I'm planning to make a micro/nano quadcopter and I've bought all major components so far. The only thing that I can't figure out are motor drivers. I was planning to use some kind of transistor to do that for me (motors are 3.7V @ 1.5A marked). So I was wondering if that is a good idea? No commercial drivers can fit since it needs to be lightweight and I have 4 motors that need to be driven separately.
You will need to make your own bi-directional discrete H bridge (if you want to drive propellers in both directions) or a half bridge if you want only one direction.
Don't get 2A transistors, get something like 8-10A rated MOSFETs and ensure your design can survive inductive loads and over-voltage spikes from the motors. Do the proper research into H bridge motor driving and see some example designs.
You can get "complementary" N and P Channel MOSFETs in nice little SOIC-8 packages or perhaps DIP-8 which are rated for the 8-10A I suggested. Use these to make nice compact motor drivers for each of your motors.
Make sure the transistors are "logic level gate drive" meaning they turn on/off with only 1-2 volts.
You are right that there are not many commercially available modules or packages easily purchasable for this use. You'll find there are some nice integrated ICs that can do what you want though, they are just large (usually 20+ pins) and will not fit well on your nano-copter design.
I expect you'll need to make a PCB to hold the driver.