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BuildInstructionsMicroServoMG90S.md

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Part list

  • WS-MG90S micro servo
  • 2 x ITR8307
  • Custom PCB
  • Flat cables
    • 2 leads wide
    • 3 x 3 leads wide
    • 4 leads wide
  • pin header 1x4
  • 3D printed parts
    • baseBox
    • baseBushing
    • encDisc
    • encDiscTurningMount

Build instructions

Prepare parts

  1. Order PCB using gerber, BOM and CPL files:

    • PcbDesignes/combined/manufacture/gerber.zip
    • PcbDesignes/combined/manufacture/jlcpcbPcbaBOM.csv
    • PcbDesignes/combined/manufacture/jlcpcbPcbaCPL.csv

  2. Burn bootloader to PCB. The following instructions are for burning the bootloader using a Raspberry Pi.

    (For burning the bootloader with a stlinkv2 on windows, see stlinkv2 on windows. Also see bootloader programmer for pogo-pin connector for PCB programmer)

    Power PCB via USB from pi and connect:

        Prog1:D (swdio) -> GPIO 25
    Prog1:C (swclk) -> GPIO 11
    Prog1:Reset     -> 3.3v

    (GPIO nr are for a Raspberry Pi 3 B)

    1. Install OpenOCD on the pi with this guide: https://learn.adafruit.com/programming-microcontrollers-using-openocd-on-raspberry-pi/compiling-openocd

      or using apt-get:

         sudo apt-get install openocd

    2. Download bootloader: https://github.com/adafruit/uf2-samdx1/releases/download/v3.13.0/bootloader-itsybitsy_m0-v3.13.0.bin

      or latest from: https://github.com/adafruit/uf2-samdx1/releases

    3. Put *.bin file in new folder on pi together with the file burnBootloaderWithOpenOCD.txt and rename the script file to openocd.cfg

    4. run:

         cd \\|Insert name of folder on pi with the script
   sudo openocd

  3. Print objects in PrusaSlicer project file CadFiles/MicroServoMG90S/prusaSlicer.3mf

    Print in black PLA:

    • baseBox.stl
    • baseBushings.stl

    Print in white PLA:

    • encDisc.stl
    • encDiscTurningMount.stl

Modify the servo

Modify the servo according to the Build Video

Build Video

Build steps in video:

  1. Disassemble the servo

  2. The encDisc part has to be completely smooth and free from defects. Getting the required resolution out of a normal FDM 3D printer is basically impossible. So to get a smooth encDisc part we first need to file it down while spinning it:

    1. Remove the gear from the motor and mount encDiscTurningMount on motor axis. Then mount encDisc on encDiscTurningMount

    2. Apply 3-5 volts to the motor and file down 3D printing seams and printing lines until the surface of encDisc is completely smooth

  3. Mount the smooth encDisc and gear on the motor axis

  4. Solder on a 3 lead wide flat cable to each of the two ITR8307 sensors. Make sure that the orientation of the sensors are mirrored

  5. Mount the sensors in baseBox so that the LED segment (pin 1) of the sensors are oriented towards each other

  6. Solder the ITR8307 sensors and potentiometer to the PCB

  7. Put baseBushing on the center axis of the gear box

  8. Insert motor into baseBox, solder motor connections to PCB and screw everything together

  9. Done

Configure

  1. Power servo (5 volt) via pin header and connect to computer via micro USB

  2. Run python3 ./ArduinoSketch/configurationWizard.py

  3. Create a new configuration file by clicking Create new, select defaultMG90S.h as template, and choose communication node nr

  4. Transfer the initial configuration to the servo by clicking Transfer to target

  5. Select Optical Encoder to calibrate encoder

    Calibration example:

    1. Move servo to 100 deg and Lock position by clicking Lock
    2. Set Motor pwm value to 320
    3. Set Start motor pwm value to 450
    4. Choose position resolution Fine (~4 min) or Ultra (~8 min)
    5. Click Start calibration

  6. Identify system parameters with Pwm and system identification

    Calibration example:

    1. Move servo to 100 deg and Lock position by clicking Lock
    2. Set Motor settle time to 0.1 s
    3. Set Min motor pwm value to 320
    4. Set Max motor pwm value to 1023
    5. Set System model cycle time to 0.6 ms
    6. Click Start calibration

  7. Calibrate motor position dependent disturbances with Motor cogging torque (optional)

    Calibration example:

    1. Click Set advanced parameters
    2. Set Control speed to 32
    3. Set Inertia margin to 2.0
    4. Click OK
    5. Set position resolution to Standard (~3 min)
    6. Move servo to 100 deg
    7. Click Start calibration

  8. Calibrate nonlinearities in output potentiometer with Output encoder calibration (optional)

    Calibration example:

    1. Click Set advanced parameters
    2. Set Control speed to 28
    3. Set Inertia margin to 1.8
    4. Click OK
    5. Set position resolution to Fine (~4 min)
    6. Move servo to 100 deg
    7. Click Start calibration

  9. To test the final configuration select Test control loop