Probelm about reset_manip_pose() for PR2

[ktro2828]

when I call reset_manip_pose() for PR2, torso link dosen't work right.

import skrobot
from skrobot.models import PR2
from skrobot.interfaces import PybulletRobotInterface

robot = PR2()
interface = PybulletRobotInterface(robot)

I added following code

interface.force = 10000

then it worked!