How to Determine the Specifications of Unlabeled D/C Generators?

[BonesSheppard]

Hi I am working on a wind turbine competition as far as the competition is going, designing my turbine and everything else, it's actually going quite well so far. But the one aspect which I have been scratching my head for a while has been the generators I have to use to make electrical energy. As part of the competition I was given 3 unlabeled D/C generators of which I must choose 1 ( I believe they're D/C generators although I am not sure) I figure I could determine its specifications if I run each generator at such and such an RPM for each generator then with a multi-meter measure the volts and amps. My questions would then be:

[1] Is this a good way to determine each generators specifications? [2] If I keep increasing the RPM to acquire accurate measurements is there a risk I can accidentally destroy my generators? [3] Is there a way I can figure out if it is A/C, D/C (good band by the way lol) [4] Is there a maximum electrical output that each generator is constrained by in which if it try to pass a certain RPM no further gains will be made?

Lastly I was given vague instructions, but the instructions said there are 3 generators however I was also given a 4th of some kind motor/generator, I am uncertain what it is, it has alligator clipping but no axle extrusion from which I could spin it to try and see its output. I would genuinely appreciate any help, there so small I was afraid to test any of them for fear I might break them and if I break them the organization said they will not give me replacement generators so I decided to come here for help :D. Thank you again for taking the time to read this I have pictures in the attachments below in case you were wondering what they looked like.

 

[Merlin3189]

They certainly look like small permanent magnet DC motors.
You should certainly be able to run them up to 6000 rpm safely and measure the DC voltage. Probably you could go to double that.
The open circuit voltage should be linearly proportional to speed.
You can measure their resistance and calculate the maximum current (short circuit current) for any speed.
What their maximum power handling capacity is (I²R), I don't know, but if they are the sort of size they look, I'd guess about 5W.