PCB motor

[RikStarmans]

Hey @atomic14,

In the past, I made a small script to create pcb motors, see https://github.com/hstarmans/pcb-motor, in combination with some experimental notes and basic equations which govern the system.
I am using this to rotate a mirror or prism in a laser scanner (see https://hackaday.io/project/21933-prism-laser-scanner). I also did quite some experiments on Hall sensors, different magnet configurations of which you can find videos online.
My main question; do you have any idea why people use trapezoidal tracks? Is the track length longer than the Archimedean spiral?

Anyhow, thanks for the video!

[cgreening]

Very cool - I wish I'd seen your work before starting mine - there's useful stuff there.

To answer your question, we're not sure at the moment - but it does seem to be a popular choice. Our working theory at the moment is that with a circular coil you have to have the magnet aligned perfectly with the centre of the coil, but with the long trapezoid tracks you have a much wider magnetic field for the magnet to move across - but we're not sure to be honest.

[RikStarmans]

Okay will write that down..

Some things I would recommend;

• use a thin PCB (I now use 0.8 mm) and a 4 layer board
• a thin PCB is most crucial as EM force drops with the square
• I couldn't spin up the rotor without hall sensors. I am not using a micro-controller but an FGPA programmed in python
  This makes it harder to write a good algo.
• There are articles online which further enhance the fields with ferrites
  Carl uses a metal encasing and 10 magnets see https://youtu.be/zeGKYIcLMIs?t=1186

[cooked]

Hey,
good to see a lot of traction on the topic.
I'm also working (very early steps) on a parametric PCB stator plugin (some notes-to-self and GitHub repo ), a nice learning curve for all things Kicad plugins.
give a shout if you're interested to join efforts at any point in time

[cgreening]

I think the GitHub repo link isn't working.

One thing that were really trying to get a grip on is the shape of the coils.

From reading a few papers it does seem that the radial lines seem to be the parts that do the work and the top and bottom of the coils don't contribute anything.

[hstarmans]

I did think of it and believe the explanation to be quite simple;
Lorentz law gives us the force created by a current carrying loop. A circular loop does have largest track length per surface area but not in the best direction.
A trapezoid has two equal sides which are optimal. The top and bottom of the trapezoid have zero contribution.
This argument does not hold if you want to flap something. Here you would use the Archimedean spiral to simply pull an object inward or outward.
I can imagine you could use calculus to find the optimal shape, or do numerical computation to proof this.
There is also some information here on the magnets that could be interesting https://things-in-motion.blogspot.com/2019/01/selecting-best-pole-and-slot.html

[cooked]

@cgreening oops, sorry about that. forgot to change visibility but should be good now

[RikStarmans]

@cgreening thank you for your answer in video https://www.youtube.com/watch?v=wvWB8099BkU
Good explanation!! Impressed, Can you share the script for the simulator? There are some follow up questions:
- how can the motor best be shielded, is it required to be shielded due to safety requirements or can this be sold as is?
- there are articles online where people add ferrites and further enhance the field (lost the article)
- you can use ferrites to pin the rotor

[cgreening]

Added the script - I've messed something up somewhere in the magnet-coil interaction simulation - need to try and work out what I've done...

In terms of shielding, it's probably no worse than any other BLDC motor in terms of noise/emissions though most motors do have a metal shell. Probably won't sell it as a finished product. There would be a lot of work to get it certified and it's pretty easy for people to get their own manufactured.

[cooked]

@cgreening thanks for the great work! I'm wondering if you have any test / validation planned... torque output would be of primary interest I believe

PS: I'm waiting for my stators to come in this week (made by Jlcpcb) and keeping an eye on their coupons for the manufacture of 6-layers ones (coming on 24th)