Work started on getting the MMU2S unit installed onto my prusa i3 Mk2.5s. It was a pain in the rear if I'm being completely honest, but I believe it will be needed to construct my fursuit head with multiple materials at once the way its designed. In addition to this I have made some good strides on the design in Fusion360, but not as far as I would like to be due to the amount of time with the MMU. I have expanded the scope of the electronics to include an inner glove that has buttons to control the head's LEDs.

Fusion360 Design

I have a laundry list of things to add to the design in fusion 360, and at the top of the list was incorporating LED circuit parts along the right cheek and back of the ears. The other was mounting the 40mm fans inside as part of the eyes. Ive added a jaw hinge (I might change later), and also locations for a proper headband to be mounted. I have made something that also kind of looks like a nose. There are still a bunch of things to account for, but this is the current state.

The ears will be made of flexible black TPU filament, but these strips will be printed in clear/opaque embedded inside and fused to the black TPU. The holes in the ears are spots to glue the LED to shine light in backwards into the ears. If this is done right, the ears should remain flexible and only light up from behind.

The cheek will be done in a similar way, but it will be clear TPU and annealed PLA, which based on my research into material bonding "should" work. Even if the PLA re-sizes during annealing process, the TPU should be able to change its shape to match if there is enough forces involved.

The trick to making these look like actual circuits under the fur will be to keep the fur shorter over these locations. The plan is to eventually have the teeth work this way as well, but I have yet to finish them. I plan on getting the nose button mount finished before finishing the teeth.

The nose button will be mounted under the nose. The nose itself will be made of TPU in black (squishy?). That should allow it to be pressed in like a soft membrane and activate the button underneath.

I have mounted and added small vents inside the eyes that allow intake of external air from the eye sockets. The two noctua fans are pretty quiet, but I believe you will still hear them when they are so close to the ears. I plan on adding in some memory foam ear parts and routing them directly to the outside of the cheeks. You wont be able to hear mostly anything inside the head, but I'm not sure that that's necessarily a bad thing?

The jaw needs some work. I'm trying to keep as much of the design as simple as possible, and going deep into the jaw fixture might be too much of a rabbit hole. I will revisit this based on how well the foaming PLA annealing tests go.


To accomplish the design goals of the head frame; in particular embedding clear filament within standard filament, it became obvious I needed to cash in on the MMU2S unit I purchased and had not gotten around to installing last year.

For those unfamiliar, "Multi-Material Units" are upgrades that allow standard 3D printers to use multiple rolls of filament using a single hot end. The Prusa ecosystem has a supported MMU2S upgrade which allows five different spools to be selected at for printing at a time. Another notable MMU on the market is the Pallet 2 which works differently, but achieves the same goal and is compatible with most other printers and not just Prusa printers.

My Prusa Mk 2.5s is by far the more accurate and reliable printer I have out of the two I currently own. I have brought this up through multiple upgrades since purchasing it as a Mk 2. I always approach taking it offline for upgrades with extreme hesitation, as its my primary work horse. It used to be the case that if an upgrade did not go smoothly I wouldn't have a 3D printer to replace parts, and that always had made me nervous to say the least.

Even though this has been the majority of the time spent in the last week, I am going to abridge my issues and experience. I proceeded to install the upgrade after printing Prusament PETG Ultramarine Blue versions on the extruder body parts at a lower layer height than the parts included in the kit. After the upgrade I was having a hard time getting the IR sensor working properly.

The IR sensor is a levered design that should only trip when filament separates the bondtech gears at the extruder. Problem was that the sensor was all over the place and inconsistent even after the recommended adjustments. Thinking there was a spacing issue, I re-printed the lever assembly parts using the same PETG, as I neglected to print these with the others because they were in another parts set. After replacing everything but the IR idler lever (Its black and not transparent which is good in this case), I got it to show on sensor debug screen when filament was inserted and as zero when it was not.

I proceeded to learn the latest version of  Prusa's Slic3r 2 and how to set up a test print, which went super well until the printer tried using the filament tips that had been extracted from the extruder (not fresh cut tips). The printer would load the filament into the extruder, but then extract it out past the bondtech gears, where the IR sensor could not detect it and fail. After hours and hours of debugging and support from Prusa, I determined that I skipped a very important step in the MMU2S manual. At that point I could managed to somehow stop the printer from loading any tips at all.

The PTFE (aka "Teflon") tube used in the redesigned extruder actually has a smaller inner diameter than standard PTFE tubes used in bowden setups. Standard PTFE tubes have an inner diameter of 2mm, while this tube is 1.85mm. This restriction allows the tips formed at the end of filament when extracted to be much closer to the actual diameter of the filament 1.75mm. In my arrogance, I used some standard PTFE tube I had a spool of instead of wasting the pretty pre-cut ones they had in the kit.

After replacing the tube and having the hold the idler door for a second to trick the sensor and load the  filament down for extrusion, I was able to get consistent loads and stop it from retracting past the gears. I'm not sure exactly why, but I assume that the filament was not going into the extruder nearly as far as I thought it was and getting caught.

Having consistent results with PLA and getting good retractions, I decided I would dedicate the printer to making some single color Automatic Rewinding Spools to replace the pain in the butt filament buffer that comes with the unit. It was a good time to step back and move on to other parts of the project for the time being. I'm fairly sure that I have never printed PETG parts with that much quality in the past. I believe that the more restrictive PTFE tube / extruder design is responsible.

Bluetooth Button Glove

I was thinking about controlling the LEDs with my phone. Then I thought, damn it must be hard to use a cellphone with fursuit paws. And of course, yeah that's an issue. Going through the Bluetooth module documentation, I found you can link two together and have them talk automatically.

The plan will be to make a simple glove that has buttons on it so it can control the suit head's LEDs. It will need a small battery, changer circuit, arduino, and buttons.