Max — Technical Dossier: Robotic Endgame

01 — Overview

The Concept

Domestic robotics has historically been built on a purely utilitarian paradigm: vacuuming floors, sorting items, automating tasks. The Bumps Project explores a radically different path: the robotics of pure relationship. Designing an artificial companion of barely 12 centimeters, devoid of obvious practical functions, may seem paradoxical. Yet, it is precisely in this apparent 'uselessness' that the fantastic nature of this approach lies. By freeing itself from functional constraints, the machine becomes an object of pure empathy. Animated by the organic silence of Nitinol muscles and endowed with subtle tactile reactivity, it ceases to be a tool and becomes a manifestly living presence. It is the introduction of a poetic breath into the home: a small mechanical being that accomplishes nothing, but whose simple existence and feigned vulnerability awaken a deep and instinctive emotional connection within us.

Max is a 12 cm autonomous companion micro-robot with the appearance of a round and pudgy olive-green organic creature, with large bulbous black eyes and two thin curved antennae. Beneath its silicone skin lies a 3D-printed endoskeleton, Nitinol artificial muscles, and remote intelligence.

🧬

Organic Biomimicry

Hunched posture, passive pendular gait, facial micro-expressions. Every movement is designed to look natural and alive, not mechanical.

🧠

Remote Intelligence

The onboard ESP32-S3 manages local perception and reflexes. Complex reasoning is offloaded to a server via Wi-Fi — the 'Symbiotic Host' architecture.

🤫

Absolute Silence

No geared motors. All movements are produced by artificial muscles (Nitinol, LCE) and a piezoelectric motor — zero audible mechanical noise.

🛡️

Passive Atony Protocol (PAD)

In case of danger or pressure > 45N, the ER fluid solidifies, the muscles relax, and Max "goes limp" — mimicking an animal playing dead.

🔋

Charging Sans Contact

Li-S 1200 mAh battery rechargeable par induction Qi. Max revient instinctivement vers son « nid » de recharge quand l'énergie est basse.

🖐️

Tactile Skin (EIT)

16 electrodes in the silicone skin allow touch detection all over the body with a 2-3 mm resolution. Max 'feels' when it is petted.

02 — Concept Art

Robot Visualizations

Six AI-generated technical illustrations, from engineering blueprints to cinematic portraits, covering every angle of Max.

Anatomical Front Cutaway

Endoskeleton, Nitinol muscles, battery, ESP32-S3

Hip Kinematics

Ball-joint, Nitinol, Dyneema, MEP — patent style

Thermal Dissipation System

Gradient 70°C → 25°C: muscles → copper → antennae

Full Sagittal Cutaway

Hunched posture, tungsten pendulum, piezo motor

Modular Exploded View

6 sub-assemblies: head, neck, trunk, pelvis, legs

Expressive Portrait

Living Max: CMOS eyes, articulated antennae, amber skin

Head & Neck Module (Physical)

Titanium skull, 25µm conjugate mobile eyes, h-BN helical neck

Upper Limb & Hand

Underactuated 3-finger hand, Dyneema tendon, 50µm Nitinol muscle

Pelvis & Legs Module

Piezo cam, rotary motor, 15g tungsten pendulum, silicone legs

12cm Assembled Endoskeleton

Hunched PLA structure, titanium skull, Nitinol muscles, and h-BN sheaths

03 — Internal Structure

Biomechanical Architecture

Beneath its round and pudgy olive-green creature appearance, Max is built in concentric layers, from the central rigid endoskeleton to the tactile skin on the surface.

