Hi,
The basic parameter to look out for when driving
your motor should be the current.
1st you need to know that maximum current your
motor will draw out from power supply.
If you do not have datasheet,
you can use a lab power supply or multimeter to measure.
The power supply equipment current rating
should be higher than that of your motor.
If you don't know, just try.
Supply the motor with the recommended voltage.
Grab or lock the motor shaft.
By locking the shaft, you are forcing the motor to draw
the maximum possible current from the power supply.
Measure or note down this current rating.
This is the max current you could expect out of the motor.
Choose the transistor with a current rating more than
the motor max current.
Preferably 1.5 to 2 times accordingly to my own standard.
The same current would be flowing through the motor
and the transistor. A higher current rating of the transistor
is better as you can expect less heat to be generated.
Cons may be bigger in size and higher in price.
Transistor has many other parameter like breakdown voltage,
gate voltage, many many more etc....
However they are usually insignificant unless you are working on higher voltage.
Which is why on most transistor datasheet,
the first information you usually see would be the current rating,
followed by the breakdown voltage, and the pin out information.
As a beginner, the rest of the parameter you might just leave it out first.
Until you encounter circuit problem, you can take your time
to understand more about the other parameters of the transistor
that might make your circuit fail.
Learn as you hands-on along. This is the way it is.
I have a simple write up on my understanding
on using transistor as a switch.
Hope it helps you.
**broken link removed**
Best Regards,
Soing Boon