Summary

This is a converter wheelbase that makes you makes you build Lego trains and drive them on your Brio/Ikea tracks.

It consist of a base, wheels and a center that can tilt in the base, so the train can drive over bridges. On the center I have glued on a lego turntable.
You can get the turntables directly from lego https://shop.lego.com/da-DK/Pick-a-Brick search for "turn plate"
or you can use a site like BrickOwl https://www.brickowl.com/catalog/lego-turntable-2-x-2-with-medium-stone-gray-top-74340

Finding the right magnet can be a hassle. I used a Ø13x3,9xØ3,5mm ferrite ring magnet, that works really well.
https://larko.dk/ferrit-ring-magnet (Danish site)
If you find any other magnets that works, please put it in the comments.

I mounted the magnet with a 11mm round headed nail, so the trains can turn without disconnecting each other.
https://www.stofogstil.dk/polstersoem-11mm-oxid-30stk-49060/ (Danish site)

I cut the head of a 1,4mm nail to mount the center and some 2mm nails to mount the wheels. These I had laying around, so no links for those.