Breakdown by Body Zone

🧠 Head (Titanium Skull)

DMLS machined titanium skull (thermal heatsink)
2× CMOS OV2640 micro-cameras (eyes)
2× MEMS ICS-43434 microphones (ears)
ESP32-S3-WROOM-1 (local brain)
CML CM824 driver (8 SMA channels)
6× SMA Bimorph 10mg (micro-expressions)
2× methanol heat pipe antennae

🦴 Neck (Cervical Region)

Atlanto-occipital joint (brass ball-joint)
4× Nitinol 50µm muscles (head tilt)
Silicon sheaths filled with h-BN (thermal)
I²C + PWM connector (8 pins)

🫁 Trunk (Thoracic Hump)

Hunched PLA/PETG endoskeleton (FDM print)
Subcutaneous copper braids (thermal)
4× passive ventilation channels
2× LCE actuators (simulated breathing)
EIT module 16 electrodes (tactile)

⚖️ Pelvis (Center of Gravity)

Eccentric camshaft (stainless steel)
Rotary piezoelectric motor (silent)
15g tungsten pendulum (ultra-low CG)
Li-S 1200 mAh battery
Qi receiver coil ø20mm
DC-DC converter

🦿 Legs (×2)

Coxofemoral joint (brass ball-joint)
2× Nitinol 75µm muscles (flexion)
Dyneema 0.1mm tendon (passive return)
MEP micro-clutch (locking)
Electrorheological fluid (knee, PAD)
Curved silicone foot (passive rolling)

🧤 Skin (Global Envelop)

Silicone RTV Ecoflex 00-30 (~2mm)
Translucent olive-green tint
Integrated graphene capacitive sensors
DEA membranes (skin twitching)
Distributed EIT network (proprioception)

04 — Materials & Actuators

Actuation Technologys

Max uses a hybrid architecture combining 6 different actuation technologies, each optimized for a specific type of motion.

Global Comparative Table of Technologys

Technology	Force	Speed	Silence	Energy	Mass	Heat	Max Application
Nitinol SMA (50µm)	★★★★★	★★☆☆☆	★★★★★	★☆☆☆☆	★★★★☆	★☆☆☆☆	Main muscles
SMA Bimorph (10mg)	★★★☆☆	★★★☆☆	★★★★★	★★☆☆☆	★★★★★	★★☆☆☆	Micro-expressions
LCE (Élastomère LC)	★★☆☆☆	★☆☆☆☆	★★★★★	★★☆☆☆	★★★★★	★★☆☆☆	Simulated breathing
MSMA (Magnétique)	★★★☆☆	★★★★★	★★★★☆	★★★☆☆	★★★☆☆	★★★★★	Antennae (>50 Hz)
DEA (Diélectrique)	★★☆☆☆	★★★★★	★★★★★	★★★★☆	★★★★★	★★★★★	Skin twitching
Piézo Rotatif	★★★★☆	★★★★☆	★★★★★	★★★★★	★★★☆☆	★★★★★	Walking motor
Fluide ER	N/A (blocage)	★★★★★	★★★★★	★★★★☆	★★☆☆☆	★★★★★	PAD locking

Nitinol — The Main Muscle

Properties of Nitinol (Flexinol)

Activation temperature (Af)40-45°C
Power density100 W/g
Useful stroke3-5%
Recommended diameter25-100 µm
Passive cooling (50µm)500 ms
Silicone/h-BN cooling (50µm)150 ms

h-BN Loaded Silicone — Ceramic Dissipation

Boron Nitride (h-BN) loaded silicone is a safe and viable alternative to LMPE. Fully electrically insulating (zero risk of short circuit) and inert (no copper corrosion), it offers excellent thermal conductivity of 1.5 to 3 W/m·K.

Cooling gain×2 à ×3
Possible contraction frequency4-5 Hz
FabricationDIY (RTV + h-BN Powder Blend)

05 — Locomotion

Passive Walking Kinematics

Max walks using a passive inverted pendulum model coupled with pelvic roll generated by an eccentric cam — an energy-efficient system inspired by human walking.

🔄 Inverted Pendulum

The legs swing naturally under gravity. The natural frequency of 2.66 Hz is dictated by the leg length (35mm) and gravity.

Period375 ms
Frequency2.66 Hz

⚙️ Eccentric Cam

A silent rotary piezo motor drives an eccentric camshaft (3mm offset) that transfers energy to the tungsten pendulum, causing the pelvic roll for walking.

Eccentricity3.0 mm
Pelvic roll4.9°

🦶 Walking Results

Simulations show stable walking with an ultra-low Cost of Transport (CoT) of 0.1 — more efficient than most current bipedal robots.

