AC induction motors are everywhere, from ceiling fans to vehicles. They’re reliable, simple, and rugged — but there are some disadvantages. It’s difficult to control the speed without complex electronics, and precisely placing the shaft at a given angle is next to impossible. But the core of these common induction machines can be modified and rewired into brushless DC (BLDC) motors, provided you have a few tools on hand as [Austin] demonstrates.

To convert an AC induction motor to a brushless DC electric motor (BLDC), the stator needs to be completely rewired. It also needs a number of poles proportional to the number of phases of the BLDC controller, and in this case the 24-pole motor could accommodate the three phases. [Austin] removed the original stator windings and hand-wound his own in a 16-pole configuration. The rotor needs modification as well, so he turned the rotor on a lathe and then added a set of permanent magnets secured to the rotor with JB Weld. From there it just needs some hall effect sensors, a motor controller and power to get spinning.

At this point the motor could be used for anything a BLDC motor would be used. For this project, [Austin] is putting it on a bicycle. A 3D printed pulley mounts to the fixed gear on the rear wheel, and a motor controller, battery, and some tensioners are all that is left to get this bike under power. His tests show it comfortably drawing around 1.3 kW so you may want to limit this if you’re in Europe but other than that it works extremely well and reminds us of one of our favorite ebike conversions based on a washing machine motor instead of a drill press.

A knob can make a surprisingly versatile interface, particularly if it’s the SmartKnob, which builds a knob around a BLDC motor for programmable haptic response. It can rotate freely or with a set resistance, spring back to a fixed point when released, stick at detent points, and completely change its behavior as the interface demands. For people inexperienced in electronic assembly, though, smartknobs can be difficult to assemble. That’s why [Kokensha Tech] designed a simpler version, while at the same time letting it use a wider range of BLDC motors.

In addition to a motor, the original design used a magnetic encoder to detect position and a strain gauge to detect pressure on the knob. A circular LCD on the knob itself provided visual feedback, but it also required the motor to have a hollow center shaft. The LCD control wires running through the shaft proved tricky to assemble.  [Kokensha Tech] moved the display out of the knob and onto a separate breakout board, which plugs into the controller board. This greatly broadens the range of compatible motors, since they no longer need a hollow shaft.

The motor now fits on a separate carrier board, which makes it easier to swap out different motors. The carrier board has mounting holes sized for a wide variety of motors, and four different types of motor connectors. [Kokensha Tech] also redesigned the rest of the PCB for easier soldering, while avoiding components with narrow pin spacing whenever possible. The original design used a LILYGO T-micro32 Plus MCU. The ESP32 is both cheaper and easier to solder, so it was a no-brainer to swap it in. 

We’ve covered the original SmartKnob before, including a more in-depth look at its design. We’ve also seen another project use BLDCs and field-oriented control to make haptic knobs.