Second Life Forums Archive - Odd collision behavior dropping things onto cylinders

Taeko Hykova

Error: Null Pointer

Join date: 15 Jun 2008

Posts: 2

02-10-2009 16:58

I was in a building contest last night and decided to be really gutsy and do some physics scripting. I was trying to build a Bean machine-type toy (think bagatelle or Plinko) where a physical temporary ball gets rezzed and dropped into the machine, it bounces off lots of little cylindrical pegs, and it eventually falls into one of several bins at the bottom of the machine.

Many times when balls got dropped into the machine, even when I gave the balls some slight random drop location offset, the spherical balls would get stuck on top of cylindrical pegs. Other balls could collide with them and knock them off, but there were always a few balls hung up in the machine. Before I added that slight entropy to the device, the balls stacked up on top of one another on top of the top cylindrical peg!

Any ideas what could have been causing that weird behavior, and how I could have fixed it so that the spheres bounced off of the cylinders nicely? (I'm thinking now it may have been a bounding box issue and that I should have rotated cylinders around the z-axis as a hack, but I really have no idea.)

For the record, I am NEVER using the physics engine in a building contest again. It's like juggling knives in an amateur ball-juggling contest.

Jesse Barnett

500,000 scoville units

Join date: 21 May 2006

Posts: 4,160

02-10-2009 18:31

Hint #1: Round balls in SL are not round.

Hint #2: LOD

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Lee Ponzu

What Would Steve Do?

Join date: 28 Jun 2006

Posts: 1,770

02-10-2009 18:44

You just know the wrong physics...

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Lazink Maeterlinck

Registered User

Join date: 8 Nov 2005

Posts: 332

02-10-2009 19:34

Yes, it's a bounding box issue, as Jesse said, Round balls are not round, nor are cylinder or anything else. As for a solution, several, but I'm not a physics engine expert, so don't know if your spinning of the cylinder would work, but I would think that a colliison event with a peg, that gives the ball a little "boost" would work as well.

Osprey Therian

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Join date: 6 Jul 2004

Posts: 5,049

02-10-2009 19:50

http://www.youtube.com/watch?v=sZq9k_DMoiA

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Jesse Barnett

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Join date: 21 May 2006

Posts: 4,160

02-10-2009 20:03

And you can also make more then one copy of the ball and put them together, each with a different rotation. This makes it so that the flat spots are not all aligned and the ball is "rounder".

Easy way to see the scope of the problem and experiment is to roll a ball on a ramp.

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Jesse Barnett

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Join date: 21 May 2006

Posts: 4,160

02-10-2009 20:14

Create a sphere and make it large, maybe 5 meters in all axis and then go into edit/preferences/Graphics and check the "custom" box, turn "objects" Mesh Detail all the way down and look at the sphere.

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SuezanneC Baskerville

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Join date: 22 Dec 2003

Posts: 14,229

02-10-2009 20:52

Would twisting a sphere change its collision behavior?

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Odd collision behavior dropping things onto cylinders
Taeko Hykova Error: Null Pointer Join date: 15 Jun 2008 Posts: 2	02-10-2009 16:58 I was in a building contest last night and decided to be really gutsy and do some physics scripting. I was trying to build a Bean machine-type toy (think bagatelle or Plinko) where a physical temporary ball gets rezzed and dropped into the machine, it bounces off lots of little cylindrical pegs, and it eventually falls into one of several bins at the bottom of the machine. Many times when balls got dropped into the machine, even when I gave the balls some slight random drop location offset, the spherical balls would get stuck on top of cylindrical pegs. Other balls could collide with them and knock them off, but there were always a few balls hung up in the machine. Before I added that slight entropy to the device, the balls stacked up on top of one another on top of the top cylindrical peg! Any ideas what could have been causing that weird behavior, and how I could have fixed it so that the spheres bounced off of the cylinders nicely? (I'm thinking now it may have been a bounding box issue and that I should have rotated cylinders around the z-axis as a hack, but I really have no idea.) For the record, I am NEVER using the physics engine in a building contest again. It's like juggling knives in an amateur ball-juggling contest.
Jesse Barnett 500,000 scoville units Join date: 21 May 2006 Posts: 4,160	02-10-2009 18:31 Hint #1: Round balls in SL are not round. Hint #2: LOD _____________________ I (who is a she not a he) reserve the right to exercise selective comprehension of the OP's question at anytime. From: someone I am still around, just no longer here. See you across the aisle. Hope LL burns in hell for archiving this forum
Lee Ponzu What Would Steve Do? Join date: 28 Jun 2006 Posts: 1,770	02-10-2009 18:44 You just know the wrong physics... _____________________ So many monkeys, so little Shakespeare.
Lazink Maeterlinck Registered User Join date: 8 Nov 2005 Posts: 332	02-10-2009 19:34 Yes, it's a bounding box issue, as Jesse said, Round balls are not round, nor are cylinder or anything else. As for a solution, several, but I'm not a physics engine expert, so don't know if your spinning of the cylinder would work, but I would think that a colliison event with a peg, that gives the ball a little "boost" would work as well.
Osprey Therian I want capslocklock Join date: 6 Jul 2004 Posts: 5,049	02-10-2009 19:50 http://www.youtube.com/watch?v=sZq9k_DMoiA _____________________ http:www.atomic-raygun.com Combat Cards in Europa [url=http://slurl.com/secondlife/grignano/118/116/]The Photography Studio in Grignano[/url] Mud! Mud! Glorious mud! Nothing quite like it for cooling the blood. So, follow me, follow, down to the hollow, And there let us wallow in glorious mud. Flanders and Swan
Jesse Barnett 500,000 scoville units Join date: 21 May 2006 Posts: 4,160	02-10-2009 20:03 And you can also make more then one copy of the ball and put them together, each with a different rotation. This makes it so that the flat spots are not all aligned and the ball is "rounder". Easy way to see the scope of the problem and experiment is to roll a ball on a ramp. _____________________ I (who is a she not a he) reserve the right to exercise selective comprehension of the OP's question at anytime. From: someone I am still around, just no longer here. See you across the aisle. Hope LL burns in hell for archiving this forum
Jesse Barnett 500,000 scoville units Join date: 21 May 2006 Posts: 4,160	02-10-2009 20:14 Create a sphere and make it large, maybe 5 meters in all axis and then go into edit/preferences/Graphics and check the "custom" box, turn "objects" Mesh Detail all the way down and look at the sphere. _____________________ I (who is a she not a he) reserve the right to exercise selective comprehension of the OP's question at anytime. From: someone I am still around, just no longer here. See you across the aisle. Hope LL burns in hell for archiving this forum
SuezanneC Baskerville Forums Rock! Join date: 22 Dec 2003 Posts: 14,229	02-10-2009 20:52 Would twisting a sphere change its collision behavior? _____________________ - So long to these forums, the vBulletin forums that used to be at forums.secondlife.com. I will miss them. I can be found on the web by searching for "SuezanneC Baskerville", or go to http://www.google.com/profiles/suezanne - http://lindenlab.tribe.net/ created on 11/19/03. Members: Ben, Catherine, Colin, Cory, Dan, Doug, Jim, Philip, Phoenix, Richard, Robin, and Ryan -

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Odd collision behavior dropping things onto cylinders