Add approximate Mini Cheetah URDF and example in pybullet

Thanks to Sangbae Kim and Donghyun Kim at the MIT Biomimetics Robotics Lab

examples/pybullet/gym/pybullet_envs/examples/mini_cheetah_test.py

@@ -0,0 +1,23 @@
+import pybullet as p
+import pybullet_data as pd
+import time
+
+p.connect(p.GUI)
+p.setGravity(0,0,-9.8)
+p.setAdditionalSearchPath(pd.getDataPath())
+floor = p.loadURDF("plane.urdf")
+startPos = [0,0,0.5]
+robot = p.loadURDF("mini_cheetah/mini_cheetah.urdf",startPos)
+numJoints = p.getNumJoints(robot)
+p.changeVisualShape(robot,-1,rgbaColor=[1,1,1,1])
+for j in range (numJoints):
+	p.changeVisualShape(robot,j,rgbaColor=[1,1,1,1])
+	force=200
+	pos=0
+	p.setJointMotorControl2(robot,j,p.POSITION_CONTROL,pos,force=force)
+dt = 1./240.
+p.setTimeStep(dt)
+while (1):
+  p.stepSimulation()
+  time.sleep(dt)
+