crank flashlight from homemade motor

I was hoping to attach a photo, but since i am not seeing that option, i will tell you that i also built a gear box to increase the power of the crank

(16 teeth to 30 teeth) x 3 if that makes sense

I am not given the rating of the motor or the bulb that you are trying to glow so I cant help you with calculaion. But here is a simple way to do it. All you need is a multimeter.

Power the motor with a 9V battery and make it run. Now use a multimeter to measure the voltage across the motor and the current drawn by it. Say for example the motor is consuming 9V with 600mA current running at 200rpm. This means if we are able to rotate the motor manually (with crank shaft) at 200rpm it will acts as a generator and can power a load (your light bulb) with 9V and 600mA current. So you can test you load with a power supply unit (or read spec sheet) to check how much current it will consume at which voltage level.

This is a crude way of doing it and numbers will not be accurate but should give you a rough idea. I would suggest you to connect a multimeter and to the motor terminals and measure the voltage as you roate it with crank shaft. This voltage value should give you a rough idea on how to proceed 

Hope this helps