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.
If you want to do one better, add a second counter, and now you can tell direction as well as speed! All this wiring is kind of a pain, so that’s why this motor is really nice! It has a magnetic wheel and two hall effect sensors already attached. Using this motor is a breeze, and it’s a nice small motor as well, in the ‘standard’ N20 size.
Provide 4.5 to 6V DC (nominal) to the white and red wires — these connect to your motor driver, and can be PWM’d for speed adjustment and direction by using an H-bridge.
Connect the black wire to your microcontroller ground pin, and the blue wire to 3-5V DC (we tried both, works fine) use whichever voltage your microcontroller uses. Then you can read the hall effect outputs on the yellow and green wires. We have an example sketch here for Arduino, it can be adapted to other languages — basically you just want to interrupt on one of the encoder pins, use count the time since the last interrupt, and multiply the count time by 14-counts-per-revolution and the gear ratio.
This particular DC motor comes with 1:298 gear ratio, uses 6V nominal power for the motor and draws about 100 mA (200 mA when stalled). The gear ratio will not affect the current draw but does change the torque and RPM. See below for the no load/rated/stall current, RPM and torque for a range of ratios!
- Dimensions (excluding shaft): 30.5mm x 18.5mm
- Wire Length: ~150mm long
Ratio Comparison Table: