We propose a continuation of experiment RB910427, for EMU after the station upgrade. We would like to use muon spin relaxation spectroscopy to probe the spin dynamics in the B-site ordered double perovskite Ba2YMoO6 and one or two related systems, with the non-magnetic Y replaced by Eu or Yb, or with Ba (partially) replaced by Sr. All evidence to-date suggests that the Mo5+ S=1/2 t2g spins do not freeze down to 1.4 K despite a sizeable exchance interaction of the order of 100 K. Only a very small degree of site disorder has been detected in these systems and at all temperatures the symmetry remains cubic, which implies the systems are 3D spin/orbital liquids. There is currently a strong interest in 3D magnetic systems, for which theoretically very little is known. MUSR experiments might be key in understanding the so far mysterious behaviour of this group of compounds.