VFD's / Skates

Hello,

My server decided to kick me off for a while so I'm currently trying to
sort that out along with a thousand other problems to do with these
computers (And to think I used to enjoy using them!). I had a look at some
VFD's, could someone explain to me how they actually work? I've never seen
these before. They tell me the voltage and phases they're capable of but is
that the power going in or the power going out? I am looking for one roughly
twice the power I need yes? I am having a time shifting the junk out the
garage to see how much space I can make, my hands are black with soot from
the welding torch. One last thing, has anyone seen a web page or information
about making machinery skates? I know I should be using roller about 20mm -
25mm in diameter but I'd like to see how I should join them to a base and
other things like how thick the base should be to stop it bending.

Thanks in advance,

John He.