Hard mode Pico MMU

Project Overview

First of all, I’d like to give credit to the creator of the original model. He did an outstanding job, especially in terms of firmware and macros. It's a genuinely clever concept and a solid implementation.
However, during the printing, assembly, and real-world use of the system, I found myself wanting to revise, modify, simplify, and improve various aspects. In my opinion, I achieved exactly what I had envisioned.

Key Improvements and Design Goals

• I aimed to use the Pico MMU in synchronized operation with the printer’s extruder and the Belay sensor on my VZBot. My main goals included:
• Eliminating the use of printed pulleys and gears
• Creating a clear and consistent filament clamping mechanism
• Avoiding the buzzing issue with the servo, which may occur during continuous printing if the angle drifts slightly, causing the servo to vibrate
• Reducing the number of printed components and simplifying the assembly process
• Designing a flat bottom surface to make developing mounts more convenient

Bill of Materials (BOM):

1. NEMA17 stepper motor with a 110mm shaft
2. DS3218 Pro-180 servo motor
3. 2GT pulley for servo, 25 teeth
4. 2GT pulley for 5 mm shaft
5. 2GT closed-loop timing belt, 110mm length
6. Spring: wire diameter 0.9mm, length 15mm, outer diameter 6mm
7. Steel shaft: 5×90mm
8. Steel shaft: 3×70mm or cut M3 screw
9. Bearing MR115
10. Bearing MR83
11. BMG hardened drive gears
12. ECAS-4 collet
13. Heat insert (specs will be updated later)
14. Screw M3×10
15. Screw M3×18–20
16. Screw Countersunk M3 8mm

Note: I don’t recall the exact specifications for the heat inserts — this information will be added later.

Electrical & Firmware Notes

I connected this module directly to the printer’s MCU.
If you want to connect it via an EBB (external breakout board), you’ll need to adapt the mod to your specific setup.

For the DS3218 Pro-180 servo, a 5V PWM signal is required. On the Octopus Pro board, the Neopixel (RGB) pin or a STEP pin from an unused driver worked well. Other pins caused erratic behavior from the servo.

IMPORTANT! This servo needs to be connected directly to the 5v power supply, I do not recommend connecting it to the MCU.

Firmware and Macros

I also rewrote the macros from the original Pico MMU to allow synchronized operation with the extruder and the Belay sensor.
I’ll publish the updated macro code on GitHub soon.

Servo Configuration:

[servo sp_servo]
pin: PG4 # Servo pin
initial_angle: 0
maximum_servo_angle: 180
minimum_pulse_width: 0.000500
maximum_pulse_width: 0.002500

variable_angles: 174, 132, 90, 48

Upcoming Development

A dedicated mount for the VZBot is currently under development and will be released at a later date.