First of all you need to know at what voltage is the motor rated. Whatever the case, you *could* wire a 10 Ohm resistor in series with the motor, which should drop the motor voltage to 4V. If the motor doesn't go at full speed even at 6V, then lower the resistor. For 3V, try 20 Ohm. A zener diode could do too!

Hope this helps.

Put a 3 Volt flashlight bulb in series with your motor



which has the same current rating as your motor:



(Example: 100ma, 500mA, 1 Ampere).



The bulb shouldn't draw to much power from the motor while



Solar output Voltage is low.

Find R = ( 6v - 3v ) / motor current at full load





Wattage of R = ( motor full load current ) ^2 * R





Buy resistor wattage ( choose the size of resistor ) in market by double the wattage rate from above calculation.

I would recommend some kind of simple voltage regulator.

Question: I have a small motor that runs off my solar panel, the solar panel fluctuates from 1V to 6 V. I am worried that I might burn up this small motor. I want to limit the amount of V going into the motor to 3 volts. Do I need a resistor? is so what kind?