I am looking for two items: A 1.5 to 3.0-V dc motor (a very small motor) with a rheostatic speed control, and a spring-resisting pushbutton that allows increased current to flow to the motor (to vary its speed) depending on how hard the button is pushed. The motor will drive a small-diameter wheel (approximately 1.4 in. in diameter) that feeds a wire at from 1 to 3 ft/min. The accelerated mass is from 0.5 to 1 oz. The button and attached variable resistance must also be small. @ Ask The Experts

Motors and Motion Control Q&A

I am looking for two items: A 1.5 to 3.0-V dc motor (a very small motor) with a rheostatic speed control, and a spring-resisting pushbutton that allows increased current to flow to the motor (to vary its speed) depending on how hard the button is pushed. The motor will drive a small-diameter wheel (approximately 1.4 in. in diameter) that feeds a wire at from 1 to 3 ft/min. The accelerated mass is from 0.5 to 1 oz. The button and attached variable resistance must also be small.

Answered April 29th, 2010 by Expert: Paul McGrath

I first want to point out the difference between a rheostat and a potentiometer. A rheostat is a simple, two-terminal variable resistor, while a potentiometer is a three-terminal variable resistor. There are two main terminals that, if measured, represent the maximum value of the resistor. The third (center) terminal is called the wiper. The wiper, when in the center position, splits the difference of the resistor with respect to each of the main terminals.

Potentiometers are used as voltage dividers and are much more common than rheostats. They can also be used as rheostats, but in such cases, one main terminal and the wiper terminal would be used.

We don’t sell rheostats or potentiometers, but many of our controllers have built-in potentiometers. We do have motors that can operate on very low voltages, and you can certainly vary the speed by adjusting the voltage. With brushed motors, it is completely linear.

Paul McGrath

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