Normally I've always used the L293D chip to drive my motors, but for a new project I am working on I will be using motors that I'll operate between 2.5 – 3.5V and I intend to power them using a single 3.7V LiPo battery.
I would obviously be way out of spec for the L293D for both VCC1 and VCC2, so I am wondering what another good option would be to drive these motors at a very low cost.
I will be using an Arduino Pro Mini (3.3V version) to provide the necessary logic signals.
EDIT: I would like two of these (or similar, perhaps of slightly higher quality) motors on my robot and I would like to be able to drive each independently forward or backward. Pulse width modulation to enable speed control of the motors would be really great, but not necessary. The reason I am going for these motors is because I would like my robot to be powered by a cheap and light power source, and 1 cell LiPos are the lowest cost solution I can find. I would consider 3x AAA batteries, but doesn't seem like they'll comfortably meet the voltage spec for the L293D.
Best Answer
If your motors draw less than 800mA each then an L9110S bridge driver should be sufficient. Boards with a pair of these drivers on them commonly sell on eBay for under $2 each (with free shipping, how do they do it?).
However if your motors are the typical type used in toys (eg. Tamiya 980112M) then they may draw over 2A, which is too much for the L9110. In that case it may be better to make a bridge out of discrete transistors, preferably MOSFETS as they have built in flyback diodes and are generally more efficient. If you buy in bulk the price should be competitive, though the total build costs may not be (what is your time worth?).
So before you make a decision, get a sample of the motor you want to use and test it. If the stall current is less than 800mA at 3V (armature resistance of 4Ω or higher) then use the L9110S. If it is much higher then consider building discrete FET bridges or get less power hungry motors (maybe they cost a little more, but the total cost could be less!).