PGS Solver Migration Feedback Request

Similar to NWSpacek, I am having issues with vehicles acting strangely, mostly when a player jumps out of a seat to hit the roof of a car it can cause the car to fly under the map or into space.
There is also the issue of walking through walls, a player can use shift lock in a corner to go through thick walls, but it gets better in that you don’t need to use it if you want to go through walls that are 0.4 studs or less in thickness you just walk straight at them and wait until you’re through. This behaviour did not happen in spring solver but now I am stuck with PGS because I started using some new constraints in the game.


I was attempting to design an obstacle course with moving platforms using contraints. I can’t use distributed physics since multiple players may be on the part at once meaning the server must control them. The problem is, they appear jittery and don’t move at a constant speed (despite the server telling them to).

This was less of an issue with the old solver for me. I’ve actually started using my own system now though…


I believe @TwentyTwoPilots had something to say about this about Car Wheels earlier! Pinging him to alert him.

Old but still relevant annoyance I have. I know how to solve it but doing so can be tedious

This is how it’s setup in a nutshell. I was informed that this creates some kind of over-constraint system and it can’t be done which is really frustrating. To fix the problem, I have to settle on the solution 2 and separate the parts

I’d rather just use the old system and avoid the hassle. I find it more ‘accurate/reliable’ in terms of marble contraptions. The older system is much more reliable and easier to work with.


Thanks for your feedback. Could you send me this place? @anon80475429

Could you send me a simple repro where the character tunnels through walls? Thanks! @pauljkl

Seems to happen in large, slowish servers, not sure how simple a repro could be. You just face directly at a wall and walk forwards for the 0.4 stud thickness.
If you want to get through thicker walls you just stand facing a corner, walking into the corner, point your camera away and use shift lock to fling yourself through the wall


In my experiments with PGS and spring, it appears PGS scales similarly to spring, i.e. the calculations are as time consuming, so there’s no real speed benefit from using PGS. If I knew that PGS could get me several more train cars for a given framerate, for example, I could be convinced to use it in more projects.

EDIT: clarification on my last post, if you wanted to know:

The main undesirable behavior in spring physics is the state where hinged objects like wheels begin to fly around like a swarm of angry bees. PGS has this too, but PGS also has other things, unfortunately.


We just released a fix for the jumping off edges problem under PGS


The big main issue i’m having is the Cylinder instability, it kinda happends with Balls too, when going over brick seams it jumps, and it goes back to the over reaction of PGS when intersecting with other parts before mentioned.
With cylinders it seems to be almost unplayable at high speeds, balls seem to handle it better but it still happends.


I second this, I’ve refrained from converting my work to PGS in hopes of this being fixed as it makes driving entirely unenjoyable. The issue is especially noticeable at Vehicle Simulator.

If you have a high walkspeed, maybe around 50 or so, and you attempt to jump over uneven ground while running, you will jump up almost vertically every time. It gets very annoying in games like Miners Haven.

I’ll upload a gif later to show what I mean.

Do you mean that when you jump the character looses its forward momentum? It would be better if you send us an rbxl place with repro steps. Thanks

So this was where I found the problem.

Yes, you lose a lot of momentum if you have a high walkspeed.


Attached is a small repro place I made just to show what I mean.

test.rbxl (21.0 KB)

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So we fixed some of the issues with jumping (under PGS). Are you still seeing this momentum loss?


@Younite I updated the repro file you gave to print out character horizontal velocity so it’s easier to see the change in momentum:

test.rbxl (22.4 KB)

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Can’t really reproduce any differences. Is it something you can see while climbing that wedge?

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In both PGS and the legacy solver, I experienced the same behavior climbing the wedge/mountain and falling off of them: decreased momentum going up because the character is colliding with a wall and then being pushed up to climb, but no decrease in momentum when landing from the fall at the end.

I can’t speak for Younite because maybe he meant something else, but since both the legacy/PGS solvers exhibit the same behavior when climbing and landing from a fall, I would assume issue resolved.

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Ok thanks @EchoReaper.

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If you can, please file a separate bug report for this issue. It seems to be unrelated to the PGS vs Legacy discrepancies but might be a honest problem that might get looked at by the avatar team.

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