Engineering, anatomy
The kit, taken apart.
Belt, collar strip, and ankle bands, opened up so a stranger can rebuild them: every part with its position, the signal path stage by stage, and how it is worn. Every latency figure is modeled.
The exploded view
Ten parts, one wearable.
Pick a numbered part on the figure to read it, or read the full list under the drawing; both carry everything.
4. Waist belt
Where: around the waist, on skin or a thin base layer
Eight motor pods around the trunk: where it buzzes is where it would hit you.
Every part and where it sits, in text
- 1. Collar strip (around the neck, over a base layer): Four coin motors speaking head height: the doorframe, the branch, the sign.
- 2. Chest mount (center chest, on an elastic strap sharing the belt anchor): A quick release cradle for the wearer's own phone, the Brain, out of the warning path.
- 3. Sensor head (front of the belt): Two laser grids (forward and ground), the radar, two outward angled sonars, and the IMU.
- 4. Waist belt (around the waist, on skin or a thin base layer): Eight motor pods around the trunk: where it buzzes is where it would hit you.
- 5. Reflex controller (in the belt hub): The RP2350: fuses the sensors, applies the three laws, drives the motors. No operating system, its own watchdog.
- 6. Spine (belt hub, behind the isolation boundary): The ESP32-S3: logging and Bluetooth to the phone, fed one way by the Reflex, never able to write back.
- 7. Battery pack (center back on the belt): One protected 3.7 V pack over the spine of the body, inline fuse, keyed connector, never charged while worn.
- 8. Magnetic breakaways (between the bands): Snag a band and it disconnects instead of dragging you; a band detaches without tools.
- 9. Left ankle band (left ankle): Four coin motors for the ground: stairs up sweeps upward, stairs down warns down.
- 10. Right ankle band (right ankle): Four coin motors, mirror of the left, so the ground speaks to the leg that leads.
The signal path
Sensors to reflex to driver to skin.
One table row per stage, with the modeled time it spends there. The whole path is modeled at about 70 ms for the world ahead and about 120 ms at the ground, modeled; the motor's rise time is the first bench measurement.
| Stage | What happens | Ahead, modeled | Ground, modeled |
|---|---|---|---|
| Sensors | Two VL53L8CX laser grids, the RD-03D radar, two JSN-SR04T sonars, the BNO085 IMU expose and integrate a frame. | 16 to 25 ms | 33 to 66 ms |
| Readout | Frames travel to the Reflex over the sensor I2C bus and the radar UART. | 2 to 5 ms | 5 to 10 ms |
| Fusion and the three laws | The RP2350 fuses a per column nearest distance map, detects drop offs, and produces twenty amplitude and rhythm commands. | 2 to 5 ms | 3 to 6 ms |
| Drive and rise | DRV2605L drivers write the motors in closed loop; the LRA rises to a felt buzz. | 10 to 20 ms | 10 to 20 ms |
| Skin | The wearer perceives the buzz where the body would be hit. | 5 to 15 ms | 5 to 15 ms |
| Total, modeled | about 70 ms | about 120 ms | |
The six signals
What the kit says, and where.
Each signal has a place on the body and a preset in the simulator, so you can feel what the words mean.
- Obstacle leftat left belt zones.Feel it in the simulator
- Obstacle centerat center belt zones.Feel it in the simulator
- Obstacle rightat right belt zones.Feel it in the simulator
- Head heightat the collar strip.Feel it in the simulator
- Stairs upat the ankle bands, sweeping upward.Feel it in the simulator
- Stairs downat the ankle bands, warning down.Feel it in the simulator
Comfort
Worn for hours, or not worn at all.
The comfort facts from the record; where a number is missing, it says to be measured.
- Worn under clothing
- The belt and ankle bands sit on skin or over a thin base layer; the collar sits over a base layer. Attenuation through one thin fabric layer is budgeted and will be measured before any perceptual claim.
- Weight per band
- Under 200 grams per band is the pass line; total on body electronics and bands, excluding the phone, about 700 to 900 grams, and likely lower.
- Straps and closures
- Breathable elastic webbing, soft brushed skin side liner, hook and loop plus a cam buckle. Rounded skin side edges, compliant TPU pod faces, the battery center back so nothing pulls forward.
- Heat, sweat, chafe
- Nobody feels the weight; they feel heat, sweat, chafe, and strap migration, which is where the engineering effort goes. A rest after about two hours of continuous wear is the starting standard until measured on real wearers.
- Per wearer calibration
- Vibrotactile sensitivity varies and falls with age, so a per wearer amplitude calibration step is planned. To be measured.
The signal design itself is tested with blind wearers: we play a pattern, ask what it feels like, and keep the patterns people read correctly. That practice set the first generation's direction and it runs through the second.
A research note
Why the three laws are laws.
From the record's placement sources, docs/01 and docs/02.
The three laws map onto structured vibration research on location, intensity, and motion. Location: the record anchors the belt zones to abdomen localization work reporting about 92 percent correct identification with eight tactors around the torso, near perfect at the navel and spine. Intensity: the coin motors park their energy in the 200 to 300 Hz band the skin senses best, so closer can honestly mean stronger. Motion: the record allots four motors per readable stroke, so a moving thing can be followed as a sweep. The citations live in the record files, and nothing beyond them is claimed.