mikkeli
0af2c956e4
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz
61 lines
3.4 KiB
Markdown
61 lines
3.4 KiB
Markdown
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type: report
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date: 2026-10-15
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---
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# Z27AG CAN: second pass, against OBD-II and GNSS
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Sessions `000007-20261015T192938` and `000008-20261015T200202` (car Orin): doors, tailgate,
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bonnet and wipers (checklist step 10–11), then a short drive with GNSS (3D fix, helix antenna)
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and OBD-II through the ELM327 on the K-line, all on the Orin's clock. The first time CAN, OBD-II
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and GNSS were recorded together. About 30 minutes; 1190 OBD-II samples of each fast value.
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## Confirmed
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| Signal | Where | Evidence | Registered as |
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|---|---|---|---|
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| Engine speed | `210` bytes 4–5, BE, 1 rpm (pass 1) | equal to OBD-II `0C`: median ratio 1.0000, median difference 4 rpm, 1190 samples | `engine_rpm` (unchanged) |
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| Coolant temperature | `449` byte 2, −40 °C | equal to OBD-II `05` within ±1 °C (median 0.0) over 86–97 °C; no other byte tracks it | `coolant_temp_c` |
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| Vehicle speed | `231` bytes 6–7, **little-endian**, **0.0577 km/h per count** | steady cruising (> 15 km/h, GNSS change < 1 km/h over 2 s, 117 fixes): spread 2.6 % against GNSS | `vehicle_speed_kph` |
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| Four wheel speeds | `235` four words, **little-endian** (pass 1 left the byte order open) | big-endian misses by 28 km/h rms; little-endian fits. Words 0, 1: 0.0578; words 2, 3: 0.0581 km/h per count against GNSS | not yet: which word is which wheel waits for the jack-stands run (fronts turn, rears stay) |
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Scales are against **GNSS**, so they include this car's tyres today. **OBD-II speed reads 3 % low**
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against GNSS (0.9706): the ECU's figure is no better a reference than the ABS frames. The two
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word pairs of `235` differ by 0.5 %, the usual size of a front/rear tyre difference.
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## Doors, tailgate, bonnet, wipers
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| Thing | Bit | Notes |
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|---|---|---|
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| Driver's door | `423.0.4` | its own bit (pass 1); also sets any-door |
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| Passenger, rear left, rear right | only `423.2.1` (any door) | no bit of their own |
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| Tailgate | only `423.2.1` | with the driver's door open, `423.0.4` cleared on closing it while `423.2.1` stayed set until the tailgate shut |
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| Bonnet | nothing | a mechanical latch with no switch, as expected |
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| Front wiper running | `423.3.3` | set through "low" and "high"; nothing in a 4 s "interval" window. Medium confidence; also explains pass 1's unexplained `423.3.3` stretch |
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## IMU calibration, checked against GNSS
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Level from session `000006` (two still stretches, the ground's 1.9° slope cancelled), forward from
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`000008` (three stops, one launch; 3512 samples, mean spread 12.7°). The module sits upside down,
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about 24° off level, turned so its X axis points forward. Calibrated, the marked stretches read:
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| Stretch | IMU longitudinal (0.25 s mean, peak) | GNSS |
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|---|---|---|
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| Stop, 48 → 0 km/h | −0.35 g | −0.28 g |
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| Stop, 45 → 0 | −0.17 g | −0.17 g |
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| Stop, 40 → 0 | −0.21 g | −0.18 g |
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| Launch | +0.32 g | +0.36 g |
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Lateral stays at about 0 in all four: forward is straight ahead. GNSS reports about once a second,
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which smooths short peaks.
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## Not found
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- **Intake air temperature:** no byte of `449` tracks OBD-II `0F` (29–51 °C here).
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- `449` bytes 0, 1, 3 move like temperatures but match nothing on OBD-II.
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## Notes on the recording
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- **The Orin froze mid-drive** (19:59; hardware watchdog reset at 20:01:47), splitting the drive
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over two sessions. orin-nano-env-setup has the investigation.
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- OBD-II through the ELM gave each fast value about every 2 s (K-line, ~250 ms per request).
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