Switching all games to the PGS Physics Solver next week (March 4th, 2019)

You have had over 3 months to prepare. In addition to this, I’m pretty sure a banner appeared in Studio warning you to use the new solver if you weren’t already.


The banner would only appear until you clicked the X, then in all future Studio instances it would only appear when Studio is loading a game and the viewport wasn’t rendering correctly. (i.e: only for a frame or two).

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Is there still going to be an option where we can still use the old physics solver with approval? Conveyors don’t work with the new PGS solver and the movable parts phase through anchored parts often on map locations very far from (0,0,0). Those bugs were there 1-2 years ago when I first tried to convert. A year later it is still not solved. Roblox should at least fix the pgs physics solver before forcing everyone to switch. This is literally going to kill the aviation and transportation industry.

My game is literally broke now… https://www.roblox.com/games/172205561/Hyperloop-Simulator-Lasagna-Pod


This does not sound like a valid reason to me. If you dismissed the banner, you already saw it and were aware that this change was about to happen. If you didn’t pay attention to what the banner said, that would be on you and not on Roblox.


Yeah, there should be no reason to delay this just because some people weren’t paying attention. Roblox gave a pretty fair amount of warnings prior.


Hi NWSpacek - I’m sorry you might have to close your game for this reason. Please let us know if you are having problems with the migration.

Regarding the prior notice: We announced this numerous times over the last year or so, including these posts from last August and November. I strongly recommend reviewing them for important information you may have missed.


Are you guys aware of the fact that conveyors don’t properly work on PGS and moving bodies often phase through anchored parts in locations far from the (0,0,0) origin? I have a train game that has a 50000 stud long map. Toward the end of the map some parts sometimes start phasing through each other. This is a PGS issue, because the problem no longer persists once I turn it off.

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Can you please post a simple repro so we can investigate and fix this?


The first clip is how it is supposed to work without PGS

The second clip is what happens with PGS physics solver

In this clip, the vehicle doesn’t move when the conveyor is fired. Instead the character is launched if it leaves the vehicle

The collision of PGS physics solver is way too stiff, which often causes the vehicle to violently bounce around track and derail at high speeds. The success rate for a complete run without PGS is 90% and still 0% with PGS on even after 15-20 attempts.

The instability and bugs of PGS physics solver is game breaking and should not be forced on games until the system is improved. I’ll have to close down my game for the same reason as Steam Age; the conversion will likely require rebuilding the whole game. Even if I do rebuild the whole game, it is unlikely it will ever be as stable with the current PGS. I tried converting about 1-2 years ago, it has improved since then, but still needs a lot of work.


I’m afraid I will have to also permanently put on hold the revival of one of my old games (which relied heavily on the SpringSolver), as PGS handles BodyMovers differently, I would’ve liked to attach a repro file so you could see for yourself the issue here but I’m currently on mobile…
(I’ll edit the post once I get the repro file)

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Could you provide a simple repro level so we can investigate the sources of the problem.


This is about 2/10 of the game with the basic systems in place. This was built in 2014, so the workspace is pretty messy
Hyperloop.rbxl (2.5 MB)

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Steam Age is now completely updated to PGS. Conversion to PGS took much less time than expected, and we are publishing it later today.


How do you deal with the little magical bumps that derails the train and the stiff collision?

If anyone wants to learn a little about how the new PGS physics can work together, here’s a bike!

It uses two counter-weights to help balance and turn, as well as a single BodyGyro (which isn’t really needed but helps to dampen some swaying).

The counter-weights are connected via WeldConstraints, which allows you to move them about freely to change the balance and centre of gravity.
This REALLY effects how the bike turns, balances and lands, so mess around with it and see what you can make. =)

pgs bike.rbxl (21.5 KB)

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I suggest you look at this thread on the devforums: How do I make my minecart stay on the rails? It was asking the same question as yours: how to make a physics object work the way it’s supposed to, when it just can’t.
The short answer is to use a completely scripted, node-based approach and use AlignPosition and AlignOrientation objects to ignore the physics problem completely. The thread itself has a ton more information about how to implement this and what the alternatives can be.

Unfortunately in my game that is not an option

We added a block underneath the rails to keep the train from hopping off. The trains used to slide on the ballast, and be held in by the rails, so all the trailing points did not have both rails functional (the trains would slosh around a bit but ultimately would work fine). The trains now rest on the rails, so we had to modify all those switches to use both rails. We had more manpower than I expected, so while @Synchorus and I were maintaining the junctions, @dr01d3k4 and Synchorus were also upgrading all the trains to use the new wheels.

It was a brilliant display of teamwork to get a huge amount of work done in just a few days. Steam Age is now updated with PGS, and you can play it here:


Dude that’s awesome. Glad to hear you guys did it!

The main problem I have is actually not the instability of PGS, but instead the part misalignment and the inconsistent conveyors. Parts that are perfectly aligned in studio tend to misaligned in game, causing bumps in my perfectly aligned tracks and ultimately derailment. This is not a PGS issue, its been around since 2016. It wasn’t a problem for my game until now, because the legacy physics engine used to absorb the bumps. Meanwhile, the stiff collisions of PGS made it far worse. I guess the fact that vehicles are traveling at 500 sps+ in my game amplified the issue. How did you get around this? Or is this never an issue for your game?