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Bug in physics simulation

I created room with 4 walls and 50 physical balls that have locked Z-axis. Walls and balls are made from custom "ideal material" with friction=0;restitution=1;Balls have initial speed. And i faced next problem-sometimes(not always) balls lose all their speed when they hit corners or wall. So more and more balls getting stuck,and 10 minutes later room has no moving balls(ideal room with no friction and full restitution must have it's ball moving forever,isnt it?). So what is wrong? Is there any way to make balls moving forever without applying force/impulse/speed to them? alt text

Product Version: UE 4.7
ballissue.png (256.1 kB)
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asked May 23 '15 at 10:24 PM in Bug Reports

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avatar image Samantha Sutton ♦♦ STAFF May 27 '15 at 04:10 PM

Hey WitcherSanek,

I have set up a room similar to yours and have included balls that bounce around the room. None of the balls added into the level were getting stuck in the corners of the room. I locked the position to the z-axis and tried, none were stuck. I then kept the locked position on the z-axis and added the lock rotation to the z-axis as well, and none were stuck. How often does this happen? Does it typically happen mostly with the smaller sized balls than the larger sized ones, or does it not matter?

Also, would you be able to show me screenshots of how the ball actor is set up, or perhaps provide it to me to look at? By the way, I'm working in 4.8.0 Preview 3 currently.

Looking forward to hearing back from you, thanks!

avatar image WitcherSanek May 27 '15 at 07:48 PM

Hello. Balls of any size are getting stuck in my project. I tried 4.7.6 and 4.8 P2 versions. Here's screenshots of ball settings and ball material settings.alt text

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avatar image Samantha Sutton ♦♦ STAFF May 27 '15 at 08:49 PM

Hey Witcher,

Thank you very much for providing me the screenshot of your physical material settings. I've set mine up exactly like yours, using 4.8.0 Preview 4. I have not been able to get my project to display the same issue that yours is experiencing, where the balls are sometimes stuck in the corners of the walls.

Have you attempted to set this up in the newest release of the engine with the same reproduction, where they're stuck in the corners? I know that you said you were able to produce the same in 4.8.0 Preview 3, I was wondering if you're using the same project, or if you set up another?

If setting up another project like this also displays the same behavior, would you mind zipping the project for me and submitting a link either here (if you don't mind the public viewing it) or you can provide it to me in a link on the forums, through a private message. You should be able to find me by searching for 'Samantha Sutton'.

Thank you!

avatar image WitcherSanek May 27 '15 at 09:14 PM

Here's my project. Balls are keep getting stuck no matter what i try to do. http://www.filedropper.com/particles47 I tried 4.7.6 and 4.8P3 versions

avatar image Samantha Sutton ♦♦ STAFF May 28 '15 at 05:14 PM

Hey WitcherSanek,

Thanks for providing me with your project. Unfortunately, I wasn't able to open your project in 4.7.6 or 4.8 Preview 4, but I was able to take the content from it and place it into mine. I set it up accordingly based on your project, except my project area is quite larger. I let it run for a while and the balls did not get stuck in the corners of the room. Any time one of the balls stopped moving, another would hit it and it would set it off again and they'd continuously bounce around the screen. Make sure that you've added the physical material onto the objects. When I moved over the content, they weren't set up that way, but since I couldn't open your original file, I can't say for certain if you set it up that specific way or not.

I am not sure what is causing the issue with your project however, have you tried adding blocking volume around the parameter to see if that helps the balls bounce off more easily? I have a blocking volume as a ceiling and one wall in my project, and they do bounce off of that just as well as the static mesh walls.

Looking forward to hearing back from you, thank you!

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1 answer: sort voted first

Seems like setting "Bounce threshhold velocity" in project settings to "0"(it was 200 at startup) fixed my issue.

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answered May 31 '15 at 12:02 PM

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avatar image Samantha Sutton ♦♦ STAFF Jun 01 '15 at 02:05 PM


I'm glad you were able to figure out the issue you were running into. If you have any further questions, please let us know and we'll assist you further.

I hope you have a wonderful week! :)

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