garageFab.cc

I finally updated the plotter design to use new linear motion components. While at it, I moved few things around, like belts to the outside; and now the plotter has 17"x11" work area. I have not assembled/tested it yet, but I think most parameters from the older version still apply. The BoM is also compete ($290 if built from scratch), the files are at http://contraptor.svn.sourceforge.net/viewvc/contraptor/trunk/contraptions/xy-plotter/

There is an interesting quirk about belt drives in Contraptor. Normally, the distance between two pulleys is equal to the length of the rail + 1". The circumference of the pulley is 2".  If the distance between the pulleys is p, then the belt length = p*2+2. So, for example, belt drive built on 18" rail uses the belt length = (18+1)*2+2 = 40". However, I was dismayed to find out that not every belt length is commercially available. Such is the case for 24" rail which needs 52" long belt. I could not find it anywhere, so I had to extend the pulley 1 inch beyond the rail so that I could use 54" long belt, which was available at SDP/SI. This is clearly visible on the left of X axis in the rendering of the plotter. I guess it's something to keep in mind when designing belt drive stages..