Playa Sprawler

Open-source personal mobility optimized for accessibility and maintainability. A camp chair on four identical, hot-swappable, self-powered wheel modules — packed into one piece of Burner Express luggage, rated to the rider's mass down to every tube, joint and cord, and repaired by a community fleet in under a minute.

Site: https://playasprawler.outright.io · structured after BoardingFlow.

The idea in five lines

1. Four identical wheel modules (motor + gearbox + brake + battery + Ethernet node in one brick) dock anywhere on the frame; the dock tells the module which corner it is.
2. Two identical control modules (left tread, right tread) — lever, pedal, joystick, sip-puff: any input form publishes the same message.
3. Ethernet only for signals (M12 D-coded, UDP multicast pub/sub, no master); a separate SELV power bus. Traction current never crosses a dock.
4. A rating code in the DNA: every load-path part is analysed, proof-tested and marked PS-100 / PS-125 / PS-150; the vehicle's rating is the weakest part, enforced on the label and in firmware.
5. One bag — 62 linear inches, 50 lb — on the Burner Express bus. This constraint designed the vehicle.

Repository

analysis/    ps_params.py (single source of truth) + truss, stability, energy, flotation, axle, packing → results/
cad/         CadQuery generator: joiners grown from the frame geometry, wheel-module carrier, assembly → exports/ (STEP, STL, SVG)
firmware/    PS-Bus reference simulator (deterministic + real UDP multicast) and message schemas
docs/        methodology, requirements, architecture, rating code, module specs, tests, fleet ops, regulatory, caveats, ADRs, sources
seat/        seat flat pattern (generated)
site/        the single-page site (src/ template + app.js → index.html via scripts/build_site.py)
scripts/     build_site.py, check_ratings.py (CI gate)
.github/     deploy.yml (main → S3 + CloudFront), pr.yml (analysis, CAD, simulator, site preview)

Run it

pip install -r requirements.txt
cd analysis && python run_all.py            # results/results.md + results.json for all rating classes
cd ../cad && python ps_cad.py               # exports/*.step, *.stl, view_*.svg
python ../firmware/sim/psbus_sim.py --check # scripted hot-swap scenario with assertions
python ../scripts/check_ratings.py          # the rating gate CI runs
python ../scripts/build_site.py             # site/index.html

Change a number in analysis/ps_params.py; everything downstream regenerates. Never edit a number in a doc or on the site by hand.

Headline numbers (PS-125, from analysis/results/results.md)

Bag	660 × 450 × 450 mm (61.4 in), 22.49 kg of 22.68 kg — margin 0.19 kg
Wheel module	16 × 3.0 tubeless on a mini geared hub motor, 7s1p 85.7 Wh, 4.35 kg, 135 mm wide
Frame	25 × 22 CF tube (0.74 kg), 10 printed joiners, 5 mm Dyneema cords, structural canvas seat
Worst safety factors, 2.5 g	tube 11.1 · cord 3.7 · seat edge 3.7 · axle 2.1 (assumed steel)
Stability	tip at 0.49 g lateral; limiter at 0.25 g; 2.0 m minimum radius at 8 km/h
Range	23 km hard playa · 8 km soft playa · 2.5 km dry loose sand
Fail-safe	wheel stops 200 ms after the last valid command, 300 ms ramp

Read this first

docs/13-caveats.md. There is no prototype yet; the mass margin is 0.8 %; the axle steel is assumed; the vehicle is only legal in Black Rock City as an Accessibility Vehicle for a rider with a documented need.

CI and deployment

Two workflows, mirroring the Outright Mental static-site pattern:

• pr.yml — on every pull request: analysis, rating gate, CAD export, simulator self-check, site build, and a site-preview artifact.
• deploy.yml — on push to main: the same build, then aws s3 sync to the playasprawler.outright.io bucket (immutable cache headers on assets/, must-revalidate on index.html) and a CloudFront invalidation.

One-time setup for the deploy target:

1. S3 bucket playasprawler.outright.io (private, served through CloudFront with an origin access control), default root object index.html.
2. CloudFront distribution with an ACM certificate for playasprawler.outright.io (us-east-1).
3. Route 53 / DNS: playasprawler.outright.io → the distribution.
4. Repository secrets: AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY (an IAM user limited to that bucket and cloudfront:CreateInvalidation on that distribution), AWS_CLOUDFRONT_DISTRIBUTION_ID.

License

Hardware CERN-OHL-S-2.0 · software Apache-2.0 · documentation CC-BY-SA-4.0. See LICENSE.md.