Designing for DC voltage drop in low gauge wire
Generally, when you need to tightly regulate the voltage for a variable load at some distance from the power supply, you look for a power supply that has "remote sense" terminals. These allow you to create a 4-wire connection to the load, and this allows the internal regulator to compensate for the voltage drop in the main current-carrying wires.

However, you may be over-thinking the problem. AWG18 wire has a resistance of 20&nbsp;m&Omega;/m, so a 25-meter run of 2-conductor cable has a total resistance of about 1&nbsp;&Omega;. Even with a motor drawing 1&nbsp;A, this would only create a voltage drop of 1&nbsp;V.

If all of your motors have about the same length of cable running to them, it may be sufficient to simply turn the voltage of the power supply up by 1&nbsp;V to compensate for the cable drop. Most pre-built power supply modules have an adjustment control for just that purpose.