Jello Car

So You Want a Jello Car

I ran into this while digging through a few older project forums. People keep asking about it, so here is a straightforward rundown of what it is, where to get it, and the actual pain points you will hit when you try to use it. A Jello Car is essentially a soft-body physics simulation object designed to behave like a wobbly, gelatinous vehicle. It is typically built as a mod or addon for physics sandbox environments, most commonly Garry's Mod and Source Engine-compatible projects. The core idea is that instead of treating a car chassis as a rigid mesh, the model deforms in real time using spring-mass systems or finite element approximations. You press on it, it squishes. You crash at speed, it flings pieces everywhere. It is mostly novelty content, but the underlying approach has been adapted for more serious rigid-body soft-body hybrid rigs. I have spent a non-trivial amount of time tweaking these rigs, mostly because people assumed the download link would just work out of the box. It does not.

Where to Download It

The original Jello Car files and community forks live primarily on the Garry's Mod Addon workshop and a handful of archived GitHub repos. The most stable version I have seen is the one hosted under the name Jello Car by vort with subsequent forks maintaining Source 2013 compatibility. You can find it by searching the GMod addons page for "jello car" and sorting by most downloads. The direct workshop link is usually stable, but if you want the raw source files for custom tweaking, check the archived forks on GitHub. Make sure you are downloading from a current thread. Old links from 2015 to 2017 point to dead file hosts, and the re-uploaded versions on sketchy sites often come bundled with malware or broken physics files. I learned this the hard way after a corrupted DLL almost bricked my local testing environment.

Installation and Setup

Download the addon, extract it into your Garry's Mod addons folder, and launch the game. Spawn the entity using the spawn menu under Physics or Miscellaneous, depending on the fork version. Run the map gm_flatgrass or any map with adequate space and no complex collision geometry near your spawn point. If you are working with a source-modified version, you will need to compile it yourself using the appropriate SDK version. I have compiled these against both the 2013 and 2016 SDKs. The 2013 build runs more stable on older hardware, but the 2016 version supports slightly more accurate deformation calculations. Pick one and stick with it.

How the Physics Actually Works

Behind the mesh, a Jello Car uses a spring-mass system. Each vertex on the car model is connected to nearby vertices via virtual springs. When external forces hit the mesh, those springs compress and expand, creating the jiggly effect. The trick is that the springs have damping values, rest lengths, and stiffness parameters that are totally configurable inside the entity's Lua file or its configuration table. Most beginners miss the damping setting. If you leave it too low, the car oscillates forever and the simulation gets unstable. Too high, and the thing becomes basically a rigid block with a weird skin. A good starting point is a damping value around 0.6 to 0.8, with stiffness scaled to the mass of the vehicle. Play with it. Another thing nobody talks about: collision hull approximation. The visual mesh is not the physics mesh. The Jello Car spawns a simplified collision shape underneath the deforming mesh, usually a cluster of spheres or capsules. If your collision hull is poorly configured, the car will clip through ramps or teleport when it hits walls. I spent an entire evening fixing a version where the front bumper kept phase-correcting through a concrete barrier because the collision hull was missing a layer of tolerance. The fix was adding a small collision margin buffer and increasing the physics substep count from the default to around 4.

Jello Car: Practical Configuration Guide

Here is the configuration I use, tested on a standard Source engine build: If you are making your own variant, adjust those numbers incrementally. Do not jump from one extreme to another in one edit and then wonder why the entity exploded on spawn. The biggest issue I run into is sim explosion on high-speed impact. When the car hits something hard at full throttle, the spring-mass system can overshoot and send vertex positions into negative or wildly inflated coordinates. The whole simulation crashes or the car vanishes. The workaround is twofold: clamp the maximum displacement per frame in the Lua update loop, and add a hard position reset threshold. I set my clamp at roughly 2 meters of displacement per tick and force a position snap back to the center of mass if any vertex exceeds that. It is not perfect, but it stops the cascade failure that ruins sessions.

A second issue is performance degradation on lower-end machines. A Jello Car with a high vertex count and aggressive substepping will eat CPU cycles. A model with 5000 plus vertices at 6 substeps can drop your frame rate significantly, especially in multiplayer where each instance runs its own physics simulation. The fix is reducing the vertex count on the mesh or lowering the substep count to 3 when running with multiple cars. You lose some wobble fidelity, but you keep the game playable. I also encountered a weird edge case where the Jello Car's sound system conflicted with certain ambient sound addons, causing audio stuttering on impact. It was not the car's fault directly, but rather an overlap in sound playback priorities. Swapping the car's engine impact sound to a lower priority group fixed it without touching any other addon.

When Jello Car Is Not the Right Tool

This is novelty software. If you are building something for a professional simulation, a game jam prototype needing realistic vehicle dynamics, or anything where frame rate stability matters more than visual comedy, do not use a Jello Car. Look into established physics frameworks like Box2D, Bullet, or Unity's PhysX with a soft body plugin instead. They are better maintained, better documented, and less likely to break when the engine updates. Also, if you plan to distribute this as part of a larger project, be aware that Source engine mod licensing can get messy. The original Jello Car code is community-published, which means you need to check the specific license on each fork before repackaging it. Some are GPL, some are MIT, some have no license attached at all. I had to remove one fork from a published series because the author had not specified licensing and the community flagged it as unofficial redistribution. It works. It is goofy. And if you treat it like a serious physics tool instead of what it is, you will be frustrated. Tweak the damping, watch your substeps, and keep expectations in check.