Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
Here's a quick little explanation of motor speed control. Motor equilibrium speed is based on voltage applied. PWM is used to set the voltage. For example, say you had a small DC motor and if you apply 12V it will spin at 1000 rpm. If you applied 6V it will then spin at about 500 rpm. If you have a 12V power supply (say a car battery) you can use PWM to create an average of 6V, or any other voltage across the motor and make it spin slower.
To create 6V, you would use a 50% duty cycle. To do this you could use a replay to switch power on and off to the motor. Usually this type of PWM is done using a frequency of 20 kHz or higher to keep the noise created above the human audible frequencies.