Peter Shryock's Pyro-Toilet Progress journal, notes and Repo link

[Ashenstride]

Here is the link to my personal Repo regarding my contributions to the pyro-toilet project.

Public Invention Oklahoma Team contribution - Pyro Toilet

I will copy my progress journal entries below.

[Ashenstride]

Entry #1 [12/17/2025] SUMMARY

System moving forward (current concepts):
The pyro-toilet is progressing toward a sealed, plug-and-play, plumbing-free system in which bio-waste falls into an elastomeric bowl containing a conductive, clumping dry mix (currently magnetite-based or magnetite-integrated) that enables coating and rapid thermal response. Vertical vibration (“tossing”) combined with a ribbed bowl is intended to improve coating uniformity and mechanically break down clumps, after which a simple basket-style sieve-lift transport is favored for its robustness and low cost to separate clumps from loose mix and transfer controlled portions into a sealed, staged thermal chamber. A carousel or equivalent pre-load/seal mechanism is envisioned to maintain incinerator isolation and allow rapid follow-up use. The thermal process is two-stage: low-temperature dehydration followed by high-temperature pyrolysis to convert waste into biochar, with char retained for later removal and gases routed to downstream treatment.

Hazards and risk considerations:
Primary hazards include airborne dust and aerosols from dry-mix agitation (especially magnetite), requiring a fully sealed system, likely negative pressure zones, and filtration; mechanical abrasion and clogging risks that make bearings, rails, and fine tolerances inside the dirty zone undesirable; and gas-phase dangers from pyrolysis, including carbon monoxide and combustible syngas. The gas handling system must therefore incorporate flame arrestors to prevent flashback, CO monitoring, and either an afterburner or catalytic treatment before exhaust. Noise, heat leakage, and long cycle times observed in existing commercial incinerator toilets are also functional hazards from a usability standpoint and must be minimized.

Heating alternatives and complements to magnetite:
Magnetite remains attractive as a rapid induction susceptor for initial heat-up, but its ferromagnetic behavior drops off around ~585 °C, below desired final temperatures (~725 °C), so supplemental or alternative heating is required. Options include conductive carbon-based susceptors (graphite, carbonized biochar beds), metallic susceptors or liners (stainless steel, Inconel, or iron alloys designed for induction coupling), resistive electric heaters for post-ramp temperature escalation, or hybrid systems where induction rapidly dehydrates and preheats while resistive or radiant elements complete pyrolysis. Designing a custom conductive absorbent litter that incorporates carbonaceous or metallic phases could reduce airborne powder issues while extending effective induction heating beyond magnetite alone.

Additional key points to carry forward:
Benchmarking against existing systems (TinyJohn, Cinderella) highlights the importance of achieving significantly shorter, quieter cycles as a core differentiator. The system must be tolerant of large variability in waste size and composition, function without oxygen in the thermal chamber to ensure pyrolysis rather than open incineration, and remain modular and serviceable for real-world deployment in flood-prone or infrastructure-limited environments. Early emphasis on repository structure, documentation, and off-the-shelf component identification is essential to avoid premature custom part design and to keep the project scalable, auditable, and aligned with future Public Invention collaboration.

[Ashenstride]

Entry #2 [12/31/2025]

Today, Lawrence and I had a video-call via Discord to do joint research and discussion, furthering our progress on the pyro-toilet development.

We discussed obtaining unbranded pressure pots wholesale for more affordable prototyping. We plan on modifying the first pot to attempt pyrolysis and biochar production.

After further deliberation, we concluded that our current most ideal model for the pyro toilet will be a large chamber containing a smaller chamber (the pyrolysis zone) separated by rockwool (an insulator). The inner chamber will be mounted to the outer chamber by flexible mounts to allow the inner chamber to vibrate freely. We will use a voice coil in an attempt to create vertical vibrations to break apart the biochar shell around the biowaste product, exposing fresh biowaste to the air to accelerate the bio charring process. We discussed the inner chamber containing a flexible liner to preserve the inner chamber integrity, followed by a sort of rigid mesh screen or basket to sieve out the biochar ash from the conductive substrate, allowing the top surface (the target induction zone) to be free of the previous cycle's biochar. The vibrations and shaking during the pyrolysis cycle should help clean off the conductive/absorbent substrate, allowing for reuse each cycle (at least to some extensive degree).

