

Two interesting problems I've met and solved (oh yeah!) :

1) Making the DC motor going backward without H-bridge or motor shield (because I didnt want to buy and wait for these)

--> I made myself an H-bridge, with 4 transistors (2222A) and 4 diodes, according to the drawing I found there : http://www.electronicsteacher.com/robotics/robotics-tutorial/advanced-robotics/controlling-dc-motors.php

I used 330 ohms resistors to connect the arduino pins to the transistors' bases. 10kohms didnt let enough current flow.

Note that the DC motor is powered separately, with what look like a 9V battery but is most probably much lower because it's rechargeable but I don't know the value...

2) The circuit worked perfectly with leds in place of the dc motor, but it went mad when the dc motor was plugged

--> Apparently the dc motor was causing EMI (Electromagnetic Interferences), I read a great article (http://www.thebox.myzen.co.uk/Workshop/Motors_1.html), put a capacitor of 560 nF in parallel with the dc motor, and all the problems went magically away.

Please tell me what you think, especially about the power, I read a lot of different things about how to power properly the motors and arduino and yet I'm not sure my way is correct, the possibility of frying the card scares me a bit :s

Next project : get an IR sensor, a motor shield, put two dc motor at the back and make the robot going around avoiding obstacles without stopping. Some advices about the shield?