D1 and D2 can be inserted to lower the power supply output voltage. You can series several diodes in that arragement, each diode will lower the output approximately .7VDC. R1 is not critcal in value. It is a bleed resistor to remove the charge of C1 after power is shutoff. For 32VDC, 470 ohms at 2 watts is a reasonable value. Fusing the output individually to each motor driver is a good practice. Size the fuse to the motor current. D3 provides a path for motor emf when and if the fuse blows on bipolar drivers, otherwise your motor driver could suffer potential failure.
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