Pocket MMU Pre-Prototype

Next Update

In progress...

1. Idler Door — 623ZZ Bearing (3 × 10 × 4 mm, BMG + bearing)

   This update will also require reprinting the 6-door camshaft. I'm already testing the corresponding angles, although the current camshaft is shortened for 4 doors. This helps me avoid juggling two different angle configurations at the same time.

   Stay tuned for the upcoming servo configuration and CFG angle updates

1. Electronic Cover

2. 6 doors

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Custom MMX Variant — Experimental

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This is a custom variant of the MMX, largely based on the original design, but with several modifications I made during assembly and testing.

The goal was to solve some of the issues I encountered, make assembly and maintenance easier, and make certain parts more tolerant of small variations in assembly and 3D printing.

To be honest, this version is still very much in kamikaze mode. It works and I’ve already tested it, but it has nowhere near the amount of testing that the original MMX has gone through. That’s why I decided to release it as-is, so others can try it, find issues I may have missed, and share their feedback or ideas.

I’m not presenting this as a definitive improvement or as a completely new design. It’s my own variant, based on the existing design and modified according to what I encountered during assembly.

For now, I consider it a functional Pre-Prototype. There will most likely be changes, fixes, and probably a few parts that I end up redesigning yet again.

If you decide to give it a try, any feedback, issues, or suggestions are more than welcome. I’m getting tired of this being just my problem... and my coffee mug’s. ☕

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What I Modified

The main modifications included in this variant are:

• New belt tensioning system, along with a new servo pulley and clip.

• Press-fit assembly in several areas, including the doors.

• Adjusted tolerances and clearances to make assembly easier and compensate for small variations in 3D printing.

• Modifications to the camshaft and the filament detection/retention system.

• Modifications to the ECAS fittings and the use of smaller M3 inserts.

• Easier magnet removal in case they are accidentally installed in the wrong position.

• Visual motor movement indicator.

• New mounting points for inserts and future modifications.

• New side maintenance and calibration cover, with additional internal clearance.

Overall, these changes are a mix of mechanical adjustments, assembly improvements, and small design changes aimed at making maintenance easier and leaving more room for future modifications.

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How Much of the Original MMX Can Be Reused?

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This variant was not redesigned from scratch. The original camshaft was essentially the starting point, and from there I modified the parts based on the issues I encountered during assembly and testing.

Luckily, most of the components from the original MMX are still compatible, so if you already have one assembled, you shouldn't need to replace almost everything. In general, you’ll only need to add a few screws, inserts, and some parts specific to this variant.

In the CAD, I separated the hardware into two components: MMX and New Screws. The original components are colored green, while the new ones keep their default color, making it easy to tell which parts can be reused.

The main differences are:

• 6802-2RS bearing: 15 × 24 × 5 mm, used as an alternative to allow the side cover to be removed.

• M3 inserts: M3 × 4 × 4.2 mm. I believe the original ones are slightly larger.

• Servo pulley and printed clip: I’m still waiting for the belt; for now, this is my Plan B.

• 4 × M3 × 5 mm screws for the door microswitches.

• 6 × M3 × 20 mm screws + 4 × M3 nuts for the cover and servo tensioner.

• ECAS 

Other than that, I was able to reuse practically all of the original hardware.

I recommend checking the New Screws component in the CAD before assembly to verify the required sizes and quantities.

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Press-Fit Door Assembly

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One of the main modifications was changing the door assembly so that the Part 1 + 2 ECAS + LED + Part 2 assembly can be installed almost entirely as a press fit, following a concept similar to the one used by Swandhis. The LED solder joint itself also helps keep the whole assembly securely in place.

I also brought back some slots and holes from my old remix to make it possible to remove the magnets with a tool in case they are accidentally installed in the wrong position or with the wrong polarity.

I also made a few adjustments in this area:

• More clearance for the BMG grub screw, preventing interference.

