Rot32

Rot32 is an extremely low-cost (<150USD) ESP32-based antenna rotator which is suitable for amateur radio operators or hobbyists. It utilizes commonly available hardware and is easy to assemble, wire, and program.

Features

• 3D printable enclosure and gearing. Enclosure fits within 256x256mm bed
• LSM303 Accelerometer/Magnetometer automatically determines the current heading and elevation
• Worm gear motor drive locks position without power applied
• Wide antenna mast can steer multiple antennas at once while staying
• Rotctld protocol emulation over Wi-Fi allows all hamlib compatible applications to interface with the rotator
• Web interface for manual steering and changing motion and calibration parameters on the fly.

Build

Bill Of Materials

• 1kg Spool 3D Printing Filament (Preferably PETG, ABS/ASA)
• 4x R16-2RS Ball Bearings (2in OD, 1in ID, 1/2in Thickness)
• About 5ft 0.75in aluminum tubing
• 2x JGY-370 12V 6rpm DC Worm Gear Motor
• 6x M3 Plastite Screws
• M3/M4 Nut/Screw Assortment
• ESP32-S3 Dev Board
• L298N H-Bridge Motor Driver

Wiring

Defaults from config.py for ESP32-S3

Signal	Pin
I2C SDA	GPIO8
I2C SCL	GPIO9
AZ+ / AZ- (PWM)	GPIO4 / GPIO5
EL+ / EL- (PWM)	GPIO6 / GPIO7

Firmware Install

1. Flash MicroPython from micropython.org/download for your module.
2. Edit config.py: set WIFI_SSID, WIFI_PASSWORD, and the pin numbers.
3. Copy the project files to the device, e.g. mpremote cp *.py *.html :.
4. Reset the board. The IP address is recorded in the log, readable at http://<device-ip>/api/log or over serial with SERIAL_LOGGING_ENABLED.

Usage

Web UI

Browse to http://<device-ip>/ for a simple control interface:

• Position: live azimuth/elevation readout, plus the current target while a move is in progress.
• Manual control: press-and-hold direction buttons plus a speed slider.
• Go To Position: numeric azimuth/elevation entry, plus Park and Reset.
• Motion Tuning: arrival window, arrival speed, slow-down distance, and acceleration.
• Calibration: declination, offsets, invert flags, axis selection, smoothing, and a magnetometer calibration wizard.

First-time setup

1. Pick the azimuth forward axis: rotate the antenna while level and try each of X/Y/Z until the Azimuth readout tracks correctly. Then tilt to a nonzero elevation and rotate again to confirm it is still accurate.
2. Pick the elevation axis pair: choose whichever of XY/XZ/YZ changes as you tilt the sensor.
3. Run the magnetometer calibration wizard: click Start, sweep the sensor through a full 360 degrees for 30 to 60 seconds, then click Finish.
4. Set magnetic declination for your location, then trim the azimuth and elevation offsets.
5. Raise Smoothing if the readout is jittery. Keep it at 0% while tuning axes and offsets so the display reacts immediately.

If azimuth is accurate at one heading but drifts at others, that is magnetic distortion near the sensor. Use the wizard, not the offset field, which shifts every heading by the same amount.

rotctld

TCP server on port 4533, accepting short and long command forms.

Command	Long form
P Az El	\set_pos
p	\get_pos
M Dir Speed	\move
S	\stop
K	\park
R 1	\reset
_	\get_info
1	\dump_caps
dump_state

Direction values for M: 2 up, 4 down, 8 left, 16 right. Locator commands are recognised but return unsupported.

printf 'p\n'         | nc 192.168.1.50 4533
printf 'P 180 30\n'  | nc 192.168.1.50 4533
printf 'M 16 60\n'   | nc 192.168.1.50 4533
printf 'S\n'         | nc 192.168.1.50 4533

The extended response protocol is supported by prefixing a command with +:

printf '+\\get_pos\n' | nc 192.168.1.50 4533

Future Improvements

• Enclosure design should be tested to failure and revised accordingly. There is room for improvement in the screw standoff design which mates the two halves.
• Better waterproofing could be achieved through gasketing material around the edges and using shaft seals or some other 3D printed rubber to prevent water ingress at the bearings.
• Spur gear design can be revised to reduce backlash. A belt-drive was tested but tensioning became complicated and required more space.
• Gear-to-pipe connections should use a circumferential clamping force rather than a set screw. Aluminum is soft and a screw pressing directly into the pipe works itself loose over time.
• Encoders can be implemented for better precision. JGY worm gear motors are available with built-in encoders.
• LSM303 motion algorithm can be improved. Magnetometer calibration is quite good for static precision but polling rate and filtering could use some work.