Theres Plenty of ways to do the 4 bar lifter systems.
Theres the ones powered by actuators like on Biohazard or theres a few other easier and harder ways of doing it.
Theres a few robots that have a motor or motors attatched to the rear arm on the 4 bar setup (where your would normally pivot the rear bar at the bottom) and as they turn the rear arm moves. hard to explain try look at these see if you can work out what im talking about.
http://s189.photobucket.com/albums/z244/TXROBOTICS/Combat%20Robotics/4-Bar%20Robots/?action=view&current=lifterwork.jpghttp://s189.photobucket.com/albums/z...cs/4-Bar%20Rob ots/?action=view&current=lifterwork.jpg

http://s189.photobucket.com/albums/z244/TXROBOTICS/Combat%20Robotics/4-Bar%20Robots/?action=view&current=Jan11_02.jpghttp://s189.photobucket.com/albums/z...cs/4-Bar%20Rob ots/?action=view&current=Jan11_02.jpg

http://s189.photobucket.com/albums/z244/TXROBOTICS/Combat%20Robotics/4-Bar%20Robots/?action=view&current=ioguts.jpghttp://s189.photobucket.com/albums/z...cs/4-Bar%20Rob ots/?action=view&current=ioguts.jpg

http://s189.photobucket.com/albums/z244/TXROBOTICS/Combat%20Robotics/4-Bar%20Robots/?action=view&current=tb4_66.jpghttp://s189.photobucket.com/albums/z...cs/4-Bar%20Rob ots/?action=view&current=tb4_66.jpg

ok?
Or you could use like a screw style lifter. i think elvis uses this kind of method altho its not a 4 bar system.
http://s189.photobucket.com/albums/z244/TXROBOTICS/Combat%20Robotics/4-Bar%20Robots/?action=view&current=IMG_2729.jpghttp://s189.photobucket.com/albums/z...cs/4-Bar%20Rob ots/?action=view&current=IMG_2729.jpg

Elvis:
http://s189.photobucket.com/albums/z244/TXROBOTICS/Combat%20Robotics/Others%20Robots/?action=view&current=elvis.jpghttp://s189.photobucket.com/albums/z...cs/Others%20Ro bots/?action=view&current=elvis.jpg

Or theres another kind of complex method like used in storm 2.
http://www.teamstorm.com/storm2/storm2b.htmhttp://www.teamstorm.com/storm2/storm2b.htm

Well this might not have been any help but i tryed.
Heres a link to a few pics i have collected of 4 bar lifter robots. theres a few other design types in there.
http://s189.photobucket.com/albums/z244/TXROBOTICS/Combat%20Robotics/4-Bar%20Robots/http://s189.photobucket.com/albums/z...cs/4-Bar%20Rob ots/

Edit: BTW im new to this hobby so double check with somebody a little more experienced if you decide to use any of the methods above. The guys on here are a huge help and you should definitely take note of everything these guys say it well help you out alot in the end.
Cheers.

(Message edited by xtreme on September 02, 200