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I am planning to build a CoreXY machine with a tool changing system. I am using Marlin firmware and BigTreeTech SKR PRO as the controller board. There are 3 options in Marlin for tool changing systems:

  • Switching tool head
  • Magnetic switching tool head
  • Electromagnetic switching tool head

I want to use the switching tool head in my project using a servo/stepper motor. So I have 2 questions:

  1. Should I use a servo or stepper motor? Which one does the board and firmware support?
  2. Where should I connect the servo/stepper on the SKR PRO and what should the value of SWITCHING_TOOLHEAD_SERVO_NR be?

Note: I am also using a BLTouch leveling sensor So I can't connect the servo to the BLTouch servo port.

Edit: After so much research, finally, I found the way to do this. For the first question, Servo is the best choice. First, we need to configure tool change x and y position and servo rotation angle in configuration.h file and leave SWITCHING_TOOLHEAD_SERVO_NR as it is. Also, uncomment #define NUM_SERVOS and set it to 2.Then we need to open Marlin\src\pins\stm32f4\pins_BTT_SKR_PRO_common.h file and in the Servos section, add the following line:

#define SERVO1_PIN                          PC9

In the end, connect the servo signal pin to the PC9 pin on extension 1 and the VCC and GND pin to the pins next to the PC9 pin that are GND and 5V.

Note: I haven't tested this because I don't have this board. If this way doesn't work, please tell me in comments.

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  • $\begingroup$ To my knowledge a single PWM pin in exposed on extension port 1, but recalling Arduino tinkering you can use any digital or analog pin for a servo. For a stepper you require more pins to control the movement, how many tools are you focussing on? Each tool requires a feeder stepper... E3D uses Duet boards, they have many options for additional steppers (either through extension boards). $\endgroup$
    – 0scar
    Sep 1, 2020 at 7:53
  • $\begingroup$ @0scar SKR PRO has 3 extruder outputs and because I use 2 of them, 1 of them (e2) will be unused. Also, my preference is to use a servo motor. But I don't know how to connect it to the board and configure marlin for it (pins.h, configuration.h,configuration_adv.h) $\endgroup$ Sep 1, 2020 at 8:40

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  1. Use a servo. This way you can use the digital pins to control it; or in your specific case PWM_PC9
  2. Connect it to the expansion port and configure one of the digital pins in the marlin configuration file. A servo will go to the minimum position when the pin goes low, and the max position when the pin goes high. I take it you don't need any stops in between since you're doing a tool changer.

If you figure out how to modify the code to support tool changing, I'd be interested to know as well.

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  • $\begingroup$ Thanks for your answer. Can you please tell me what SWITCHING_TOOLHEAD_SERVO_NR is and how can I use it, if you know? $\endgroup$ Sep 1, 2020 at 7:46
  • $\begingroup$ PWM_PC9 (pin 4 on extension 1) seems to be the only pwm pin available for use. I believe SERVR_NR is the index of the servo for the M280 command. I don't know enough about this part of marlin to be of much use. $\endgroup$
    – user77232
    Sep 1, 2020 at 13:40
  • $\begingroup$ After so much research, finally, I found the way to do this. For the first question, Servo is the best choice. $\endgroup$ Sep 2, 2020 at 16:36
  • $\begingroup$ First, we need to configure tool change x and y position and servo rotation angle in configuration.h file and leave SWITCHING_TOOLHEAD_SERVO_NR as it is. Also, uncomment #define NUM_SERVOS and set it to 2.Then we need to open Marlin\src\pins\stm32f4\pins_BTT_SKR_PRO_common.h file and in the Servos section, add the following line: #define SERVO1_PIN PC9 In the end, connect the servo signal pin to the PC9 pin on extension 1 and the VCC and GND pin to the pins next to the PC9 pin that are GND and 5V. $\endgroup$ Sep 2, 2020 at 16:36
  • $\begingroup$ I haven't tested this because I don't have this board. If this way doesn't work, please tell me. $\endgroup$ Sep 2, 2020 at 16:40

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