First post here, it's probably a very easy fix for most of you here. Right now I'm trying to use a digital potentiometer in a voltage divider to step down a voltage from 5v to a range of 3 - 1.5 volts that will go into a set of 4 DC vibrational motors. The resistance of the digipot is in the range 10Kohm - 1Kohm while the motors are only about 15ohms.
In order to supply enough current I put a voltage buffer in front of the motor however that still doesn't fix my problem. I'm able to control the output voltage of the buffer well without the motor attached in the 3 - 1.5 volt range however as soon as I plug in the motor the voltage drops to 0.420 V (according to an oscilloscope).
I'm using a UA741 for my op amp and TIP120 as well in the circuit. Power is being supplied from a simple DC power supply, I plan to eventually use a battery to supply power. I've attached a drawing of the schematic and links to the data sheets below.
TIP120 NPN Transistor:http://www.bc-robotics.com/datasheets/Tip-120.pdf
UA741 OP amp: http://www.ti.com/lit/ds/symlink/ua741.pdf