I am looking at using this motor (Catalog #: 273-223) found at pretty much every Radio Shack. I will be providing it and one other identical motor with 1.5 volts and would like to be able to control the speed of the one but not the other. Looking through the bins at Radio Shack I realized that with my 0 knowledge of electronics that I couldn’t possibly know which one to purchase. You’re mission, if you choose to accept it, is to find the best potentiometer for this application available in store. Thanks in advance to anyone that can help me out!
Look for a rheostat
Your best bet is to use any of the linear taper carbon-film pots (1/4 watt) and use them to adjust a variable-voltage regulator LM317, then use the output from that to control the speed. DC motor speed is controlled by voltage, so that half the voltage will run at half the speed. You’ll want your voltage to adjust from 0 to 1.5 V.
NB - this is an inefficient, if simple, method of speed control. More efficient speed controllers switch the power either on at full full voltage, or off. Adjusting the duty cycle affects the average voltage, e.g., a 50% duty cycle would reduce the effective voltage and therefore the speed, by 50%, as well.