Anything in the inner chamber will have to be rated for extreme temperatures so as not to melt, combust, or degrade. Anything fibrous like rockwool, or fiberglass, will have to be treated as fine particulates capable of becoming airborne particles. The material will need to be coated or sealed off to prevent any safety hazards.

We discussed USA, EU/UK/CAN laws and regulations for products of sanitization, combustion, pressurization, and toxic gas handling. We learned that if we can keep the target pressures within the system well below 15psi, we can avoid needing some strenuous certifications.

For commercialization, the system needs to be user-friendly, near impossible to install incorrectly, and safe for disassembly/maintenance when the system is off, cool, and depressurized. Moreover, we must consider fail-safes for the same properties and ask ourselves "if this component fails or gets obstructed, what will happen?" and solve those problems before they can happen.

Attached below are WORD documents detailing the next steps and considerations.

https://github.com/user-attachments/files/24398496/Next_Steps_Roadmap_Residential_Pyrolysis_Toilet_System.docx

https://github.com/user-attachments/files/24398497/Next_Steps_Mechanical_Design_and_Prototyping.docx

[Ashenstride]

Entry #3 [01/07/2026]

Today I am working in FreeCAD to create a simple concept design with general systems, parts and assemblies.
"Make it first, then make it good later."

I am conducting research into voice coil actuators as a method to generate tossing and stirring of the media to cover, and break down the biochar as it is produced. I am looking into off-the-shelf components first, to see if there is a viable solution currently accessible within a reasonable cost margin; otherwise, we'll need to design one for this application.

With a mixture load of (X) lbs we will need to have a vertical deceleration (Vda) >/= gravity from the bowl in order to create mixture displacement from the bottom of the bowl. The greater the difference between Vda and g, the greater the displacement and thus the greater the tossing/mixing of the media and the contents inside. The cap being, the distance from the top of the settled mix to the bottom of the upper-lid.

For a voice coil, using the formula:

     a_Max​=((2πf)^2)A 

     where a_Max = max vertical acceleration
     f = frequency in Hz
     A = displacement amplitude

We can manipulate the static/dynamic conditions of the mixture by modifying the a_Max to g ratios:

    0.3–0.8 g: reduces static friction, promotes creep and rearrangement
    0.8–1.2 g: “near-weightless” moments begin; bed loosens and circulates
    >1.2 g: frequent lift-off / ballistic hops (more aggressive, noisier)

Of course, this is a simplified and ideal scenario, as other forces will be involved that will resist the rate of change, such as friction; however, it is a nice starting point.

I had a discord video meeting with Lawrence to discuss the basic BOM needed for the full system, as well as what the two next steps action items are for us:

(1) Obtain a stovetop pressure pot and modify it by installing the induction coils and 1-way gas outlet w/ pressure regulator.
     The goal is to achieve biochar conversion. 

(2) Attempt to agitate conductive media and control agitation via voice coil (or same induction coil by using some tech
     wizardry).

We identified several material candidates for an in-system, high-temp, non-conductive mesh filter to separate conductive media from biochar:

Silica fabric (high-silica cloth):
              -    Non-conductive (electrical insulator)
              -    Continuous at 800°F is fine (silica fabrics are typically used well above that)
              -    Comes as woven cloth / tape / sleeves you can cut and sew into a bag
              -    You can choose weave tightness: tighter weave = smaller effective “holes” (but slower flow)

        Search terms: “high silica fabric cloth”, “silica filter cloth”, “silica fabric sleeve”

        Gotchas: silica cloth can shed fibers and can be abrasion-sensitive if ash is gritty and there’s a lot of rubbing/vibration. 
        If you’re shaking it hard, go heavier weight.


Ceramic fiber fabric (e.g., alumina / alumina-silica like Nextel-style cloth):
              -    Excellent continuous temperature margin (way beyond 800°F)
              -    Non-conductive
              -    Often stronger at temperature than standard silica/glass fabrics
              -    Available as cloth, braid, sleeves

       Search terms: “ceramic fiber fabric cloth”, “alumina fabric”, “Nextel ceramic fabric”

       Gotchas: usually expensive, and some ceramic fabrics are stiff/itchy to handle.


