Low voltage motor with arduino
Many motor drivers can directly drive a 1.5 volt motor from a 5 V (or more) power supply,
because they have built-in current limiters ("chopper circuit").

Alas, the Lady Ada motor shield FAQ specifically says:
"Can this shield control small 3V motors? Not really, its meant for larger, 6V+ motors."

It appears to me that you can add a few power resistors to (inefficiently) drive a 1.5 V motor from the adafruit motor shield using the "L/R driver" system.

The "Current Control of Stepper Motors" document describes the older, less efficient "L/R driver" system, and compares it to the more modern and efficient (but complicated) "chopper circuit".

This motor shield uses the L293D motor driver chip, which simply drives the output high or low, without any limit except its thermal protection limit.
To convert it to a L/R driver system:


Ir: Find the rated current Ir (if it's not written on the motor and you can't find the datasheet, measure the motionless coil resistance Rcoil with a multimeter and calculate Ir = 1.5 V / Rcoil). If this is more than the 0.6 A that the L293D can provide, do the remaining calculations with Ir = 0.6 A instead. (Example: measure 3 Ohms; Ir = 1.5 V / 3 Ohms so Ir = 0.5 A).
Vdd: What is the voltage Vdd of your power supply? (Example: VDD = 5V, but lots of people prefer 12 V.)
P: Your power resistors need to dissipate up to P = Ir*(Vdd - 1.5 V)/2. (Example: P = 0.5 A * (5 V - 1.5 V)/2 = 0.88 W)
R: Your power resistors need a resistance of R = (Vdd - 1.5 V)/(2*Ir). (Example: R = (5 V - 1.5 V)/(2* 0.5 A) gives R = 3.5 Ohms).
Get or make 4 identical power resistors that have approximately the above resistance and at least the above power rating. (Example: a 5 W, 4.7 Ohm resistor will work nicely ... or a series of 4 quarter-watt resistors in series, each one 1 Ohm, produces a 1 W, 4 Ohm resistor, which will also work nicely.)
Connect one end of each resistor to one of the 4 halfbridge terminals on one side of the motor shield, the other end to one of the 4 pins of your bipolar stepper motor.


I assumed your motor was a 4 wire (bipolar) stepper motor.
Does this L/R thing work for DC motors also?

The L293D datasheet says it requires something in the range of 4.5 V to 36 V to function properly, so I wouldn't bother trying to power the adafruit motor shield from anything less than 4.5 V.