I am trying to build a project that will involve 5 DC motors that are each 6v and range from 50-100 milli amps. All I want to do is have them run either on or off. I am not interested in changing the direction they spin, braking, etc. It was recommended to me that I use transistors to control these motors from an Arduino since most motor shields only have room for 2 motors. Transistors are still new to me and I was wondering if anyone had any ideas about what kind would be best to use, if they are in fact the right choice for the project.
For that quantity I'd recommend a ULN2803 or similar chip. Unless you're working in SMD, it's going to be a lot easier to wire up than discrete transistors.
I have a shield you can etch yourself here: http://hacking.majenko.co.uk/octal-darlington-shield - if you want PWM then you might want to adjust it slightly to use more PWM pins than it does at the moment.
So in terms of wiring one of those up could I for example have the ground of a 6v motor connected to pin 18 on the ULN2803, the ground on pin 9 running back to the battery pack and a digital pin on the Arduino writing HIGH or LOW connected to pin 1 on the ULN2803. I really appreciate your help.
For the ULN2803 you connect the power to the motor, then the motor to the ULN's drive pin (pin 18 for example). Pin 9 is then connected to ground, and pin 10 to the same power as the motor. It operates as low-side switching, and the extra power connection is for the back-emf diode.
Then you link pin 9 to the Arduino's ground, and pin 1 (the input to control to pin 18) to the digital IO pin.
Many thanks.