Page 23 - CNC Robotics

Chapter 2 / Electronics

All the motors draw 1.4 amps per channel, but the step-syn
motors are rated at 4.5 volts and the Pacific Scientific motor can be
given a maximum of 170 volts. Alt hough I'm not using Pacific
Scientific motors in this project, if yo u are unable to find suitable
surplus steppers you may wish to purchase new ones. WARNING:
The stepper motor driver boards described in this chapter can drive
both of these motors, but you can only use up to 36 volts for motor
power-too many volts will fry the L298 integrated circuit. A com -
pany called ST Microelectronics has graciously given me permis-
sion to reproduce the data sheets and app lication notes in their
entirety in this chapter (see pages 22 through 75). These docu-
ments are the basis of th e driver board design. Read them thor-
oughly to gain a greater understanding of the strengths and limi-
tations of the L297/L298 integrated circuits (referred to as ICs) in
this app lication.

Stepper Motor Driver Circuit

The stepper motordriver boards are th e muscles of the CNC machine.
They receive signals from the computer that indicate whic h direc-
ti on that axis w ill travel and how far it wi ll move. They are the
muscles because as they receive direction and step signals from
Figure 2.4
L297 stepper motor
controller IC.

Figure 2.5
L298 H Bridge IC.

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