I'm new to 3d printing personally, I only got a printer a few months ago! I was very kindly gifted an Anet A8 by someone from work when they upgraded to a Prusa unit. I have made quite a few modifications, both to improve print quality and to reduce the risk of fire (something that the A8 is notorious for). I was thrown in at the deep end a bit, since I had a lot of complex parts to print, but after the mods and slicer tweaking, I'm really happy with the prints I'm getting. I might build my own printer from scratch once I finish the ROV.
I originally designed the thruster to have 8 magnets in the prop and 8 in the rotor. This did work, but it couldn't couple enough torque to work reliably. I redesigned the rotor to hold triple-stacked magnet groups, with the prop still only holding 8 magnets because of a lack of space. This results in a total of 16 magnets. The magnets are not actually very strong, they are only 20 x 6 x 2mm, designed for holding cupboard doors closed. They are neodymium though, so quite strong for their size.
I found that the arrangement of the magnets is just as important as their strength. I arranged the magnets in a way that they all amplify each other's fields (due to the close proximity and alternating polarity in the rotor in particular), which makes an impressive difference in the torque which can be coupled through the pipe. Including the pipe wall and air gaps, there is an approximately 4mm distance between the inner and outer magnets.
Below is a rough sketch of what the magnet arrangement I used, as well as what the magnetic flux might look like (I'm no magnet physicist though, so take it with a pinch of salt). I might get some iron filings to check this, and satisfy my curiosity.
- Magnetic Flux Diagram compressed.jpeg (182.2 KiB) Viewed 5551 times