> suggestions for small motors

Cassette motor (3-12V, may be permanent magnet), VCR capstan motor,
DVD/CD/FDD motor, cellphone vibrator motor, slot car or RC motor

> not sure if a stepper motor would be more efficient

A stepper puts out pulses, which might be adequate V if the rotation
is fast enough. The detent or cogging causes a quick movement of the
rotor past the pole(s) so you may get more peak voltage out of a stepper
at a slower speed than a DC motor. Low average though. There might
be enough for a diode-capacitor doubler, but that may be too lossy at
low V input

> calculating the potential output voltage and current of a motor when
> used as a generator?

I would expect the output to be about the same as whatever voltage
it takes to run the motor at a particular speed, although motors aren't
linear devices. For example, too low a run voltage won't overcome
inertia etc and will get dissipated in the windings with no movement,
or the last few % of PWM doesn't make a significant difference

> done a project like this and has any advice

I've seen small motors used as anemometers in weather stations and
for windmill generators but they are properly rotating. The velocity and
drive energy of your pendulum is going to be a big factor. Small motors,
apart from steppers, tend to be high-revving

Have you considered a coil and magnet instead ? I've seen creations
using a relay coil (many turns of fine wire) and a neodymium magnet
passing it or flipping near it as a magneto/dynamo

Joe

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