Fiberglass cloth (E-glass or S-glass):
              -    Non-conductive
              -    Many fiberglass textiles can survive around 800F, depending on resin/binder content and the exact glass type
              -    Easy to source in many weaves

       Search terms: “fiberglass cloth high temperature (no resin)”, “E-glass fabric 800F continuous”

       Gotchas: avoid anything sold as “fiberglass cloth” that’s actually resin-coated (that coating will cook off/smoke). 
       Also, long-term strength at temp varies by grade.

Learned how to create parametric designs in FreeCAD:

1. Change workbench to "spreadsheet"
2. Create new spreadsheet (2 columns with 4 rows icon in the toolbar)
3. rename to parametric (not necessary, but convenient for communicating to team members)
4. type data nomenclature in an arbitrary cell A.
5. type a dimension number in adjacent cell B (without units of measurement? Can/Will add later.)
6. select appropriate cell B and populate the alias zone with the appropriate nomenclature.
7. Right click cell >> properties >> display unit >> type in unit
8. Create geometry with ballpark dimensions.
9. constrain dimensions (highlight feature and press "D" on keyboard.
10. Click function icon to open expression editor.
11. type <<{spreadsheet name}>>.{alias} (e.g.... <>.width
12. Click OK.
13. If necessary, recompute file.

I vibe-coded a Macro to expedite the process. Execute macro to create a parametrics spreadsheet and assign cell values for prep, fill out the cells accordingly, then execute the macro again to apply the updates. BOOM.

Parametrics.zip

Updated the macro to allow and change the internal name of the "Parametrics" spreadsheet to "p" so when calling for the parametric value in an expression, instead of typing "Parametrics.{alias}", you can now type "p.{alias}" for faster input.

Parametrics_updated.zip

[Ashenstride]

Entry #4 [1/09/2026]

Today, I'm picking up where I left off last time. I spent a good bit of time learning about FreeCAD's parametric dimensioning system using internal spreadsheets and links. With that, I can mock up some general parts with rough dimensions that I can adjust later as needed by changing the dimensions in the local part spreadsheet file. In fact, I need to look at if there is a local BOM system in FreeCAD, otherwise, I may see if I can integrate a parts-list into my parametrics spreadsheet-making Macro.

We are having a meeting later today, so I want to have a few things prepared for that. I'll start by working on the pressure vessel CAD file, then address the remaining BOM items as they are sourced.

Brainstormed with Lawrence more. Sourced a good pressure cooker pot that's affordable and would make for a good proof-of-concept, and even a first prototype (with some modifications. Its a Hawkins pressure cooker, posted in the prototype parts considerations list. (https://www.amazon.com/HAWKIN-Classic-CL20-Improved-Aluminum-Pressure/dp/B00VNMLIZU/ref=pd_ci_mcx_mh_mcx_views_0_title?pd_rd_w=Bf9eB&content-id=amzn1.sym.679481c3-2bf4-4843-80c0-ffb319282e84%3Aamzn1.symc.c3d5766d-b606-46b8-ab07-1d9d1da0638a&pf_rd_p=679481c3-2bf4-4843-80c0-ffb319282e84&pf_rd_r=JDW06VMQNVQEMBMR231K&pd_rd_wg=8Pr7M&pd_rd_r=15fef810-e27d-4711-a88a-28910a213864&pd_rd_i=B00SX2YZMG&th=1)

I am considering the use of steel shot instead of magnetite/bentonite mixture. I believe the steel shot is more likely to make an excellent medium for rapid heating via conduction, as well as a good medium for cracking and disturbing the sample as a biochar shell forms, exposing fresh matter to the intense heat. Possibly a combination of large and small shot, or a mixture of all three. During our proof of concept, we can test different mediums and compare energy efficiency, proficiency, and speed of cycle.

I need to think of a convenient way to quickly cool down the environment and prevent over-heating of components (especially during back-to-back cycles). Liquid-cooled? Peltier boards? cooling/shunting fans?

Next-steps:

Lock down a BOM for the pyrolysis test.
Send order request to Rob by next meeting.