PolyexponentialScheduler_motorway_edition

When you pick "polyexponential" in a KSampler's scheduler dropdown, this is the node you're actually describing. A scheduler's job is to decide how much noise is removed at each step - it turns the step count into a list of sigmas, the noise levels the sampler walks down. The polyexponential family does that with a curve you can shape, and rho is the shape knob.

At rho = 1 the schedule collapses to a plain exponential curve. Raise rho and the steps bunch up toward the low-noise end, giving you more refinement time near the end of denoising and less stomping around in the early chaos. That's why polyexponential with a modest rho is a staple in custom-sampling chains - it's a cheap way to spend your steps where detail actually forms.

On the bus

This _motorway_edition is the stock PolyexponentialScheduler rewired for the MOTORWAY 🚌💨 bus. It has no data inputs to speak of - everything is widgets - so the MOTORWAY input is optional and the node can even start a bus itself.

The widgets are the whole story:

• steps (default 20) - how many sigmas to generate.
• sigma_max / sigma_min (defaults 14.614642 / 0.0291675) - the noise range. The defaults are the standard modelizer range; you usually leave these alone unless you're matching a specific sampler's expected span.
• rho (default 1) - the curve shape. 1 is exponential; 2–7 is where the "more steps at low noise" behavior lives.
• OUTPUT_SIGMAS_key (default SIGMAS) - where the generated sigmas are parked on the bus.

The only return is the bus. Downstream, whatever sampler reads the sigmas needs to look under SIGMAS. In a bus workflow that's typically SamplerCustomAdvanced_motorway_edition, whose INPUT_sigmas_key defaults to sigmas - so you'll either rename your output key to sigmas or change the sampler's key. Case matters.

Install

Pure Python, zero dependencies, no models to fetch:

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

Or via ComfyUI Manager under the pack title ComfyUI_agilly1989_motorway, then restart.

Watch out for

Two pack-specific caveats. First, beta project: the README's own warning is "IF THINGS BREAK ITS BECAUSE I BROKE IT," and the _motorway_edition clones were auto-generated by a cloner that build 1.1.7 disabled. A fresh install may not include this node at all - if it's missing from your menu, it's not you. The stock PolyexponentialScheduler does the identical job without the bus.

Second, the standard bus failure: KeyError: 'hash_...' doesn't exist in motorway means a key was never stored upstream. For a scheduler that's almost always the sigmas key not making it onto the bus because your sampler is reading a different name. Check both sides of the key.

And the timeless scheduler advice still applies: if you're on a guidance-distilled model that expects a specific schedule, don't hand-roll sigmas unless you know what the model wants. The stock Karras or model options exist for a reason.