Suggestions --> Ceiling Mounted Rail System

SRLM

What about making a gantry crane that hangs from the central column? If you make it so that it can swing all the way around the column then you can access almost the entire classroom with just one crane. A second crane would allow you to get everywhere. Plus, the crane would use the (presumably) strong pillar for support, and you wouldn't even have to drill any holes to fasten it.

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Scope

Oh, I dunno . . . the more I think about this, the more I'm starting to like the wheeled, floor roaming version.

Bocephus

That pic is like what I was suggesting with the rail encompassing the columns, except with only one telescoping arm traveling around and extending to any desk location with a basket on the end to collect and deliver papers. Looks cool!

Scope

I planned to have only one arm - the sketch was a study to get an idea how the arm would maneuver around the corners. I should have mentioned that - it's a bit confusing.

Graham Stabler

Spiral's idea is a good one (beat me too it!) and the mathematics involved is only Pythagoras, You could have two systems of this type with a short conveyor on the desk between the posts, or better, two short slides, one sloping in each direction for the pass over.

However the problem with most parallel kinematic machines is the working envelope, to get to all the desks in one half of the room you will need to have 4 strings, one in each corner, this would not be the case if the strings were rods able to push.

I've done a little on parallel kinematics, take a look at my page for some ideas. There is also a pdf with some details, though focussed on CNC it contains the mathematics for a 2-axis string bot:

www.indoor.flyer.co.uk/kinematics.htm

Oh and another machine I actually made:

www.youtube.com/watch?v=QMJE7o_3aFo

Cheers,

Graham