Hello,
I have a motor that works off a 1.5 volt battery and i would like yo slow it down to about half its speed with the fully charged battery. I think i have to put a resistor in parrallel with it or should i be using some other part and what value would it need to be. Thanks

 

A resistor in parallel will only discharge the battery faster.
To do it with a resistor put the resistor in series. This will reduce the speed but will also reduce the motor power.

 

Hello,
ok if i understand it i put a resistor on the positive side of the motor. The only drawback with this as far as im aware is that when the motor as been running for a bit it will slow domn and stop, and there will still be juice left in the battery. Is there a method i can use up all the battery power. I know i could do it with a variable resistor but is there another way.

 

Using a constant current source, but it's not much use on a 1.5v battery, your better using different power source.

 

use a diode

 

Hello,
ok if i understand it i put a resistor on the positive side of the motor. The only drawback with this as far as im aware is that when the motor as been running for a bit it will slow domn and stop, and there will still be juice left in the battery. Is there a method i can use up all the battery power. I know i could do it with a variable resistor but is there another way.

Put a switch across the resistor to connect the motor directly to the battery as the battery runs down.

 

What is the motor used for and what is the rated voltage that is expected? @ 0.75 volts, it may not run and if it does, it's power will be reduced. Have you already tried the resistor idea?

I'd recommend a PWM method. You can search online for a simple circuit like this*, but basically, the circuit would "chop" the 1.5V so that it is on (almost) only half the time. I saw "almost" because a simple circuit uses a 555 IC, which can't be on exactly half the time. But you can get close. I've used a 555 circuit that was on 52% of the time.

Of course, this will draw some extra current and may not be practical for you.

* the link to a circuit is presented as an example, not a solution to your case. For example, the switch (on the right) is not necessary unless you plan on reversing the motor.