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Behold The Hyundai Uni Wheel. Transportation May Never Be The Same
(cleantechnica.com)
This is a most excellent place for technology news and articles.
If you're gonna go through all this trouble, why not put motors directly into the wheels? Then you can bypass the drivetrain all together and directly power the wheels.
4 motors is more expensive than 1 motor and a bunch of gears
Do really need need 4?
If you cant get by on 2, you might have less power, but you can get better efficiency. With better efficiency you can have a smaller battery for the same range and reduce some of your increased cost that way.