Ball physics breaking on non-PGS games

Bug Reports Engine Bugs
#1

Beginning within the past week or so, all of the vehicles’ wheels in Ultimate Driving have been inexplicably sinking into the ground causing noticeable handling issues and instability. My vehicles use ball parts with cylindrical meshes for wheels. The sinking is especially prominent on the fire engine:

1017×394 116 KB

This seems to occur for all vehicles to varying extents 100% of the time. I couldn’t seem to reproduce it reliably on an empty baseplate, but I’ve not released any updates within the time frame of this issue appearing so I doubt it’s something I’ve done. This is specifically occurring on non-PGS games, I’m not using PGS because wheel physics have never had this problem fixed.

7 Likes
#2

My friend JohnDrinkin noticed this as well. He says it’s all based on weight in spring physics, and he made a simple repro:

WeightTest.rbxmx (28.4 KB)

2 Likes
#3

Took me a long time to track the issue down. I did a huge refactor on Collision Detection pipeline, and apparently made an accidental change that wasn’t behind a switch, which broke some important step-to-step caching. :frowning:

I’m patching our release candidate ASAP, so the fix will be in on Tuesday night. Apparently this has been around since 298 :frowning:

6 Likes
#4

Looks like this has been fixed. Thanks!

1 Like
#5

Thanks for the follow up. Shouldn’t have broken it in the first place : (

Word of advice for future engineers:

  • If your physics unit tests suddenly become SLIGHTLY less repeatable (end-positions for falling parts change a tiny bit), it’s probably not fine.
  • You should investigate, even if the end result looks fine.
#6

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