Over build ? No SUch Thing !!!! < spoken like a true Technical Director>
We just did it as well. I built the forestage area out of two very large "stress-skin" platforms. The upstage edges of these were re-inforced then hinged to the upstage platform by 8, 4.5 inch heavy-duty door hinges. < the commercial kind, for 600# doors>. About a foot and a half back from the downstageedge I installed a 14' long piece of 1.5" schd#40 steel pipe, by welding some tabs to it and screwing up into the bottom of the platform. This pipe was two-fold in purpose, it acted as a support across the seam of the two stress skins, and it acted as a tubular track for the lifting, dropping device.
For the dropping device I used two transmission jacks from which I removed the screw and replaced it with a 2.73 inch diameter 6"throw pnuematic cylinder. On the top of the transmission jack I removed one of the bolts and replaced it with all-thread and made an axle for a 4" groved polyurethanecaster. this caster rode the pipe as a guide. The whole system worked really well and I only had one problem, when the stage crew had reset the trick after a show, sunday night, then come back for the show on Tuesday night, without bothering to re-fill or re-charge the pnuematics. The rest of the gags were all solenoid actuated tricks like two roofs falling a signpost collapsed a window fell out of its frame oh and my favorite of all which I need to submit pictures for was the dropping of a "light-bar" < not my description> where I had to build my self two quick release clamps from solenoids and vice-grips, < and it worked ! >
That sounds really effective. I have not yet used any pnuematics in any of my sets, I pretty much rely on mechanical means.
Our stage was basically a hinged 12' x8' platform with the downstage sitting on 4 wheeled 4x6 legs. We attached a long brace to the axle that ran through the legs, and from behind the "Carol Set", we simply unpinned the brace and gave a pull, dropping the stage 18", and scaring the hell out of the first 10 rows.
Our challenge was that the "theater" sat almost 15' away from the edge of the Carol Stage, so we had to sit the actor with the punchbowl on a wheeled table, which rolled off the stage, across the stage on onto the lap of the Inspector.
It's a really fun show to do, especially because of all the gags.