Godot / Jolt Physics and small objects (cm / mm)

Godot Version

4.2

TLDR

I i use Jolt, Will there be problems in simulating small objects (3-4cm), and (2-4mm)

Question

I am looking at building a small simulation of a mechanical process rig, that will use physics to simulate objects moving on a conveyer belt.

I have experiance in doing this in 3.x (I made : https://virtualplant.didacticservices.co.uk/)

My question is regarding small objects. Previously i didnt care about scale, as the simualtion was just a simulation, but here i am quite keen to get the scale right, as i will be working with imported CAD files.

The objects are “3-4cm cans” that will be filled with “2-3mm balls”

  • think mints in a mint tin for example

Will simulating at this scale cause problems?

Even the godot UI doesnt seem to cater for zooming in that small very well

Would i be better making everything 10x scale?

jolt docs

https://jrouwe.github.io/JoltPhysics/#conventions-and-limits

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Thanks, but i searched docs already, and there is nothing on that page that specifically addresses size - it talks about “5km distances” and “small objects”

Was wondering more if people had any actual experiance

All godot and blender measurements are in m, so it would seem to make sense to use accurate measurement

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Ahh - I see :

Note that the physics simulation works best if you use SI units (meters, radians, seconds, kg). In order for the simluation to be accurate, dynamic objects should be in the order [0.1, 10] meters long and have speeds in the order of [0, 500] m/s. Static object should be in the order [0.1, 2000] meter long. If you are using different units, consider scaling the objects before passing them on to the physics simulation.

So this would indicate 0.1m - 10cm to be the smallest size that makes sense?

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Hi @calumk , did you end up applying a factor of 10 or more to your project? What’s your experience been like?

I also have a project with many objects that have real-world dimensions on the order of 1cm, and some even on the order of 1mm. The physics, rendering, and general editor tweaks I’ve had to make due to the small scale have been compounding. I want to try scaling everything up by x10 or x100, and even though some scripting will take care of much of the work, implementing this change across the project will still be a day or two of quite tedious edits and validations due to the stage that the project is in.

So I thought I’d revive this thread before initiating that work, in case you had any advice from your experience.

Hey - In the end I did not progress with this project - It was a side project for me and i ran out of time.

It seems like it should be possible to adjust jolt/godot, rather than scale everything

Even if it meant having to recompile godot/jolt, - I guess the right person looking at the right bit of the stack would probably be able to figure this out fairly easily.

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