The brushes are made from thin gauge sheet-copper according to the shape and dimensions shown in Figure 261.
They are bent at right angles and mounted on the base on either side of the commutator with small round-headed wood screws.
The completed dynamo is shown in Figure 262. One end of the shaft is provided with a small pulley to accommodate a small leather belt.
Fig. 261.—The Brushes.
The dynamo is connected as a "shunt" machine, that is, one terminal of the field magnet is connected to one of the brushes, and the other terminal to the other brush.
A wire is then led from each of the brushes to a binding-post.
A shunt dynamo will only generate when run in a certain direction. In order to make it generate when run in the opposite direction, it is necessary to reverse the field connections.
The dynamo just described should have an output of from 10 to 15 watts and deliver about 6 volts and 1 3/4 to 2 1/2 amperes.
In order to secure current from the dynamo it will first be necessary to magnetize the field by connecting it to several batteries.