Crucially important: does "control" mean "simple on/off"? "variable speed"? And, if the latter, do you want to control the speed of the motors individually? Or will they all be running at the same speed?
from my experience so far with this motor, there's not much variability even possible. I would rather have them going at full speed and off than any control speed.
I've used the 74HC259 latching multiplex chips for a lot of individual controls. Each chip can control 8 outputs. You would still need a transistor/resistor for each motor.
that relay board seems a little heavy duty for 3V at 90mA.
Really. This would be a good candidate for driving by a ULN2003 or ULN2803.
For the logic part, any old common shift register (like the 74HC595) would be fine.
If you don't happen to have any of those parts already, the TPIC6595 would be a good choice, too. It's also easier, because there's only one chip per 8 motors, and similar in cost on the hobby market. So, if you (have to) buy new parts for this project, it's arguably better.
If you wind up using ULN2x03s, take note of the fact that, at 90mA, their outputs will be at about 1V, because they have bipolar output transistors, not FETs. You'll need to adjust the voltage of the positive supply to compensate for that.
I have got my parts now and i'm assembling this little project with glee.
I'm a bit stuck on a tech issue.
The Spec sheet for the 74HC595 has confused me a bit and now i'm trying to figure out the best way to feed 3V 90mA to each output of the IC on command.
I'm assuming the best thing is to use a bunch of NPN's or a transistor array but i'm not sure which one(s).
A) How do i know/calculate what the Amperage coming from each of the 74HC595 pins? Is it determined on how many are on(ie=HIGH) at any one time?
B) How do i regulate the the Amperage and be sure that when a pin is on/HIGH, it will be set to 3V@90mA
Could someone point me in the right direction please?
I'm assuming the best thing is to use a bunch of NPN's or a transistor array
Yup. Using a ULN2003 or ULN2803 is easiest and (at least close to) cheapest. But note that it's only good for about 5 continuous 90mA loads per chip, due to the amount of heat it generates.
You don't need to calculate amperage for the HC595: the transistor (array) will do all the heavy lifting.
There are a couple of ways to get your motor power supply. If you have a hefty 5V supply, you can use two diodes in series between the supply and the motors to drop the voltage down to about 3.6V. The ULN2003 loses about .7-.8V, so it'll be just slightly below "maximum vibes" (and the motors will probably last a little longer as a result). If you do one diode pair for each 5 or 6 motors (to keep the per-diode current down), you can use dirt-cheap 1N400x diodes for the job.
Another alternative is to buy or build a variable power supply, but that's a little tricky for a newbie, because you need one good for at least 4A to spin all the motors at once.
