From the number of poles, a stepper motor should be a useful demonstration generator for an odd LED or three, when run by a slow running steam or hit and miss IC engine. PM Hand tool (drill) motors usually run at 10s. of thousands rpm to develop their power: I.E. Relatively small voltages from the DC battery but relatively high current: a 240W motor at 24V is drawing 10A on load. If run as a generator at less than 1000rpm you may only get 1 or 2 volts, - and similarly only tens of milliamps as a result. - The net power output being only a couple of watts. Gearing to get the generator speed you want can sap all the engine's power.
Conversely, a stepper motor, with 10 or more times the poles of a "power" motor, will generate the voltages at low revs but with very small current (amps) - as demonstrated by Ray - thus generating a few watts but at (possibly?) more useable voltages? I suspect these devices vary so much for different applications, makes, and sizes there is no simple rule to getting a stepper motor to match your application except by trial and tribulation!
I would be keen to use a diode bridge to convert the stepper motor output to DC to eliminate the high frequency from ruining any downstream (semi-conductor) devices, other than resistance wire bulbs.
Personally, I look to bicycle generators for my small steam engines, as they are designed to generate the single figure voltages and currents for torch bulbs at speeds suitable for the low speeds and low power of my engines, with small enough belt drives to look OK. They can be hidden inside "generator shaped" housings as well!
For some I use bridge diodes to rectify the variable frequency AC, then a Buck controller to get the controlled DC output for the LEDs that I have. This configuration may suit Ray - with parts such as these but that you select to match your input voltage and output voltages?
W04M 400V Bridge Rectifier Diode 1.5A
6-24V Input to 5V 2A Output USB Charger Module DC-DC Buck Step-Down Converter
Thanks to all contributors here as I have learned a lot about stepper motors, from a zero baseline of knowledge!