problem in drag force using

We are trying to implement the drag force in a simulation with two different density materials, but when simulating the both spheres fall in the same velocity. Anyone knows what is wrong in our code?

from yade import pack, plot, qt, utils, ymport
import numpy

Styrofoam=CohFrictMat(density=23)
idStyrofoam=O.materials.append(Styrofoam)

steel=CohFrictMat(density=7900,young=1.96e11)
idsteel=O.materials.append(steel)

O.bodies.append([
   sphere(center=(0,2,100),radius=.5,material=idStyrofoam,color=(1,1,0)),
   sphere((0,0,100),.5, material=idsteel,color=(1,0,1))
])

O.engines=[
   ForceResetter(),
   InsertionSortCollider([Bo1_Sphere_Aabb(),Bo1_Facet_Aabb()]),
   InteractionLoop(
      [Ig2_Sphere_Sphere_L3Geom(),Ig2_Facet_Sphere_L3Geom()],
      [Ip2_FrictMat_FrictMat_FrictPhys()],
      [Law2_L3Geom_FrictPhys_ElPerfPl()]
   ),
   NewtonIntegrator(gravity=(0,0,-9.81),damping=0.05),
   DragEngine(ids=[0,1],Cd=0.2, Rho=1.225),
]

O.dt=.05*PWaveTimeStep()

thank's for helping