How do you underspeed shunt motor?

To underspeed a shunt motor, you can reduce the armature voltage by using a variable resistor or rheostat in series with the armature circuit. This decreases the current flowing through the armature, thereby reducing the motor's speed. Additionally, you can also adjust the field current, as a decrease in field strength will increase the motor's speed, but this must be done carefully to prevent motor instability. Always ensure to monitor the motor to avoid overheating or damage.