Animatronic Slime Project Update #3 - February Progress and Reflection

Welcome back. This time we have some attempts at casting the slime puppet shells, a reflection on the project thus far, and where I will be going from here.

Slime Puppet Shell Progress

Unfortunately, for reasons to be explained further in the section, I did not make nearly as much progress in February as I had hoped. Difficulties in casting the puppet dome meant I did not accomplish any of the goals set out in my previous post. As a reminder, at the end of January I had a new slime dome mold design which would allow for separating the mold without pinching the part. As I went to print, however, I discovered that I was out of filament. While waiting for the new filament to arrive (after having made a note to print future molds with a lower infill percentage), I was able to test different methods of post processing the molds.

Slime Mold Post Processing

As mentioned in my previous post, I planned to use both sandpaper and plastic cement to smooth the print lines in the molds in order to lessen their visibility in the cast silicone. Using my previous mold prototypes, I decided to compare the effectiveness of just sanding on its own versus sanding the part then finishing with plastic cement. For both, I used a sandpaper sequence of 120-220-400 grit.

Post Processing Technique Comparison: Sanding and Plastic Cement (Left) vs Sanding Only (Right)

Comparing the two, I found that while the plastic cement did produce a smoother surface where applied, it's adhesive qualities made it difficult to apply evenly, instead leaving an uneven surface of relatively smooth and rough patches. For this reason, I decided that the uniformly smooth result of sanding alone was better.

Puppet Casting - First Attempt

Once the new mold was printed and post processed, I tested pouring all three molds: the dome mold, the flat bottom mold, and the tube bottom mold for the breathing slimes. For this test I also tested dyeing the silicone for the first time, which was more difficult than expected. It was difficult to add the pigment to the silicone in a small enough dose, resulting in a more saturated final color more akin to blood or ketchup than a red slime.

Initial Slime Puppet Test Casting

This initial test revealed many flaws in my dome mold design. The small hole at the top of the mold resulted in the silicone entering the mold very slowly and pooling on the flat top. This necessitated repeatedly combing the silicone back over the hole to prevent it from running down the sides.

The second flaw was revealed when attempting to release the dome from the mold. A combination of the silicone's adhesion to mold and the mold's alignment pegs resulted in it being very difficult to separate. As I attempted to pry it apart, I found that the dome was splitting along the seam. Clearly another dome mold design was necessary.

The slime dome ripped as I attempted to remove it from the mold.

I saw more success in de-molding the slime bottoms, with the flat bottom being removed with no hitch at all, save a small amount of overflow from being overfilled. With the tube bottom mold, however, I found that the poured silicone and silicone tubing had issues adhering to one another. I have a couple ideas on how I could address this, namely scuffing the outside of the silicone tubing with sandpaper to give more surface area for the poured silicone to adhere to, and pouring more silicone over the two parts once the bottom sets.

The flat bottom after being de-molded. The shiny surface makes fingerprints visible under harsh lighting.

The tube bottom after being de-molded. I found that the silicone tubing and poured silicone did not adhere to each other.

Slime Dome Mold Redesign

Returning to the drawing board for the Slime Dome mold, I sought to address two major issues in the redesign: difficulty pouring the silicone into the mold, and improving separability. To address the first, I widened the hole at the top of the mold to increase the flow rate. Additionally, I added a shallow funnel shape around the hole to guide the silicone into the mold. To address the separation issue, I removed the alignment pegs entirely. Instead the mold used external alignment guides which could be removed after the silicone sets to separate the mold. Removing the alignment pegs also allowed me to make the mold a cylinder, rather than a rectangular prism, which would be more comfortable to hold. Finally, I purchased silicone mold release spray to treat the mold before pouring.

CAD of the redesigned Silme Dome Mold.

Puppet Casting - Second Attempt

With this second test I sought to address issues with the slime dome mold and silicone color. With a more conservative dose of pigment, I was able to get a far less saturated color, achieving a more "liquid", less matte appearance. Pouring the silicone for the slime dome was also much easier, however I noticed that as I poured the silicone in, the top of the mold lifted away from the bottom. I weighted the mold to prevent this.

Slime Mold V2 Test Pour. The Slime Dome Mold was weighted to prevent it from lifting up with the silicone.

Unfortunately, when it came time to de-mold the slime dome, I saw similar complications to the previous attempts. Despite the mold release applied, the two parts of the mold would not separate. This was perhaps due to the pressure applied by weighting the mold, though the smoothness of the cylinder likely didn't help as it was difficult to get a good grip on the mold.

Moving Forward - Reflecting on Current Progress and Future Goals

To cut to the chase: I will no longer be adhering to the project timeline I published at the start of the project. This was a difficult decision to make, but ultimately I felt it was the correct choice to prevent burning out on this project. Developing the slime molds has already taken far longer than I anticipated when I first wrote the project timeline, and the failures with the slime domes this past month have been discouraging, placing far more stress on me than I hoped this project would. Making this change will also give me more time to pursue multiple creative projects at once, rather than feeling I am neglecting one to support the other. I still plan to make regular progress on this project, alongside these update posts, but I am going to take my time to not burn out and make sure I design these puppets right before making the rather large investment in the show controller.

Speaking of the puppet design, I plan to begin this month by investigating another fabrication technique for the slime domes called slush casting. Slush casting is a process by which a mold is filled then left to partially set to a desired outer thickness before pouring out the rest. I plan to first test an additive version of slush casting, where I incrementally introduce small amounts of silicone to the mold, let it set, then repeat until it reaches the desired thickness, in order to reduce the amount of wasted silicone. I anticipate this may not work as the uncured silicone may settle to the bottom of the mold before setting. This method would additionally complicate dyeing the silicone, as the pigment should only be .001%-3% of the total weight of the silicone solution. These factors may push me toward accepting the waste associated with traditional slush casting. Once I am able to fabricate a proper slime dome, I will test adhering it with the flat slime bottom.