In article , harry wrote:

Tell us all how you can make a motor run on DC.

http://en.wikipedia.org/wiki/Homopolar_motor
Runs on DC. No commutator, no inverter. Not a lot of practical use,
but it works.

http://en.wikipedia.org/wiki/Railgun
Has practical use, and is at least arguably a kind of linear motor.
No commutator, no inverter. You put a DC pulse in, and get movement out....