Are these what I think they are?

and can we make mini rotary convertors or still buy them?

These giant rotary converters are in fact DC generators, or Dynamos if you will.
http://en.wikipedia.org/wiki/Rotary_converter
They operate on the principle by using commutators and brushes in order to electro-mechanically rectify the alternating current that's being generated in a rotor as it spins in a (electro)magnetic field.
http://www.animations.physics.unsw.edu.au/jw/electricmotors.html
A very common type of Dynamo is actually the motor used in toy cars as it also can be used as a DC generator.
Hope this helps.

what happens when we pulse a turning dynamo?  in this design style in video