SamplerDPMPP_2S_Ancestral_motorway_edition

Some samplers settle into an answer and then stop changing. SamplerDPMPP_2S_Ancestral is not one of them. This motorway-edition clone of ComfyUI's built-in SamplerDPMPP_2S_Ancestral is an ancestral sampler: it injects fresh random noise at every step, so it never fully converges. Bump the step count and you don't refine the image - you get a slightly different one. That's not a bug, it's the personality.

For people who came up on SD 1.5, 2S ancestral was part of the classic "DPM++ 2S a Karras" combo that dominated that era. It's the sampler you reach for when you want a bit of variety and texture without fighting the deterministic sameness of pure 2M. Same seed, same steps? Reproducible. Same seed, different steps? Different result - which is exactly the trap beginners hit when they're told to "just raise the steps" to fix an image.

What it does on the Motorway

This is one of the *_motorway_edition clones from the ComfyUI_agilly1989_motorway pack. The pack's core idea is a named-key data bus - the Motorway - where you stash values under typed key names and read them back later instead of dragging wires around. MotorwayStart creates the bus, Motorway AxB ramp nodes store and fetch keys, and every *_motorway_edition node is a generated clone of a built-in ComfyUI node re-plumbed to read its inputs from the bus by key and write its outputs back to the bus. It always returns the bus so the chain keeps flowing.

It's a sampler factory, not a drawing node. Feed it a model and it hands back a SAMPLER object for SamplerCustom's sampler port. The only widgets you'll actually touch:

• eta (default 1.0) - scales the extra noise this ancestral sampler stirs in each step. Lower it for tamer output.
• s_noise (default 1.0) - the strength of that per-step stochastic noise. This is the knob that controls how "ancestral" it actually behaves; crank it and you're deep in chaos territory, drop it toward 0 and you're basically on plain DPM++.

The model arrives from the bus by key (the family convention, spelled INPUT_model_key defaulting to model on sibling nodes like the SDTurboScheduler edition), and the finished sampler is written back to the bus under your OUTPUT_SAMPLER_key - default SAMPLER, which is what a later SamplerCustom_motorway_edition will look for.

Installing it

It lives in the ComfyUI_agilly1989_motorway pack, no separate install. ComfyUI Manager: search ComfyUI_agilly1989_motorway, install, restart. Or:

cd ComfyUI/custom_nodes
git clone https://github.com/agilly1989/ComfyUI_agilly1989_motorway

No Python dependencies beyond ComfyUI itself, no model files to download.

The catch

Two things to know before you trust this in a workflow. First, the current release (1.1.7) has the clone nodes switched off: the two ClonedNodeMapping lines in custom_nodes/ComfyUI_agilly1989_motorway/__init__.py are commented out by a "HOTFIX - REMOVED MONKEYPATCH" commit. If the node isn't in your menu, uncomment those lines and restart. Second, the README is cheerfully explicit that this is an in-development beta - "IF THINGS BREAK ITS BECAUSE I BROKE IT" - and the author only guarantees "most" of the cloned nodes work. It's a fun experiment from a solo dev (find @agilly1989 in the Comfy Org Discord), but treat it as tinkering material, not infrastructure.