Step length26.8 mm
Speed71.4 mm/s
CoT0.0995
Peak GRF1.01 g
Hip torque10.51 mN·m
Energy / pas2.09 mJ

06 — Electronics

Brain & Wiring

Max's brain is an ESP32-S3 that controls muscles via the CM824 driver, reads sensors via I²C and SPI, and communicates with the host via Wi-Fi.

Wiring Diagram

graph LR
    subgraph Power["⚡ Power Supply"]
        BAT["🔋 Li-S 3.7V"]
        DCDC["DC-DC 5V"]
        LDO["LDO 3.3V"]
    end

    subgraph Brain["🧠 Brain"]
        ESP["ESP32-S3"]
        CM824["CM824 Driver"]
    end

    subgraph Sensors["👁️ Sensors"]
        CAM["CMOS Cameras ×2"]
        MIC["MEMS Microphones ×2"]
        IMU["6-axis IMU"]
        EIT["EIT 16 elect."]
        TOF["VL53L0X ToF"]
    end

    subgraph Actuators["💪 Actuators"]
        NECK["Neck ×4 wires"]
        HIP["Hips ×4 wires"]
        FACE["Face ×6 SMA"]
        PIEZO["Rotary Piezo"]
        ER["ER Fluid ×2"]
        MEP["MEP ×2"]
    end

    BAT --> DCDC --> LDO --> ESP
    BAT --> CM824
    ESP -->|"I²C"| IMU
    ESP -->|"I²C"| EIT
    ESP -->|"I²C"| TOF
    ESP -->|"SPI"| CAM
    ESP -->|"ADC"| MIC
    ESP -->|"SMA_CTRL"| CM824
    CM824 --> NECK
    CM824 --> HIP
    CM824 --> FACE
    ESP -->|"GPIO"| PIEZO
    ESP -->|"GPIO"| ER
    ESP -->|"GPIO"| MEP

CM824 PWM Channels

Channel	Function	Wire	Zone
CH1	Neck — Forward flexion	Nitinol 50µm	Neck
CH2	Neck — Rear extension	Nitinol 50µm	Neck
CH3	Left hip — Flexion	Nitinol 75µm	Left Leg
CH4	Left hip — Extension	Nitinol 75µm	Left Leg
CH5	Right hip — Flexion	Nitinol 75µm	Right Leg
CH6	Right hip — Extension	Nitinol 75µm	Right Leg
CH7	Face — Expression A	SMA Bimorph	Head
CH8	Face — Expression B	SMA Bimorph	Head

07 — Thermal Management

The Thermal Nightmare

The Joule effect from Nitinol muscles generates heat trapped in the insulating silicone casing. The multi-layer thermal system dissipates this energy from the inside out to the antennae.

Dissipation Chain

graph LR
    A["🔥 Nitinol 70°C"] -->|"Contact"| B["🟢 Gaine Silicone/h-BN"]
    B -->|"Conduction"| C["🟠 Tresses Cuivre"]
    C -->|"Conduction"| D["⚪ Crâne Titane"]
    D -->|"Caloducs"| E["🔵 Antennae Méthanol 25°C"]
    F["💨 Canaux Ventilation"] -->|"Convection"| C

    style A fill:#cc3333,stroke:#ff4444,color:#fff
    style B fill:#338833,stroke:#44aa44,color:#fff
    style C fill:#cc8833,stroke:#ddaa44,color:#fff
    style D fill:#888888,stroke:#aaaaaa,color:#fff
    style E fill:#3366cc,stroke:#4488ee,color:#fff
    style F fill:#33aacc,stroke:#44ccee,color:#fff

Thermal Simulation Results

❄️ Passive Cooling

Equilibrium temperature37.93°C

Cooling time500 ms

Frequency max1.8 Hz

StatusSAFE

🌡️ Active Cooling

Equilibrium temperature25.98°C

Cooling time500 ms

Frequency max1.8 Hz

StatusSAFE

🧊 h-BN Cooling (DIY)

Equilibrium temperature25.10°C

Cooling time150 ms

Frequency max4.8 Hz

StatusSAFE

08 — Power Supply

Energy System

High-density Lithium-Sulfur battery with Qi induction charging. Three usage scenarios for a battery life of 3.4 to 24 hours.

