Geared DC Motor with Magnetic Encoder Outputs - 7 VDC 1:20 Ratio

The first step in a robotics project is to get a motor spinning. Once you've done that, you quickly learn that not all motors go the same speed, even if they are the same part number! There are always variations that relate to voltage, environment, and manufacturing changes. So, the second step is to figure out how fast it's going! Turns out that's not so easy, but the best way to get started is to add an encoder wheel and an optical or magnetic counter. As the motor turns, the attached encoder wheel spins, causing the counter to detect each passing spoke, and that lets your microcontroller count and determine speed.