The ends of the field and armature magnets should be separated an eighth of an inch. The hub for the commutators is three-quarters of an inch long and three-quarters of an inch in diameter. The commutators are made as described for the uni-direction current machine, care being taken to keep the holding screws from touching the shaft. A three-quarter-inch cube of wood is mounted on the base, under the commutator hub, and to this the brushes and binding-posts are made fast, as shown in Fig. 39. Unless the armature happens to be in a certain position this motor is not self-starting, but a twist on the pulley, as the current is turned on, will give it the necessary start. Its speed will then depend on the amount of current forced through the coils. Another Simple Motor Another type of motor is shown in Fig. 44, where one field-winding magnetizes both the core and the lugs. The frame of this motor is made up of two plates of soft iron a quarter of an inch thick, six inches long, and two inches and a half wide. Each plate is bent at one end so as to form a foot three-quarters of an inch long, and a half-inch hole is drilled one inch and a quarter up from the bottom, at the middle of each plate. Through this hole pass the machine-screws which hold the iron core in place between the side-plates. The core is made of three-quarter-inch round iron two inches and three-quarters long, and drilled and threaded at each end to receive the binding machine-screws. Two lugs are cut from iron, and hollowed at one side so that an armature two inches in diameter will rotate within them when made fast to the side-plates. The lugs are two inches and a half long, an inch wide, and two inches and a half high. From iron five-eighths of an inch wide and one-eighth of an inch thick make two side-strips with [L] ends. These are four inches long, and are provided with two holes so that the machine-screws which hold the lugs to the inside plates will also hold these strips in place, at the outside, as shown in Fig. 45. At the rear these strips extend half an inch beyond the frame. Across the back a brass strip of the same size as the iron strips is arranged. It is held at the ends by screws, or small bolts, made fast to the [L] ends of the side-strips. Directly in the middle of the back-strip a hole is made for the armature shaft, and beyond it the pulley is keyed or screwed fast to the shaft.