WorldViz User Forum  

Go Back   WorldViz User Forum > Vizard

Reply
 
Thread Tools Rate Thread Display Modes
  #1  
Old 10-31-2012, 11:29 AM
mhead10 mhead10 is offline
Member
 
Join Date: Mar 2012
Posts: 40
Physics: Ball Bounces Unexpectly Based Upon Size + Ring Collision Shape

I have modified an example physics script to try and determine why my script isn't working. I want my "ball.wrl" to remain stationary on the ground (as it would in real life because gravity keeps it on the ground). However, this only seems to work if the ball scale is very small (0.1,0.1,0.1) versus large (10,10,10). If the scale is large, the ball takes an initial bounce and then remains stationary. I've set ball bounce equal to zero, so I'm not sure why the ball bounces. (I realize the "bounce" effect scales with size, but I would like to get rid of the initial effect from the beginning).

Code:
#meshing
import viz
import vizact
import vizcam
viz.phys.enable()   # Enable physics

viz.setMultiSample(4)
viz.fov(60)
viz.go()

#Change navigation style to pivot
cam = vizcam.PivotNavigate(center=[0,0,0], distance = 15)
cam.rotateUp(45)
cam.rotateRight(0)

#Add the object that will do the grabbing
hand = viz.addChild( 'marker.wrl' )
hand.setPosition( [-0.5, 1.8, 2.5] )

viz.phys.setGravity(0,-9.8/6,0) #Half Gravity
ground = viz.add('tut_ground.wrl')  # Add ground
ground.collidePlane()   # Make collideable plane

logo = viz.add('logo.wrl',pos=[0,1,6]) # Add logo
logo.collideMesh(bounce=1.5) # Collide and make it bounce a bit

link = None #The handle to the link object


for x in range(10):
    for z in range(10):
        ball = viz.add('white_ball.wrl',pos=[-.5+.1*x,2.5+.1*z,6],scale=[.5,.5,.5])
        ball.collideSphere()


x = viz.add('ball.wrl', pos =(0,0,0), scale=[1,1,1])
ringPhys = x.collideSphere(bounce = 0)   # Define x's physical properties

#Grab or let go of the ball
def toggleLink():
    global link
    if link:
        #If link exits, stop grabbing
        link.remove()
        link = None
    else:
        #If no link, grab the ball with the hand
        link = viz.grab(hand, x)

vizact.onkeydown(' ',toggleLink)


#Setup keyboard control of hand and ball
vizact.whilekeydown(viz.KEY_UP,hand.setPosition,[0,vizact.elapsed(1),0],viz.REL_PARENT)
vizact.whilekeydown(viz.KEY_DOWN,hand.setPosition,[0,vizact.elapsed(-1),0],viz.REL_PARENT)
vizact.whilekeydown(viz.KEY_RIGHT,hand.setPosition,[vizact.elapsed(1),0,0],viz.REL_PARENT)
vizact.whilekeydown(viz.KEY_LEFT,hand.setPosition,[vizact.elapsed(-1),0,0],viz.REL_PARENT)

vizact.whilekeydown('w',hand.setEuler,[vizact.elapsed(90),0,0],viz.REL_PARENT)
vizact.whilekeydown('s',hand.setEuler,[vizact.elapsed(-90),0,0],viz.REL_PARENT)
vizact.whilekeydown('d',hand.setEuler,[0,vizact.elapsed(90),0],viz.REL_PARENT)
vizact.whilekeydown('a',hand.setEuler,[0,vizact.elapsed(-90),0],viz.REL_PARENT)
Secondly, if I change the ball collision shape to mesh, gravity no longer affects the ball. I'm guessing the documentation is defining gravity as a force (link), "Collide mesh objects are unaffected by forces and can only provide a solid collision area for other objects." Therefore, is there a way I can have a ring shape (just like a wedding ring) be a collision shape and be affected by gravity. I need to have the ring be dropped around a peg (capsule collision shape or mesh of cylinders) without having the ring go through the peg (only around it).

Thanks for your time!
Reply With Quote
  #2  
Old 11-01-2012, 07:44 AM
mhead10 mhead10 is offline
Member
 
Join Date: Mar 2012
Posts: 40
I see the ring question has been answered here.

However, I would still benefit from someone helping with my first question. How do I get rid of initial "bounce" and "wobble" of a node?

