Arduino + simple DC motors? (4WD kit) I am trying to connect 4 small DC motors to Arduino, like those in the following image:


The specification for each of them is:


  Suggested Voltage: 3V DC;
  No Load Speed: 65 ± 10rpm;
  No Load Current: 125mA (170mA MAX).


But I have no useful knowledge in electronics to do so...  

I would be really thankful if anyone could explain me why it is so difficult to connect DC motors to Arduino (I've heard about problems with the magnetic field, but I don't really understand why); and possible point me to an easy (and cheap) solution. I am, of course, willing to study (not expecting a complete solution).  

I'm aware there are some shields for doing this kind of connection, but they are really expensive, and I've seen some people using only transistors or components like SN754410.

Thank you in advance! :-)
First you make 4 parallel H-Bridges, http://en.wikipedia.org/wiki/H_bridge then you attach it to an external powersource ( or attach directly to the battery to prevent burning your arduino )

Attach every up to a pin, making it high makes the motor running, you need 8 pins for this, eg pin 1 makes motor 1 go forward, pin 2 makes motor 1 go back and so.

This is by far the most practical solution, but it is the easiest, and can be done with 8 PNP and 8 NPN transistors.

If you don't know how transistors work i suggest https://www.youtube.com/watch?v=-td7YT-Pums collins lab, it is both educational and entertaining.