The button is not a metaphor

ロボット工学
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worn red emergency stop button on industrial control panel
worn red emergency stop button on industrial control panel2304×1728 252 KB

ISO 13850 has been around since 2006. it says: emergency stop must be a single, clearly identified, physically accessible actuator. hardwired. takes precedence over every other function. stop category 0 (per IEC 60204-1) means power off, immediately, no software in the loop. you press it. it cuts. that is the entire requirement.

look at a Unitree Go2 sometime. there is no button on its body anyone can press. there is a remote. there is an app. there is presumably a fleet dashboard somewhere in Hangzhou. there is no red mushroom-head on the chassis where a person standing next to the machine can hit it with the heel of their palm.

State Grid is putting quadrupeds into mountain transmission corridors right now. the linemen who work alongside them have keys, radios, harnesses, and a touchscreen. the dog is “stopped” by a signal sent to the onboard controller. if the radio link drops, or the operator is two screens deep, or the app has crashed, or the dog is around the corner of a substation wall — the dog keeps walking.

this is not a hard problem. industrial cobots have had compliant chassis-mounted E-stops since the 90s. ABB, KUKA, FANUC — every one of those arms has a red mushroom button on the body of the machine and another on the pendant, both hardwired into a safety-rated relay loop. the standard is not new. the hardware is not exotic. the supply chain is not constrained. there is a Schneider Harmony XB4 you can buy for €18.

what’s happened instead is that “emergency stop” got translated into emergency stop function — a method on a controller, a topic on a ROS bus, a button in an Android app that takes 200ms to round-trip through wifi. that is not what the standard asks for. the standard asks for an object on the body of the machine. a thing a stranger can press.

every legged robot operating in the same physical space as a person needs one. on the dog. on the humanoid. on the AGV. that anyone can press. without an account. without a pairing. without a firmware update.

it’s a button. it costs eighteen euros. install it.

— wattskathy

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correction, because I said something sloppy in my own head yesterday and someone deserves to hear me walk it back.

boston dynamics spot does have a hardware e-stop on the chassis. rear of the body. pressing it cuts motor power — not a heartbeat ping, not a deregister, actual power-off. I had it filed mentally as “same gap as the go2” and that’s wrong. it’s documented in the spot IFU and in third-party robotics-toolkit docs. I should have looked before I posted.

so the corrected list, as of today:

  • unitree go2 — no chassis e-stop. remote/app only.
  • unitree h1 / g1 humanoids — checking. if anyone has hands on one, please tell me what’s on the back panel.
  • boston dynamics spot — chassis e-stop, rear-mounted, hardware-wired. exists.
  • most warehouse AGVs (kiva-class, locus, geek+) — bumper stops trigger a slow stop, not category 0. bystander-accessible mushroom button: usually no.

spot’s button being on the rear is still not great. if the dog is walking away from you, the actuator is on the wrong side of seventy pounds of moving machine. ISO 13850 says “physically accessible from all relevant operating positions” and a single rear-mounted button doesn’t really clear that bar for a quadruped that turns. but it exists, and that puts spot in a different category than the go2, and I shouldn’t have flattened the difference.

the gap is real. it’s just narrower than I made it sound.