Here's another example to demonstrate my question:
If I have a ball sitting atop a hole which is slightly smaller than the diameter of the ball, and gravity or a force is enabled, my ball doesn't "sit still" atop the hole. Rather, it wobbles around the hole for several seconds until it eventually slows down and sits atop the hole. If the collision plane and ball is perpendicular to gravity, shouldn't the ball's position remain initially constant and not wobble around?

My attached pictures shows one of the balls wobbling around the hole instead of its position remaining constant.

Code:
viz.add('shaft.dae', pos = (0,0,0))
base = viz.add('base.dae', scale=[1,1,1],euler=[0,0,0], pos = (-2.5,0,-2))
base.texture(pic_base)

# add spheres
sphere1 = viz.addChild('ball.dae', viz.WORLD, pos = (-.65,.17,.84), scale=[0.4,0.4,0.4],euler=[0,0,0], texture=(pic_sphere))
sphere2 = viz.addChild('ball.dae', viz.WORLD, pos = (-.65,.2,-.19), scale=[0.4,0.4,0.4],euler=[0,0,0], texture=(pic_sphere))
sphere3 = viz.addChild('ball.dae', viz.WORLD, pos = (-.65,.2,-1.18), scale=[0.4,0.4,0.4],euler=[0,0,0], texture=(pic_sphere))
sphere4 = viz.addChild('ball.dae', viz.WORLD, pos = (-1.64,.2,.82), scale=[0.4,0.4,0.4],euler=[0,0,0], texture=(pic_sphere))
sphere5 = viz.addChild('ball.dae',viz.WORLD, pos = (-1.64,.2,-.19), scale=[0.4,0.4,0.4],euler=[0,0,0], texture=(pic_sphere))
sphere6 = viz.addChild('ball.dae', viz.WORLD, pos = (-1.64,.2,-1.18), scale=[0.4,0.4,0.4],euler=[0,0,0], texture=(pic_sphere))

base.collideMesh() 
viz.phys.setGravity(0,-10,0) #world gravity
sphere1.collideSphere(bounce = 0)  
#sphere1.applyForce([0,0,-2])
#ringPhys = sphere2.collideSphere(bounce = 0)  
#ringPhys = sphere3.collideSphere(bounce = 0)  
#ringPhys = sphere4.collideSphere(bounce = 0)  
#ringPhys = sphere5.collideSphere(bounce = 0)  
#ringPhys = sphere6.collideSphere(bounce = 0)  

#linking
link = None #The handle to the link object

#Grab or let go of the ring
def toggleLink():
	global link
	if link:
		#If link exits, stop grabbing
		link.remove()
		link = None
	else:
		#If no link, grab the circle with the shaft(parent + grasper tip (children))
		link = viz.grab(shaft, sphere1)
vizact.onkeydown(' ',toggleLink)

vizact.whilekeydown(viz.KEY_UP,shaft.setPosition,[0,vizact.elapsed(1),0],viz.REL_PARENT)
vizact.whilekeydown(viz.KEY_DOWN,shaft.setPosition,[0,vizact.elapsed(-1),0],viz.REL_PARENT)
vizact.whilekeydown(viz.KEY_RIGHT,shaft.setPosition,[vizact.elapsed(1),0,0],viz.REL_PARENT)
vizact.whilekeydown(viz.KEY_LEFT,shaft.setPosition,[vizact.elapsed(-1),0,0],viz.REL_PARENT)
Attached Thumbnails
Click image for larger version

Name:	wobble.JPG
Views:	399
Size:	58.7 KB
ID:	544  
Reply With Quote
  #3  
Old 11-01-2012, 03:36 PM
Jeff Jeff is offline
WorldViz Team Member
 
Join Date: Aug 2008
Posts: 2,460
If modifying the physics properties of the object is not working the way you expect, you could try removing all forces on the ball once it reaches a certain position. To do that, use the node3d.reset command.
Reply With Quote
  #4  
Old 11-02-2012, 02:44 PM
mhead10 mhead10 is offline
Member
 
Join Date: Mar 2012
Posts: 40
Jeff, thanks for your reply.

I think I found the problem (for the 2nd example) was because the ball's center was at (0,0,0) and the position was initially (0,0,0) as well. Therefore, the ball was initially colliding with the ground and thus it pops or bounces up.

If I moved the initial position to (0,.25,0), then I didn't notice a bounce.

Thanks again!
Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
collision with physics enabled joeymax Vizard 2 04-17-2008 03:49 PM


All times are GMT -7. The time now is 03:44 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Copyright 2002-2018 WorldViz LLC