• More hexagonal shapes in some areas to make printing easier.

• Slightly taller spacers to prevent the doors from getting stuck.

• More precise microswitch positioning, making them essentially a matter of placing them in position and securing them with screws.

Microswitch note: I’m currently using some generic red microswitches, whose click makes it much easier to tell when they have been activated. If you use the original switches from the kit, you may need to add a small piece of paper as a shim, since they are slightly different. I’m working on a version specifically designed for the original switches.

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Visual Motor Indicator

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This is simply an aesthetic detail that indicates when the motor is running, and honestly, I really like how it turned out. It was an idea that came to me randomly while I was on the road.

It can be removed, but you would normally have to take the entire gear assembly apart, piece by piece. However, there is a slot on the top that allows it to be removed, and there is actually enough clearance to remove the entire assembly with the cover still installed.

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New Tensioning System

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I added internal guide channels for the tensioner mounts, both for the new tensioner part and the main motor mount. Once secured with screws and nuts, they stay in position, and the tension can be adjusted by moving only the corresponding part.

For tension adjustment, I recommend using a single screw to find the correct position first, and then installing the second screw to lock it in place. Trying to adjust both screws at the same time is rather impractical.

I also added the option to use a 6802-2RS bearing (15 × 24 × 5 mm), which allows you to test the MMU without having the side cover installed.

The cover retains the original bearing seat, so you can also use the original system without purchasing the 15 × 24 × 5 mm bearing.

New-You will need a GT2 belt, 196 mm long and 6 mm wide, as the belt included in the original kit is too short for this tensioning system.

Alternatively, you can use the clip linked below and adjust the tension to achieve a setup similar to the one I'm using in my prototype.

https://www.printables.com/model/305939-gt2-belt-clamp

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Camshaft and Alignment

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This is one of those small details that can look perfect in CAD but behave slightly differently in the real world.

During assembly, I noticed a small alignment difference that I’m not completely sure where it comes from, so I decided to give the system a little more room for adjustment to prevent small variations from affecting its operation.

One of the modifications was to extend the toothed section of the camshaft, allowing a little more GT2 belt adjustment range while keeping the same angles.

I also slightly increased the clearance, especially between the door and the camshaft when pressure is applied, with an approximate difference of +0.60 mm.

The idea isn’t simply to “make it loose,” but rather to achieve a more consistent fit, with enough pressure for everything to work properly without unnecessarily stressing the MMX base.

It’s a bit like leveling a print bed with a sheet of paper: you want enough contact and pressure, but you don’t want to crush everything by forcing it.

This small amount of extra clearance also helps prevent false positives during filament detection or retention.

To make testing easier, I’ll include both the original camshaft and the modified version, so you can directly compare what was changed.

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New Base Inserts and Extra Mounting Points

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I also added new mounting points for inserts in the base, leaving the structure prepared for future modifications and accessories.

The idea is to eventually use these points for things such as:

• Bases or mounts for securing the MMX to the printer.

• Additional brackets or supports.

• A mounting base for the buffer + hub.

• Any other modification or accessory that might come up later.

The goal is to have these mounting points already built into the base, so I don’t have to modify the entire base again every time I want to add something new.

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Side Cover — Maintenance & Calibration Cover

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I don’t consider this part to be simply a side cover. The main idea is to use it as a maintenance and calibration cover, allowing you to check the internal operation of the MMX without having to constantly take it apart.

I also increased the internal clearances quite a bit, especially around the belts. One of the things I liked the least about the original design was that some areas were a little too tight, so in this version I preferred to leave more room to see and check what is actually happening inside.

The cover is mainly designed to make the following easier:

• Visibility of the mechanism.

• Access for adjustments.

• Maintenance and calibration.

• Preventing possible interference with the belts and other components.

In short, I’d rather have a little more space and be able to see what’s going on than discover that a belt is rubbing against something after everything is already assembled.