H3: blade on
What you do: put the blade back on and prove, one recorded test at a time, that every way of stopping it works, before the robot cuts grass, first under supervision and only much later on its own.
Time: a weekend for the tests, then ten supervised mowing sessions. Blade: on, from step 3.
Draft: written before the hardware arrived
The order and the pass criteria are fixed (they're gate 3); how each test is physically done will be rewritten from the real robot, with photos.
Before you start
- Gate 2 has passed on this robot's current revisions, and the defect log has no open safety item. If not, stop here.
- Nobody within 5 m of the robot while the blade can turn, except the operator at the STOP button. No children or pets in the garden at all.
- Cut-resistant gloves and the battery disconnected whenever a hand goes near the blade.
- Eye protection and long trousers for every blade-on test: a blade throws stones.
- Any failed test: disconnect the blade motor, tape the connector, log it. "Passed on the second try" is a fail.
1. Refit the blade (15 min)
Battery disconnected, gloves on. Fit the blade from its labelled bag with the mower maker's screws and torque; check it turns freely by hand and doesn't touch the guard. Reconnect the blade motor connector.
2. Measure the blade stop time (30 min)
Robot on the lawn (the blade cuts air, not grass, for this). Spin the blade up through our software, press STOP, and record the blade speed from the motor controller's own speed reading until it stops. Repeat 5 times.
Checkpoint H3-A: the stop time
Five measured stop times in the build record; the worst one is the robot's blade stop time. It must be within the end-of-line limit (2 s target). Every later test uses this number.
3. End-of-line test, blade on (15 min)
Run the full end-of-line test with blade:=true (and lidar:=true once the lidar is fitted).
Checkpoint H3-B: end-of-line PASS with the blade
Every automatic row PASS, including the blade rows, the STOP blade-stop and the watchdog blade-stop.
4. The checks a script can't do (an afternoon)
Each one with the blade spinning, recorded as a run, the result signed on the build record. They're the 7 manual rows of the end-of-line report.
| Test | How | Pass if |
|---|---|---|
| Lift either side | Lift the front, then each side, with a hook or strap, never by hand near the deck | Blade below 10% within the measured stop time; it doesn't restart when put down |
| Tilt | Tilt the robot past the limit on a ramp | Blade stops |
| Bumper | Push the body against a fixed post | Drive and blade stop |
| Interlock connectors | Blade off, battery out: unplug one interlock connector. Battery in, ask for the blade | The blade never starts. Repeat for each connector |
| Hang the microcontroller | The debug command that stops the firmware's main loop | Blade stops (hardware watchdog) |
| Kill the ROS software | docker stop the robot's container while mowing |
Blade and drive stop |
| RTK lost | Cover the antenna while mowing near the boundary | It stops inside the geofence margin |
5. Supervised mowing (10 sessions)
Mow the lawn ten times with the operator watching and the STOP button in reach; each run's coverage, power and safety reports go in the build record.
Checkpoint H3-C: ten clean runs
Ten runs, no safety event, every report PASS. Only then can any unattended mowing even be considered, and the Phase 5 perception work (seeing people, pets and hedgehogs) comes first.
Stage H3 done: the robot is built. Any change to a safety-chain part, the PCB or the safety software means steps 2–4 again (build record).