Originally posted by bsindel
Danny03, you are right in that generally speaking diodes do allow current flow in only one direction. However, one of the neat things that a typical silicon rectifier diode does is that when it is forward biased, conducting current, it develps a voltage drop across it of approximately 0.62 volts and this voltage will remain fairly constant over a wide range of current flow. This characteristic makes for a very simple, inexpensive, and reliable voltage regulator. At least to an old electronics hacker like me.
Bill
Yes, this is a common way of dropping a fixed amount of voltage, but just be sure not to get it confused (for any non-electronics enthusists) with genuine "regulation." A fully charged 6V pack running at, say, 6.75V, would drop to approx. 5.5V with two diodes in line. Then, at (near) end of capacity, battery voltage of 5.5V would be dropped to approx. 4.25V. Within specs for operation, but servos would be just a little slower.
FWIW suggestion, also: If needing to drop voltage for just one servo, consider placing diode(s) in supply line to that servo only. Thay way, there is no additional risk to Rx and other servos if diodes should fail. Also, other servos still get benefit of higher voltage if that is desired for speed/torque.
Finally, be sure to use diode(s) with high enough current rating!