😴 Idle Mode

Power consumption50 mA

Battery Life24.0 h

Capacity4.44 Wh

🚶 Normal Walking

Power consumption180 mA

Battery Life6.67 h

Capacity4.44 Wh

🏃 Intense Movement

Power consumption350 mA

Battery Life3.43 h

Capacity4.44 Wh

🔋 Battery Specifications

ChemistryLi-S (Lithium-Soufre)
Capacity1200 mAh
Nominal voltage3.7 V
Energy4.44 Wh
Mass8.0 g
ChargingQi wireless (5V)

09 — Construction

Assembly Sequence

The V1 prototype is built from the inside out in 12 steps, from the 3D printed endoskeleton to flashing the firmware.

Print endoskeleton (PLA/PETG)

FDM printing of the hunched spine, skull support, and leg bones. ~5g of material.

Assemble joints

Mount brass ball-joints (neck, hips) and the eccentric camshaft in the pelvis.

Install Li-S battery

Position the 1200 mAh cell in the pelvic cavity, above the tungsten pendulum.

Wire power rail

Connect DC-DC Boost + LDO 3.3V + Qi coil. Verify voltages (3.3V, 3.7V, 5V).

Mount ESP32-S3 in skull

Secure module on the Flex PCB and place it in the titanium skull cavity.

Connect CM824 & route SMA wires

Solder the 8 driver channels to the output connectors. Prepare Nitinol wire routing.

Install Nitinol muscles + h-BN sheaths

Route 50µm (neck) and 75µm (hips) wires along the endoskeleton. Envelop in h-BN loaded silicone sheaths.

Install Dyneema tendons & MEP

Install passive return tendons and electro-permanent micro-clutches at the hips.

Integrate thermal copper braids

Route subcutaneous braids from muscle zones to the titanium skull (heatsink).

Install sensors

Mount CMOS cameras, MEMS mics, IMU, ToF, and 16 EIT electrodes in their respective positions.

Neckler la peau en silicone RTV

Use negative mold to cast Ecoflex 00-30 tinted green-olive around the assembly. Cure time: 4h.

Flash ESP32 firmware & calibrate

Upload firmware via USB-C, calibrate IMU, EIT thresholds, and sensorless SMA control curves.

10 — Bill of Materials

Bill of Materials (BOM)

Complete list of 57 components required to build the V1 prototype, with mass, estimated price, and supplier.

Component	Qty	Mass	Prix	Supplier
⚡ Electronics & Control
ESP32-S3-WROOM-1 (N8R8)	1	1.5g	4.50€	Espressif / Mouser
CML CM824 SMA Driver (8ch)	1	0.3g	12.00€	Cambridge Mechatronics
MPU-6050 6-axis IMU	1	0.1g	2.50€	InvenSense
AD5933 Impedance (EIT)	1	0.1g	8.00€	Analog Devices
VL53L0X Time-of-Flight	1	0.1g	3.50€	STMicroelectronics
TPS61200 DC-DC Boost	1	0.2g	2.00€	Texas Instruments
MCP1700 LDO 3.3V	1	0.1g	0.50€	Microchip
Custom 4-layer Flex PCB	1	0.8g	15.00€	JLCPCB Flex
👁️ Sensors
OV2640 Micro-Caméra CMOS	2	0.6g	6.00€	OmniVision
ICS-43434 Micro MEMS	2	0.1g	4.00€	TDK InvenSense
EIT Electrodes (flex copper)	16	0.32g	1.60€	Custom PCB
💪 Actuators
Wire Nitinol Flexinol 50µm (1m)	2	0.2g	16.00€	Dynalloy
Wire Nitinol Flexinol 75µm (1m)	1	0.3g	10.00€	Dynalloy
SMA Bimorph 10mg (custom)	6	0.06g	30.00€	Lab-fabricated
Moteur piézo rotatif	1	1.2g	45.00€	PCBMotor ApS
MEP Micro-Embrayage	2	1.0g	30.00€	Custom (NdFeB+AlNiCo)
🦴 Structure & Mechanics
Crâne Titane (DMLS)	1	3.0g	80.00€	Shapeways
PLA/PETG Endoskeleton	1	5.0g	2.00€	Local 3D Printing
Tungsten Pendulum ø16mm	1	15.0g	12.00€	Midwest Tungsten
Eccentric cam (stainless steel)	1	1.0g	5.00€	Usinage CNC
Articulated ball-joints (brass)	5	2.0g	10.00€	MicroFasteners
🧤 Soft Materials
Silicone RTV Ecoflex 00-30	1	18.0g	15.00€	Smooth-On
Wire Dyneema 0.1mm (5m)	1	0.2g	5.00€	Beadsmith
Copper braid 0.5mm (2m)	1	2.0g	3.00€	Électronique
Boron Nitride Powder (h-BN)	1	1.5g	12.00€	DIY (RTV + h-BN Blend)
🔋 Energy
Batterie Li-S 1200mAh	1	8.0g	35.00€	Oxis Energy
Qi receiver coil ø20mm	1	1.5g	4.00€	Wurth Elektronik
🌡️ Thermal
Heat-pipe méthanol ø2mm 30mm	2	1.6g	16.00€	Celsia
TOTAL	57	65.8g	389.60€	Mass budget: 80g max → margin 14.2g ✅

