Overstimulated Tofu (Bio-Cube)

Overview

Just like us, every living bio organism gets overstimulated. We set out to create a bio material cube made out of Agar Agarthat senses human proximity through an IR distance sensor, responding with a servo-driven breathing mechanism that contracts as you approach — simulating a living organism reacting to the stress of an overstimulated environment.

Keywords: Biomaterials, 3D Modeling, Fabrication

Team Members: Brian Bishop with help from Yesuel Song, Matt Griffin, Alana and Audrey Oh (shop staff)

My role: Creating Biomaterial and 3D Modeling

Status: Completed, Github

Contents:

Mechanical Mechanism

BioMaterials

3D Modeling & Printing

Putting it All Together

View Final Media

Process

Mechanical Mechanism

Initially, our thoughts were to somehow have a moving mechanism within the box. I thought of this in several ways, with a motor inside and offset weights.

Feedback: There likely wouldn’t be enough force to move the box. Instead, perhaps try a solenoid or an active gyroscope.

An active gryoscope seems to involve too much weight and figuring out how to break the spinning wheel would be challenging. The vibrational motors keep coming back so two prototype ideas:

1.) Place four weights on the corners of the box. See if some combination of them moves the box even a little

2.) Explore a solenoid

Another piece of feedback was to default to traditional ways of doing motion instead of trying to recreate it. Instead focus efforts on enclosing an existing mechanism and hiding it.

Other potential tries:

3.) Explore existing mechanisms for rotation and linear movement and try to hide it under the box

4.) Figure out how to control a ball bearing with a sensor or motor → cover ball bearing

Pivot to moving walls (Linear Actuators)

Rack and pinon

Other potential Linear Actuators (Scissors)

Wedge

[ wall ] /\ [ wall ]

wedge

We decided to pursue the simple linear actuator mechanism and scissor mechanism. A more comprehensible visual of what we planned to try to the right. This proved to be less ideal because we would need a rigid body to keep the weight in place and thinking of enclosing all of this was less ideal than if the scissor mechanism worked.

Prototyping

Approach 1: We attempted to 3D print a linear actuator but learned printing gear mechanisms is challenging espeically when using someone else’s files. The linear part got stuck in the mechanism.

So then we tried to 3D print the scissor mechanism and after attaching it to a servo we had luck getting it to work. Our deduction is that this was a really tiny, fine space so the 3D printing had to be incredibly accurate.

Approach 2: We pivoted and attempted to create a scissor linear actuator instead. We 3D printed it and used M3 nuts and screws to assemble

PXL_20260213_210537489.mp4

We ran into a lot of issues with friction when testing our mechanism and trying to get it to behave consistently. Troubble shooting:

We decided to re 3D print the mechanism on better printers and add washers between the joints. This helped improve it significantly. So the idea is to attach both sides of this mechanism to a rigid wall. The box itself will be made out of biomaterials. The rigid walls will be tucked in to either side of the box.

PXL_20260225_214937630.mp4

BioMaterials

We want to make the cube out of an agar agar bio composite material. The tests and findings are as follows.

Approach 1 Agar Agar Glycerin Sheet:

Recipe:

8 grams of Agar
13.5 grams of Glycerin
400 ml of water

Observations & Objective:

We were able to achieve a full sheet with minimal strinkage. Goal now is to figure out how to make the sheet thicker and more rigid so it can actually hold a cast of a box instead of just using the sheets to decorate the box.

After about a week of drying

Approach 2 Agar Agar, Glycerin, Psyllium, Calcium Carbonate Mold Box:

Recipe:

Water: 180 g
Agar: 5–6 g
Glycerine: 6–8 g
Calcium carbonate: 8–12 g
Psyllium 1 g (for crack resistance)

Casted into a small, cube mold

Observations & Objective: The problem here is that the solid mass is only 11.5% I had the box air drying the bottom was exposed. Likely, this caused some pull on the sides of the wall, cracking the bottom. So future iterations, we will need to slow down the drying in the first 24 hours, then release it from the mold and continue air drying. I also thought maybe a stronger filler would help get the structural properties we’re looking for.

After about a week of drying

After over a week of drying

Approach 3 Agar Agar, Glycerin, Wood Flour Filler:

Recipe:

400ml water
16g agar
10g glycerin
40g of wood flour

Observations & Objective: We wanted to try a stronger filler. The solid mass was only 14% in this recipe so likely still not enough. We should be targeting 25-30%. This leads to the shriveling and warping that’s happening. All the water is being evaporated and sucked up, a higher solid mass would help the fillers do their job better. Also, this would produce a texture too rigid for our purposes. We want something more flexible. The uneven drying leads to warping. Not sure how to avoid the warping concern yet.

