For our team’s bot, we have a 4 bar dumper design. I was thinking about using a polycarbonate box to stabilize the lift in the center. If this box had 4 sides of polycarbonate and 2 sides of C channel, would it stay rigid enough for this application?
I think a picture would help tremendously :P, since I am not quite sure what you mean by a “box to stabilize the lift”.
However, there a couple things you should consider when thinking about using polycarb. Firstly, polycarb is pretty bendy if it’s not attached to metal/something rigid along the sides (this is something you probably know already). If we’re talking something that’s like 2 or 3 inches square, you might be able to get away with just securing the polycarb on 1 or 2 sides, but if it’s much bigger than that (as the idea of a “box” suggests), then you will definitely need to make sure the polycarbonate is screwed in on 3 or even 4 sides of the piece of plastic.
Another thing (that you probably knew already :P) is that there’s the 1’ by 2’ limit on polycarb, so unless your box is pretty tiny, I don’t know if you’ll be able to pull it off.
Yeah, a picture would help. Anyway, if one sheet was bolted to the back, one to the front (4 screws each) I know the lift would still have sideways flex. On the top and bottom of the C-channel I was thinking about also using polycarbonate. (If I find an elegant way to attach it) Although I may just make the lift a bit smaller and use 2*25 in place of the top/bottom C channel. (But I would rather not, and the current spacing is just under 29 holes between the 2x10s)
I think I see what you mean now. If I understand correctly, you’re planning on using polycarbonate for an essentially “structural” purpose, to hold the sides of your lift together?
If that’s the correct interpretation, then I would firstly recommend that you just use a cut-to-size C channel. While it might seem like a bit of a hassle to get the 29 hole long piece of metal, I think it will be the easiest solution overall.
However, that isn’t to say that polycarb absolutely 100% won’t work - it can, and has. Check out 2Z from Skyrise:
They used multiple strips of polycarbonate mounted in various configurations to keep their lift together, and so if you tried something similar, you might be able to pull it off.
I hope that helps! 
Thanks for the thoughts! I would go for the 29 hole metal, but I am not exactly a fan of cutting metal to odd lengths. I’ll give the polycarbonate a try and if it doesn’t work, no harm done – as far as I remember it’s far cheaper than metal.
The main reason the poly has flex is its plane form. If you put folds in the sheet using a brake, it would be far more rigid.