I had the pleasure of testing out a new brushless motor from Hitec called the Energy Propel 4108/40 Integrated Power Systems (Hitech part# 61097). This motor has a compact form factor and nice power to weight ratio. But the best part is that it has the ESC (electronic speed control) built into the motor housing - so controlling it is just a matter of sending a PWM (pulse width modulation) signal.

If I was using an RC transmitter/receiver it would be plug-n-play but since I was making a weed whacker I wanted a trigger system. I laser cut a trigger, mounted it to my Actobotics potentiometer and attached an extension spring I had laying around my shop.

Next I needed a way to read the analog voltage from the potentiometer and translate that into the PWM signal that the motor was expecting. I also wanted to drive a strip of neopixels (RGB LEDs).

I used an Arduino Nano V3 to do the processing. I also needed a BEC (battery eliminating circuit) aka voltage regulator to step down the battery voltage to something that the Arduino would be happy with. The Arduino Nano’s recommended input voltage is 7-12 V, so I used a 9V step-up/down voltage regulator. I 3d printed a mount to hold both boards that would slide into the carbon fiber body of the weed whacker.

After I got my potentiometer installed I needed to read the value I was getting for a full trigger pull and set the potMin and potMax variables in the sketch. The pot I used was a 270° turn pot but in the physical configuration I set up it only rotates about 30°. Fortunately this did not seem to noticeably affect the quality of the proportional speed control.