Picture right after casting

Picture after the sheet has dried

Approach 4 Back to Agar Agar, Glycerin, but Cast to Cube Mold:

Recipe:

400 ml water
8g Agar
18g glycern
Gauze around the center of the cube

I put a bowl over the mold after casting to let it evaporate slowly for the first 24 hours

Observations & Objective: I was having a hard time with the fillers, so I thought to go back to just the basic recipe. But to verify it, I dried it for a bit in the induction oven and realized it was starting to warp. (Image on the right). However, if we can keep it from drying out completely, this partly wet cube could serve our purposes well because the walls are flimsy enough without tearing. We can control it from drying to much by placing it in a bag (avoid humidity) and placing it in the fridge (avoid drying).

24 hours after casting, initial demolding

After drying for a bit in the induction oven

pproach 5 Agar, Glycerin, MCC, Calcium Chloride: Last ditch effort to try fillers:

Recipe:

600 ml water
15g agar
20g glycerin
30g MCC
30g Calcium Chloride
Gauze around the center of the cube

Observations & Objective: We got extremely lucky with this last try, it was the perfect balance of flexible and sturdy. What I learned:

Untitled spreadsheet

Sewing

I sewed into the agar agar box and into the MCC material. The agar agar box was more prone to tearing, making the MCC a better option. The MCC is also super flexible with the gauze even after multiple days of drying and didn’t significantly warp.

Agar Agar

MCC Mix

The cardboard is more likely to work to hold our mechanism than the paper plate. May need to try more rigid plates, however.

Final Casting

We ordered a silcone mold that would be large enough to fit our mechanism. Our options were quite limited and would result in more of a rectangular box than a cube but for the sake of getting something suitable for our mechanism we dd a large casing.

We did not like that mold. The scale, gem shape was going to lead ot telling a completely different story. So we got a new mold. But in the process realiazed how unstatisified we felt as well with giving up the vision of final version being an acutal cube.

So our problem was that we had this beautiful mechanism we spent a lot of time getting just right and working well that was to big for the molds we wanted. But the molds we could get to fit the mechanism didn’t fit our vision for the final version.

Solution (which we tried really hard to avoid) venture into 3D printing and see if I can scale down the mechanism

In the meatntime I created and casted to our ideal mold size.

Note: Since I did notice that the previous test strips/molds were starting warp, I decided to leave our cube mold in the fridge to significantly slow down drying so we could have more control over it’s life span

3D Modeling & Printing

I had doubts early on about scaling because I recall from intro to fab that it’s not as easy as clicking a scaling corner and dragging down. Some things that were fixed where the servo size hole. But that means the legs couldn’t be changed much either otherwise they would become unproportional. So I thought, the only way to proceed is to get a smaller servo. We we got a SG90 servo to build off of.

Low and behold it worked! One thing to note, I made M3 sized holes but the M3 screws couldn’t fit. Here we are using M2 screws and washers, however they were also pretty lose. I suspect the solution to this would be to create a hole slight smaller than M2 to have a pressure fit.

We tested the mechanism to make sure the servo had enough torque to rotate the mechanism with the servo head. And it worked! Breakthrough!

IMG_6956.mov

IMG_6957.mov

Putting it All Together

One unfortuate learning came as we put everything together. The mechanism with this small motor was not strong enough to push the walls of the mold. This motor doesn’t have enough torque to push back against any small force on it. We had A LOT of difficulty getting the PERFECT combo of: smooth scissor mechanism + a mechanism that fits within the walls of the cube + a scissor mechanism strong enough to move the walls of the cube. Unfortuantely we forgot to capture this part in our documentation. My stubborness I didn’t want to give up the tiny version of our mechanism but we were blocked with how to work around it.

With the help of some of our amazing peers, they pointed out the only important part of the mecahnism is the servo head comming out and the servo being stable in some way. The servo doesn’t necessarily need a snug pocket to fit as in the way it’s currently designed. This opens up the option to using the small mechanism with the large servo.

Redesign [3D model images here]

Several Servo Motor + Mechanism Prototypes we iterated over

The main thing to take away here is we tried to use a screw to connect to a servo head to fit the mechanism. But then we standded the part where the servo connects and then it fit a head that is ideal for this servo. Having the elevated screw and servo head was less optimal because we begaan to realize that it barely fit in our cube mold. So we had to find a way to reduce height. While it helped a lot the mecanism was still a bit too tall to fit in the cube and put the mold on top. (Can’t escape the contraints!) Since we had already casted to the mold and had no control over how it was made, I go creative in adding some height to the lid with superglue and some scrap pieces.

Test

We created a hole in the mold for the Lidr sensor. We wrote code to create an idle breathing for the cube, light pulses from the servo against the walls. And a small expansion when someone approachs and contraction when someone goes away.