Power and brownouts

Read this page whenever a peripheral disappears rather than misbehaves. A device that vanishes mid-session — a camera, the speaker, an arm — is usually being starved of current, not failing.

The symptom pattern

You're looking at a brownout if:

• A USB device works, then disconnects mid-session, often under load.
• The robot logs show a device re-enumerating (… device has been disconnected, then a new device appearing).
• It's reproducible under load (loud audio playback, all cameras streaming, arms moving) and fine when idle.

Software bugs don't usually correlate with load like that. Power does.

The Pi 5's 600 mA aggregate USB cap

This is the big one. A Raspberry Pi 5 limits total USB current across all ports to 600 mA unless it is explicitly told the supply can deliver more. On a robot with cameras, arms, and a speaker, 600 mA is not enough, and peripherals brown out under load.

Robot Pis must set:

usb_max_current_enable=1

🚧 To write

• Where exactly this goes and how to verify it took effect.
• Which robot builds ship with it already set, and how to tell.

Confirming it rather than guessing

On the Pi:

vcgencmd get_throttled

🚧 To write

Decode the bits — which indicate undervoltage now vs. undervoltage since boot vs. thermal throttling — and show what a healthy reading looks like. Right now this is the fastest way to confirm a power problem and it's undocumented for operators.

Audio clips brown out the speaker

A near-full-scale audio clip drives the speaker amp and the hardware-AEC reference far harder than call speech. On a full-speed USB DSP speakerphone that's enough to brown the device out into a mid-stream USB re-enumeration.

The robot already clamps playback gain (NORI_SPEAKER_GAIN, default 0.7) to defend against this. If you're still hitting it: attenuate further client-side, add a powered USB hub, and use a more robust speaker.

Devices that come back wrong

When a USB device browns out and re-enumerates, it comes back as a new card number. Anything configured by number (hw:0) now points at nothing — permanently, until a restart.

Configure by name. For the speaker: NORI_SPEAKER must be a dmix alias (nori_out) or hw:CARD=<name>, never hw:<number>.

Motor torque and the power station

Motor torque is deliberately limited so a peak draw doesn't trip the power station. If you're seeing the whole robot cut out under aggressive motion rather than a single peripheral dropping, that's a different problem from a USB brownout — it's the supply rail.

🚧 To write

• The supported power configurations and their limits.
• What tripping the power station looks like vs. a USB brownout, so operators can tell them apart.
• Recovery procedure after a trip.

Setup: Power and cabling.