Calibration

Calibrate servo positions for precise cloth folding

Complete calibration process walkthrough for precise panel positioning

Why Calibrate? Each servo has slightly different mechanical tolerances. Calibration ensures all panels move to exact positions for consistent folding.

Set Home Position

Step 1: Power On and Connect

  1. 1.Connect power supply to the robot
  2. 2.Connect Pico 2W to computer via USB
  3. 3.Open serial connection (mpremote, Thonny, or screen)
  4. 4.Press Ctrl+D to soft reboot
# Connect to REPL
mpremote

# You should see:
=== Fabrica Cloth Folding Robot ===
Initializing I2C...
PCA9685 found at 0x40
Servos initialized
Ready for commands
>>>

Step 2: Move All Servos to Home (90°)

The home position is defined as all panels lying flat (90° servo angle).

# In the REPL, run:
import servo_controller
sc = servo_controller.ServoController()

# Move all servos to 90 degrees (home position)
sc.home_all()

# Wait for servos to reach position
import time
time.sleep(1)

Step 3: Attach Servo Horns

With servos at 90°, attach the servo horns to panels:

  1. a)Place servo horn on servo shaft in the flat position
  2. b)Align horn so panel will be horizontal when at home
  3. c)Press horn firmly onto splined shaft
  4. d)Secure with included servo horn screw
  5. e)Repeat for all 4-8 servos

⚠️ Critical: Servo horns must be attached while servos are at exactly 90°. If misaligned, panels won't fold correctly.

Calibrate Movement Range

Understanding Servo Angles

Standard servo motors rotate approximately 180°. For Fabrica:

0° Position

Panel fully up

90° Position

Panel horizontal (home)

180° Position

Panel fully down

Test Movement Range

Test each servo individually to find safe operating range:

# Test Panel 1 (servo 0)
# Start at home
sc.move_servo(0, 90)
time.sleep(1)

# Test upward range
sc.move_servo(0, 45)   # Halfway up
time.sleep(1)
sc.move_servo(0, 0)    # Fully up
time.sleep(1)

# Return to home
sc.move_servo(0, 90)
time.sleep(1)

# Test downward range
sc.move_servo(0, 135)  # Halfway down
time.sleep(1)
sc.move_servo(0, 180)  # Fully down
time.sleep(1)

# Return to home
sc.move_servo(0, 90)

Watch for mechanical limits:

  • • Stop if you hear servo straining
  • • Check for collisions with adjacent panels
  • • Verify hinges are not binding
  • • Note the actual usable range (may be less than 0-180°)

Record Calibration Values

Document the safe range for each servo in the config file:

# Edit config.py on the Pico
SERVO_LIMITS = {
    0: {"min": 10, "max": 170, "home": 90},   # Panel 1
    1: {"min": 15, "max": 165, "home": 90},   # Panel 2
    2: {"min": 10, "max": 175, "home": 90},   # Panel 3
    3: {"min": 20, "max": 160, "home": 90},   # Panel 4
    # Add more servos as needed
}

# These limits will prevent damage from over-rotation

Fine-Tuning

Adjust Speed and Acceleration

Control how fast panels move:

# In config.py, adjust these values:

# Movement speed (degrees per second)
SERVO_SPEED = 100  # 100° per second (moderate)
# Try: 50 (slow), 100 (moderate), 200 (fast)

# Acceleration ramp
USE_ACCELERATION = True  # Smooth start/stop
ACCEL_TIME = 0.3  # Seconds to reach full speed

# Simultaneous movement
PARALLEL_PANELS = True  # Move multiple panels at once
# False = sequential (one at a time)

PWM Frequency Tuning (Advanced)

Most servos work at 50Hz, but some prefer different frequencies:

# In config.py:
PWM_FREQUENCY = 50  # Standard: 50Hz

# If servos jitter or buzz:
# Try: 60Hz (some digital servos prefer this)
# Try: 333Hz (analog servos, smoother)

# Pulse width range (microseconds)
PULSE_MIN = 500   # Typically 500-1000
PULSE_MAX = 2500  # Typically 2000-2500

# Adjust if servos don't reach full range

Test Coordinated Movement

Test moving multiple panels simultaneously:

# Move panels 1 and 2 together
sc.move_multiple([
    (0, 45),   # Panel 1 to 45°
    (1, 135)   # Panel 2 to 135°
])
time.sleep(2)

# Return to home
sc.home_all()

# Test all panels in sequence
for i in range(4):  # For 4-panel build
    sc.move_servo(i, 45)
    time.sleep(0.5)
    sc.move_servo(i, 135)
    time.sleep(0.5)
    sc.move_servo(i, 90)
    time.sleep(0.3)

Calibration Verification

Run Calibration Test Sequence

This built-in test verifies calibration:

# Run calibration test
import sequence_manager
sm = sequence_manager.SequenceManager()
sm.run_calibration_test()

# This will:
# 1. Move each panel through full range
# 2. Check for smooth movement
# 3. Verify home position accuracy
# 4. Test coordinated movements
# 5. Report any issues

Expected Results:

✓ All panels move smoothly without jerking

✓ No mechanical binding or collisions

✓ Servos return to exact home position

✓ No unusual sounds or vibrations

Save Calibration

Once satisfied with calibration, save settings:

# Save current configuration
sc.save_calibration()
# Settings saved to: /calibration.json

Calibration Troubleshooting

❌ Servo Jitters at Home Position

  • • Insufficient power supply current → Use 5A power supply
  • • Mechanical friction → Lubricate hinges, check for binding
  • • Wrong PWM frequency → Try 60Hz or 333Hz

❌ Panel Doesn't Return to Same Position

  • • Servo horn loose → Tighten horn screw
  • • Servo gear backlash → Use higher quality servos
  • • Software timing issue → Increase delay between moves

❌ Limited Range of Motion

  • • Adjust PULSE_MIN and PULSE_MAX values
  • • Check mechanical stops (hinges, frame)
  • • Verify servo is not damaged

Calibration Complete! ✨

Your robot is now calibrated and ready to learn folding sequences. Let's teach it how to fold your first garment!

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Assembly: Testing & Calibration
Operation: Folding Sequences
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