There are a few ways of doing it. The easiest thing to do (and thats a relative term) is to have a "knife" that goes into the
deck that is connected to the piece. Usually you do two knifes on one piece. Connected in to the knife is a cable. The cable runs under the
deck through a series of pulleys that then connect to a
winch. When the cable is pulled, the piece moves.
Now... in order to get this all to work, you have to have a
winch and a raised
deck to run the cables through.
The other way to do it is to put the drive on the piece itself. Some then still have a knife that goes into the
deck to keep the piece going straight. This is method is found on most touring shows because it makes
load in happen faster. However, it costs a lot more to do and requires cables to follow the piece, unless it is battery powered.
All in all, this is not a cheap thing to do. Building a false
deck across and entire
stage can cost 6k or more. Adding to that, a
winch system can cost 5-10k to
build.
Creative Connors and Hudson scenic both offer
winch systems for rental, if you want to take a look at what they have.
Creative Conners, Inc.