Hardware Reference
In-Depth Information
Figure 7-5.
Wave drive, two phase on
While this mode lacks the precision of half-step mode (next), it does enjoy the extra
torque advantage over all three modes.
Half-Step Mode
In half-step mode, a combination of the two prior modes is used. First, only one winding
is energized to point the rotor at the winding's pole (like one-phase mode). Then the next
pole is energized while keeping the prior winding energized. In this way, the rotor moves
a half step between the two poles, as with two-phase mode. Finally, the previous winding
is turned off, producing another half step. The precision is increased to a total of eight
steps in this manner.
This is clearly the most precise of the three modes. While it lacks some of the torque
of two-phase mode, it has on average more torque than one-phase mode.
In all of these modes, it is necessary to first pass current through the windings in one
direction, and then later in the reverse direction. This allows the bipolar stepper motor to
be built with less wire than the unipolar motor. In the unipolar design, only one or two of
the four center-tapped windings are used at one time. Consequently, the bipolar motor is
cheaper to manufacture and lighter in weight.
Figure
7-6
illustrates my test setup. At the left is a power supply that I rescued from
a discarded piece of equipment. To the right of the Raspberry Pi station, I have the L298
PCB wired up to the power and the Pi's GPIO pins. The remaining four wires go from the
drive PCB to the bipolar stepper motor (I left some sort of shaft attachment to the motor,
to make the rotation more visible).
