Raspberry Pi 5

A Raspberry Pi 5 sits next to the robot. The FT232R (servo bus) and a webcam are connected to it, so the arm can be controlled and watched remotely.

Item	Value
SSH	ssh raspberrypi5 (Tailscale; on the home network also raspberrypi5.local)
System	Raspberry Pi 5, 16 GB, Debian 12 (bookworm), aarch64
FT232R	/dev/serial/by-id/usb-FTDI_FT232R_USB_UART_B00033ZX-if00-port0 (/dev/ttyUSB0)
Webcam	Logitech C505, /dev/video0
Repository	~/myCobot/mycobot-280-lab (working copy) and ~/git/mycobot-280-lab.git (hub)
Julia	1.11 with juliaup: ~/.juliaup/bin/julia (only login shells have it on PATH)
Kernel	kernel8.img, 4 KB memory pages (since 2026-10-04)
Tools	Python ~/venvs/mycobot, ~/bin/arduino-cli (ESP32 core 3.3.10), Node ~/.local/opt/node, Go ~/.local/opt/go, /usr/local/bin/git-lfs-transfer

Kernel: 4 KB pages

The Pi 5’s default kernel (kernel_2712.img) uses 16 KB memory pages. Some prebuilt programs assume 4 KB pages and crash: Pagefind, the docs search indexer, failed with “memory allocation of 16 bytes failed”. /boot/firmware/config.txt now selects the 4 KB-page kernel:

[all]
kernel=kernel8.img

The original file is /boot/firmware/config.txt.bak-20261004. To undo it, remove the line and reboot. Check with getconf PAGESIZE (4096 now).

Repository sync

The Pi has a bare hub repository. The laptop has it as remote pi, and the Pi’s working copy clones it. Nothing goes to GitHub this way.

laptop  ──push/pull──▶  raspberrypi5:git/mycobot-280-lab.git  ◀──push/pull──  Pi working copy

Use plain git push pi <branch> and git pull pi <branch> on the laptop, and plain git push and git pull in the Pi’s working copy. Git LFS files (meshes, images) go with them:

• From the laptop, git-lfs (3.0 or later) runs git-lfs-transfer on the Pi over SSH (the pure-SSH LFS protocol).
• On the Pi, LFS works without it, because the hub is a local path.

git-lfs-transfer is charmbracelet/git-lfs-transfer, built from commit 971c028 and installed in /usr/local/bin on 2026-10-06. It has no release binaries and no Debian package. To install it again:

# on the Pi: Go toolchain in ~/.local/opt/go (from go.dev, linux-arm64)
GOBIN=/tmp/lfsbin ~/.local/opt/go/bin/go install github.com/charmbracelet/git-lfs-transfer@971c0284dc33b1ed3f7ed9dde5d4fc0cee62db6b
sudo install -m 755 /tmp/lfsbin/git-lfs-transfer /usr/local/bin/

Until 2026-10-06 the script tools/sync-pi.sh copied the LFS files with rsync, because the hub had no LFS server.

FT232R latency timer

On Linux the ftdi_sio driver keeps the latency timer in sysfs. A udev rule sets it to 1 ms each time the adapter is connected:

/etc/udev/rules.d/99-ftdi-latency.rules
ACTION=="add", SUBSYSTEM=="usb-serial", DRIVER=="ftdi_sio", ATTR{latency_timer}="1"

MyCobot.set_latency_timer reads sysfs on Linux, and MyCobot.default_port() gives the correct port on macOS and Linux. The scripts use both.

Camera

tools/pi/camera.sh uses 1280×960 MJPEG at 30 fps from the Logitech C505. This is the full 4:3 field of view of the sensor; 1280×720 crops the top and bottom. Each time it starts the camera, it sets the image settings below. The camera forgets them when it loses power.

Image settings

With the default settings the picture is flat: the camera’s auto exposure makes the white wall mid-grey, and the black base is grey. The settings below stretch the tones. Auto exposure and auto white balance stay on, so the picture adapts when the light changes.

Control	Default	Set to	Why
power_line_frequency	60 Hz	50 Hz	No flicker from the mains lights
exposure_dynamic_framerate	0	0	Always 30 fps. With 1, the camera can lower the frame rate in dim light.
contrast	32	64	Black is black, white is white; more detail on the arm
brightness	128	144	Lifts the picture after the contrast stretch. It is an offset, not an exposure bias.
saturation	32	40	Natural colours (cables, boards)

Measured on 2026-10-06 in daylight. Each line is the last frame of 4 s of stream. Brightness (luma, 0–255) and detail on the arm (the variance of the Laplacian):

Settings	Darkest 1%	Median	Brightest 1%	Clipped	Detail on the arm
Defaults	18	130	155	0%	32
brightness 192 only	87	204	231	0%	36
contrast 64 only	2	156	211	0%	101
contrast 64, brightness 156	2	206	255	3.3%	123
Set: contrast 64, brightness 144, saturation 40	2	183	236	0%	116

Settings that do not help:

• gain: auto exposure sets it. A value that you write has no effect.
• backlight_compensation 1: the picture is flatter (darkest 1%: 40).
• sharpness 40: detail 127 instead of 116. This is in the spread between runs (121 and 116 for two runs that differ only in saturation), so it stays at the default 24.
• brightness alone: it lifts the black too (darkest 1%: 87). This is the “milky” look.

The camera gave 29.8 fps with every setting in daylight. Not measured yet: dim light (evening). A white arm in front of a white wall has little contrast at any setting: a darker background or light from the side would help more than camera settings.

Watch it in a browser: the lab service streams it at http://raspberrypi5:8280/camera.mjpg (Tailscale and allowed computers): a 640×480 preview at 30 fps, or the full 1280×960 at 30 fps with ?full=1. The Control page shows the preview. While the service streams, it owns the camera: other programs get “device busy”.

Or watch it from the laptop over SSH (no open port; needs ffplay from brew install ffmpeg, and the lab service must not be streaming):

ssh raspberrypi5 '~/myCobot/mycobot-280-lab/tools/pi/camera.sh stdout' | ffplay -loglevel error -fflags nobuffer -f mjpeg -i -

Take one picture on the Pi: tools/pi/camera.sh snapshot /tmp/arm.jpg. It asks the lab service first (/snapshot.jpg) and opens the camera itself only if the service does not answer.