Overhead Rotor

An alt/az pointer that physically slews to whatever the dashboard is tracking.

The Companion Rotor is a two-axis pointer that aims at the ISS, a satellite, or a planet — live. It's a dumb pointer: the Overhead dashboard broadcasts az/el over ESP-NOW, and the rotor homes itself, calibrates without any gear-ratio math, and tracks. Runs on a plain ESP32 devkit driving 28BYJ-48 or NEMA 17 motors — one firmware, with the motor type, pins, and switches all set in a browser after flashing.

Assembled 3D-printed pan/tilt head with a 28BYJ stepper and printed reduction gears — A printable base for this: hollerer's 360° pan / 180° tilt head (thing:314027) — 28BYJ-48 steppers, printed gear reduction, a microswitch per axis. Photo © hollerer, CC BY-NC-SA.

Assembled remix build in olive PLA with a controller enclosure — …or BalooRM's tilt/pan remix (thing:5461912) — the same dual-28BYJ mechanism, shown fully assembled. Photo © BalooRM, CC BY.

Flash it from your browser

One firmware for both motor types. Plug the ESP32 in over USB, click Install, and choose its serial port. Flashing takes ~1 minute and erases the device.

Your browser can't do Web Serial — use desktop Chrome or Edge. Serial access was blocked — allow it and retry.

After flashing, the rotor hosts a Rotor-setup Wi-Fi network — join it and open http://192.168.4.1/ to choose your motor type (28BYJ or NEMA 17), set pins, switches, and the ESP-NOW channel, and run calibration. Changing hardware never needs a re-flash. (NEMA 17 needs its own 12–24 V motor PSU.)

Board
Any plain ESP32 WROOM devkit. Drives 28BYJ-48 (ULN2003) or NEMA 17 (A4988/TMC2209).

Browser
Desktop Chrome or Edge (Web Serial). Won't work on Firefox/Safari/mobile.

Sensors
MPU6050 (el reference), an azimuth limit switch, optionally an elevation switch.

Requires a Chromium browser (Chrome / Edge) served over HTTPS or localhost. Web Serial does not work from a file:// page or over plain HTTP.

Wiring

These are the factory-default pins — change any of them in the Rotor-setup web UI (no re-flash). Optional switches stay off until you assign a pin there. Every switch wires to GND and reads active-LOW (INPUT_PULLUP).

Signal	28BYJ-48 default (ULN2003)	NEMA 17 (A4988/TMC2209)
Az motor	IN1–4 → GPIO 32, 33, 25, 26	STEP 26, DIR 25, EN 33
El motor	IN1–4 → GPIO 27, 14, 12, 13	STEP 17, DIR 16, EN 4
Az home switch required · az zero + auto-cal	GPIO 34 ↔ GND — GPIO34 has no internal pull-up, so add an external ~10k to 3V3.
El home switch optional	Any free GPIO, assigned in the web UI. If left unset, el homes off the accelerometer instead.
Travel end-stops optional · safety	Az CW/CCW & el min/max, assigned in the web UI. The axis won't drive past an active stop.
IMU — MPU6050	SDA 21, SCL 22, VCC 3V3, GND (I²C addr `0x68`).

Use a 6-DOF MPU6050 — not a 9-DOF. Only the accelerometer (the gravity vector) is read, to reference and trim elevation. A 9-DOF's magnetometer is never used — azimuth heading comes from the home switch + step count + your one-time SETNORTH — and sitting inches from the stepper coils a compass would read garbage anyway.

Then calibrate — no gear-ratio math

Use the buttons in the Rotor-setup web UI (or a serial monitor at 115200). Results persist to NVS and survive a reflash. Typical first run: CAL EL → CAL AZ → jog to north → SETNORTH.

Command	What it does
`CAL EL`	Measures el steps/deg against gravity (the accelerometer) — automatic, exact.
`CAL AZ`	Homes to the limit switch, jogs one full turn back to it → az steps/deg. Falls back to a guided `MARK` cal if cable-wrap blocks a full turn.
`SETNORTH`	Jog the pointer to true north first, then this stores the north offset.
`AZ± / EL±`	Jog an axis by degrees (used for `SETNORTH` and the manual az fallback).
`SHOW` / `HOME` / `RESET`	Print calibration · re-home · clear NVS back to `config.h` defaults.

Full build/wiring guide: rotor/README.md.

← Back to the Overhead dashboard flasher — the display this rotor points along with.

A great mechanical base for this: hollerer's 360° pan / 180° tilt head (thing:314027) — two 28BYJ-48 + ULN2003 with a microswitch per axis. In the web UI, home az to the pan switch and el off the accelerometer (its tilt switch sits at a travel extreme, not the horizon), and set a little az backlash comp for the printed gears.

Prefer an antenna rotator? The firmware is motor-agnostic (28BYJ or NEMA, chosen in the web UI), so it also suits other stepper az/el builds — e.g. jbyrns's AZEL Satellite Antenna Rotator for a ham Arrow antenna.

Source, hardware guide & backlog: github.com/JamesDavid/Overhead · Free for personal/non-commercial use (PolyForm Noncommercial 1.0.0). · DE KE7AQA