3-Phase Pulse Motor (Arduino Controlled)

thingiverse

This is a good project for someone wanting to build an Arduino controlled 3-phase pulse motor and needing a starting point that requires the least amount of engineering knowledge to initially build. This is my second pulse motor and it incorporates a few concepts I wanted to explore. The picture shows a single pole wired up and it will run with only the one pole just at reduced speed. One nice aspect of this design is that it doesn't require complicated coil winding - off the shelf 9x12mm 10mH inductors are used as shown in the photos. Each of these were measured at 14-15 ohms each and each pole consists of one hall sensor and 3 inductors wired in series. Each phase is offset 120 degrees and the coils should be driven from a 24V supply (12V won't be enough). Typical current draw was < 250mA but I tried so many different inductors that I lost track of the details. Magnets on the rotor are 1/2" (~12.8mm) x 1/4" (~6.4mm) N48 and are held in place by Gorilla-brand superglue. I recommend the bottle with the brush applicator as it is easy to apply. Apply glue liberally including over the outer face of the magnet to create a seal to help prevent the magnets from flying off. Perfect placement isn't very critical. You could probably use 6-7x 12mm x 1mm N35 magnets with no issues. The rotor spins freely on an ABEC-9 rated 608 bearing. The Hall switches are wired to signal the Arduino. The Arduino then turns on the mosfet isolated from the Arduino via an optocoupler. I made 3 JST female to female connector wires and stuck the hall switch in one end of the 3 pin wire. I then bent the hall sensor pins to fit the plastic mounting pieces as shown in the photo. The circuitry is as simple as you'd expect. Very basic circuits that you can find posted everywhere. One note: Make sure your Arduino code incorporates a safety mechanism to shut off power after a short pulse. If you make the logic such that the hall being triggered = power being on as it might be if you wired it directly without an MCU then non-movement of the rotor would cause power to run continuously through the triggered pole and it will catch fire and melt if left in this state for too long. Being able to control timing and integrate safety features is part of the fun I had with this project. It may be possible to integrate an "auto" start routine but I didn't bother and spun it manually to get it going. My parts list is: 2 Batteries - 12V sealed lead acid connected in series for a total of around 25V when fully charged. 9 Inductors - 9x12mm 10mH (25mH work too but I think the 10mH worked better) 1 608 skateboard bearing 4 Magnets - 1/2in x 1/4in cylindrical neodymium 3 Hall Switch ICs - I used OH 137 6 Mini micro JST 3pin - 3 PH and 3 XH preferably (see notes below) 1 MCU - Arduino or other 3 Mosfets - I used FQP30N06L 3 PC817 - I used optocouplers to isolate the mosfets from the Arduino. Common connectors, resistors, capacitors, wires, heat shrink, tape, bread boards, super glue, etc to make the circuitry and mount everything in place. Build notes: The 4 rotor magnets are oriented so that south poles face outward. It is important to know which face will trigger your hall switch. In my case the OH 137 must be oriented with the marked side toward the south pole otherwise it won't work. The inductors are wired to repel south pole, to figure this out, you'll need to test each inductor one at a time and see when power is applied whether the south pole is attracted or repelled. TinkerCad links in case you want to tweak the design: Rotor - https://tinkercad.com/things/lES9LRQXVPK Stator - https://tinkercad.com/things/2yzUta3qp1s Hall Bracket - https://tinkercad.com/things/2d8KDFGzbsm Bedini SSG-style triggering circuits are possible, instead of a hall switch you'd use another 9x12mm inductor. I tested this with a 200mH inductor that measured about 330 ohms as the "trigger coil." Worked fine. In all cases correct inductor orientation is important and failure to determine the correct orientation can cause poor operation. I used two Mini Micro JST PH 3 pin connector wires joined to form a complete female to female JST cable. Hall sensor went it one end and I soldered a male jst connector to my breadboard. At the time I was pretty ignorant on JST connectors so I'll share what I know now. JST connectors come in different sizes ( see: https://en.wikipedia.org/wiki/JST_connector ). JST connectors larger/smaller than PH may not fit nicely in the hall bracket, but the PH do not like to fit on a standard 2.54mm pitch breadboard. So I recommend using one PH and one XH 3pin soldered together to form a single wire for the hall sensors. This will make your life easier.