[dtengineering]

First off... that's a beautiful machine. I suspect you're asking the question from a safety perspective first, and... were I inspecting the machine, I'd have no problem passing it as it stands without additional coverings on the arm frame. I do not speak for other inspectors, however... they may see a hazard I have missed.

I do, however, see a wonderful opportunity to put some lightweight coroplast, plywood, thin polycarbonate, or "twinwall" type corrugated polycarbonate over the gap and use it as a place to prominently display the name of your team and your sponsors. (We will be looking for that, remember! Rule R13) A thin sheet of aluminum could do the trick, too, and you do seem to have access to some nice machining facilities.

If you've got a wee bit left in your weight limit, I see those sides as the perfect place to add the "bling" that turns this robot from looking good to looking GREAT!

Jason