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 Agar biocomposite that 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: Biocomposites,, Bambu Studio, Microcontroller, Actuators

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

My role: Creating Biocomposite, 3D Modeling, Linear Actuator

Status: Completed, Github

Contents:

Mechanical Mechanism

BioMaterials

3D Modeling & Printing

Putting it All Together

View Final Media

Process

Mechanical Mechanism

Initially, we wanted a moving mechanism inside the box. We explored ideas like a motor with offset weights.

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

The gyroscope seemed too heavy and difficult to stop. Vibrational motors kept coming back, so two prototype ideas:

Place four weights on the corners of the box and see if they move it slightly.
Explore a solenoid.

Feedback: Use existing motion mechanisms instead of recreating them, and focus on enclosing and hiding them.

Other potential tries:

3. Explore existing rotation or linear mechanisms under the box.

4. Control a ball bearing with a sensor or motor and cover it.

Pivot to moving walls (Linear Actuators)

Click for references to research on linear actuators

Rack and pinon:

Other potential Linear Actuators (Scissors):

Wedge:

[wall ] /\ [ wall ]

wedge

Slider Crank:

Prototyping

Approach 1: We 3D printed a linear actuator, but the gear mechanism kept getting stuck. Printing precise gear systems that rely on a fine space to work from existing files was difficult.

Approach 2: We pivoted fully to a scissor linear actuator

During testing, friction caused inconsistent movement.

After troubleshooting, we reprinted the mechanism on better printers and added washers between the joints, which made it work A LOT better.

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 test how to make the sheet thicker and more rigid so it could hold a box mold instead of just decorating a structure.

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 solid mass (~11.5%) was too low. Air drying exposed the bottom, pulling on the walls and causing cracks. Future iterations need slower drying in the first 24 hours, then demolding and continued air drying. Stronger fillers may also help.

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: Solid mass (~14%) was still too low. Target should be 25–30%. Low solids caused shriveling and warping as water evaporated. The texture also became too rigid for our needs.

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: Rapid drying caused warping, but a partially wet cube worked well because the walls remained flexible. Drying can be controlled by storing in a sealed bag in the fridge.

24 hours after casting, initial demolding

After drying for a bit in the induction oven

Approach 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: This produced the best balance of flexibility and strength

Untitled spreadsheet

Sewing

I sewed into the agar agar box and into the MCC material. The agar agar box tore easily/ The MMC material held stitches better, remained flexible after drying, and warped less.

Agar Agar

MCC Mix

For supporting the mechanism, cardboard worked better than the paper plate, though may need rigid plates

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.

We switched molds, but still felt unsatisfied—we wanted a true cube.

Problem: our mechanism worked well but was too large for ideal molds, while suitable molds didn’t match our vision

Solution: scale down the mechanism (which we tried to avoid).

In the meantime, I cast a cube in our ideal size and slowed drying by storing it in the fridge for more control.

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 about scaling due to fixed parts (like the servo hole). Instead, we switched to a smaller SG90 servo.

Bambu Studio: Scaled down 58% and included negative parts to recreate holes for screws

The scaled mechanism worked. However, M3 holes were too small for M3 screws; M2 screws fit but were loose. A slightly smaller hole would allow a pressure fit.

We confirmed the servo had enough torque to drive the mechanism—breakthrough!

IMG_6956.mov

IMG_6957.mov

Putting it All Together

The smaller motor wasn’t strong enough to push the cube walls. We struggled to balance:

Smooth scissor motion
Fit within the cube
Enough force to move the walls

With peer feedback, we realized the servo only needed to be stable, not tightly enclosed. This allowed us to pair the small mechanism with a larger servo.

Redesign with Bambu Studio:

Experimented with a larger opening at the bottom to sit on the large servo. Failed because the mechanism didn`t have enough space to rise and rotate at that point.

Creaative more negative parts to try to enlarge the servo head hole

Ultimately sanding and tape were most effective in getting our mechanism to stabalize 😂

Several Servo Motor + Mechanism Prototypes we iterated over:

Key change: instead of using a raised screw connection, we switched to a better-fitting servo head to reduce height by sanding out the opening so the better-fitting sero head would fit. Even then, the mechanism was slightly too tall, so we added height to the lid using scrap pieces and superglue.

Test: We added a hole for the LiDAR sensor and programmed: Idle “breathing” motion, Light wall pulses, and Expansion when someone approaches, contraction when they leave