def getSample(wellx,welly,rack,grid,pos):
plate=Plate.lookup(grid,pos)
if plate is None:
plate=Plate(rack,grid,pos)
wellname="%c%d"%(ord('A')+welly-1,wellx)
well=plate.wellnumber(wellname)
s=Sample.lookupByWell(plate, well)
if s is None:
s=Sample("%s.%d.%d.%d" % (rack, grid, pos, well), plate, well)
if grid==3:
s.volume=20000 # Troughs
else:
s.volume=0
return s
