Hi Jumbolino,
Do you mean a light dimmer switch?
They are for AC, you might be able to
run one through a bridge rectifier
to the motor, assuming its run from
the AC mains.
The packaging will usually say its not
meant for inductive loads, so you may
find it wont cope.
Make sure that the unit is properly
earthed, don't rely on "double
insulation".
An AC electric shock can hurt, but a
DC electric shock can 'grab' and make
it difficult to let go, so take care.
Regards, John