Not sure how big the model is but have you ever seen the Lego MicroMotor?
It's tiny, torquey, geared right down so ideal for radars and fits inside a 2x2 Lego brick housing.
DC max 9V but runs on very low voltages at slower speeds
Quite rare but very useful. (It's used in the old Lego Technic Space Shuttle to open the satellite's solar panels).