Positioner Build Guide

Bill of Materials

Qty	Component	Notes
1	ESP32 DevKit	Any variant with enough GPIO
2	TMC2209 stepper driver	UART mode, StallGuard support
2	NEMA 17 stepper motor	0.9° or 1.8° step angle
1	24V power supply	3A+ for motors
1	5V regulator or USB	For ESP32
-	Wire, connectors	See wiring diagram

Tip

The TMC2209 must be in UART mode, not standalone mode. This enables StallGuard sensorless homing and runtime configuration.

Mechanical Assembly

The positioner needs two axes of rotation:

1. Theta axis (polar, 0-180°): Tilts the antenna from zenith to nadir
2. Phi axis (azimuth, 0-360°): Rotates the antenna around vertical axis

Design Considerations

• Cable routing: Ensure cables can handle full rotation without tangling
• Balance: Center of gravity should be on the rotation axes
• Rigidity: Minimize wobble for accurate measurements
• Range limits: Mechanical stops for homing reference

Mounting Options

Approach	Pros	Cons
3D printed	Custom fit, cheap	Strength limits
Aluminum extrusion	Strong, adjustable	Heavier, more complex
PVC pipe	Very cheap, easy	Less precise

Electronics Assembly

1. Mount TMC2209 drivers

   Install both drivers on a breakout board or custom PCB. Ensure proper heatsinking—these drivers can get hot under load.

2. Wire motor connections

   TMC2209 Pin	Motor Wire
   A1	Coil A+
   A2	Coil A-
   B1	Coil B+
   B2	Coil B-

   Caution

   Never disconnect motors while powered—the back-EMF can damage the driver.

3. Wire UART connections

   Both drivers share the same UART bus but have different addresses:

   • Theta driver: Address 0x00
   • Phi driver: Address 0x01

   See Wiring Diagram for full pinout.

4. Power connections

   • 24V to driver VMOT pins (motor power)
   • 5V/3.3V to driver VIO pins (logic power)
   • ESP32 powered via USB or separate 5V regulator

5. Test before mounting

   Flash the firmware and verify both motors respond before final assembly.

Firmware Setup

See Firmware for build and flash instructions.

Calibration

After assembly:

1. Home both axes: Run positioner_home(axis="both")
2. Verify range: Move to extremes and check for binding
3. Tune StallGuard: Adjust STALL_VALUE in config.h if homing is unreliable
4. Set motion parameters: Use positioner_config() to tune speed/accel

Troubleshooting

Motor doesn’t move

• Check power supply voltage (should be 24V)
• Verify UART communication (TX/RX wiring)
• Check TMC2209 address configuration

Homing fails (doesn’t detect stall)

• Increase motor current in config.h
• Decrease homing speed
• Adjust STALL_VALUE threshold

Motors get hot

• Reduce motor current (if torque allows)
• Add heatsinks to TMC2209
• Reduce holding current when idle

Position drift

• Check mechanical coupling (loose setscrews)
• Verify microstepping is consistent
• Check for missed steps (reduce speed/accel)