In google search to answer that question, the most discussion about DC motors was on this site. Here is the DC motor question - I sell to the healthcare market, have got a new line from a manufacturer which is powered by 4 DC motors - basically a bed that contorts into many different positions.
The "cheap" brands use 3 or 4 AC motors - the better use DC motors. There must be a reason why the higher priced units use DC. The manufacturer did not answer that question - they presume sales types don't care about such things - but somebody will ask and DUH is not the answer I want to give.
THanks - and I am not a troll -will be out next week selling these things.