Blocks on moving platform not following correctly

When placing more than 10 or 20 blocks on a moving platform, the blocks will not stay nicely still on the platform.
They ‘jitter’ and eventually slide off the rear end of the platform.

This can be reproduced by creating a new project, create a blueprint with a moving platform(cube) using the ‘move component to’ function, or any other way to move it (horizontally). Then place some cubes on it.

In UE 4.13 everything works fine. I have noticed the issue in both 4.14.0 and 4.14.1.

Changing physics sleep settings and sensitivity on the blocks and the platform does not appear to influence the issue.


Hi B V,

Thank you for the report. I was able to reproduce this behavior and I’ve created JIRA UE-39791. I’ll developers will be investigating further. Follow that link to monitor the bugs progress and feel free to vote.



B V,

After investigating this a bit more, it seems like the problem is that the collisions set up for your cube may not be correct.

When testing, we noticed that there were only 3 contacts being generated for the collision. This meant that the cube would continually rock back and forth (which was the cause of the jitters). Simply rotating the cube so it landed on a different face would fix the issue.

We also didn’t observe this behavior with the built in editor cube, which also uses a Convex shape (instead of a simple Cube shape).

The first thing to try would be to regenerate collisions for your mesh. If that doesn’t work, you can go to your project settings and enabling PCM under physics.

It’s possible that what you’re seeing is an issue that was masked by a deprecated code path in PhysX that has decayed in 3.4.

Jon N.

Hi Jon,

Thanks for looking into this issue.
I highly doubt the problem is related to how the collision is set up, because the problem can be reproduced by creating a new project and creating basic StaticMesh cubes and simply enabling physics. The problem also appears when using the StarterContent block ‘SM_CornerFrame’ with physics enabled.
Also, your staff member TJ Ballard seems to have reproduced the issue with only my text instructions (i have not sent any project files). So incorrect setup of the collision would seem very unlikely.
I have now also tested with PCM enabled and tested in UE version 4.14.2, but the problem remains unchanged.

Thank you,

Hey B V,

We are looking into this again and hope to let you know more soon.

In the meantime, could you try the PCM setting that Jon mentioned above. Let me know if it helps with the issue at all.

I’ve tried enabling PCM (Settings > Project Settings > Engine > Physics > Simulation > Enable PCM), but this hasn’t had any effect on the problem.
Let me know if I can help out in any way.

Okay, I’m seeing that on this side too. I’ve reopened the bug report and the devs will be looking into this further. We’ll update here when there is more info.