11 — Simulations

Simulation Results

Synthesis of results from the chimera_analyst.py v2 script covering thermal, autonomy, kinematics, and mass budget.

🌡️ Thermal Simulation

Wire Nitinol 50µm, courant 0.4A, impulsion 50ms @ 2Hz

Resistance (10cm)56.02 Ω

Instantaneous power8.96 W

Average power0.896 W

Duty cycle10%

Equilibrium temp (passive)37.93°C

Equilibrium temp (h-BN)25.10°C

🚶 Walking Simulation

Inverted pendulum, legs 35mm, mass 80g

Period pendulaire375 ms

Steps per second2.7

Step length26.8 mm

Speed71.4 mm/s

CoT0.0995

Energy / pas2.09 mJ

⚖️ Budget Mass

Distribution by category

Structure26.0g (39.5%)

Soft materials21.7g (33.0%)

Energy9.5g (14.4%)

Électronique3.2g (4.9%)

Actionneurs2.76g (4.2%)

Remaining margin14.2g

12 — Technical Diagrams

Diagrammes d'Ingénierie

Interactive structural diagrams covering internal anatomy, hip biotensegrity, and modular exploded view.

Neckpe Anatomique & Structure Interne

graph TD
    subgraph Head["🧠 Head"]
        A["Yeux CMOS ×2"]
        B["MEMS Microphones ×2"]
        C["ESP32-S3 + CM824"]
        D["Antennae Caloducs"]
    end

    subgraph Neck["🦴 Neck"]
        E["Rotule Atlanto-Occipitale"]
        F["Nitinol 50µm ×4"]
    end

    subgraph Torso["🫁 Tronc"]
        G["Endosquelette Cyphose"]
        H["Tresses Cuivre"]
        I["Ventilation Passive"]
    end

    subgraph Pelvis["⚖️ Bassin"]
        J["Came Excentrique"]
        K["Pendule Tungstène 15g"]
        L["Batterie Li-S"]
        M["Bobine Qi"]
    end

    subgraph Legs["🦿 Membres"]
        N["Hanches Coxofémorales"]
        O["Dyneema + MEP"]
        P["Pieds Incurvés"]
        Q["Peau Graphène"]
    end

    C -->|"PWM"| F
    C -->|"Moteur"| J
    J -->|"Came"| K
    K -->|"Bascule CG"| P
    Q -->|"Tactile"| C
    H -->|"Thermique"| D

Exploded View — 6 Modules

graph TD
    subgraph M1["Module 1 : Head"]
        M1A["Crâne Titane"]
        M1B["Antennae ×2"]
        M1C["ESP32-S3"]
        M1D["CM824"]
    end

    subgraph M2["Module 2 : Neck"]
        M2A["Rotule"]
        M2B["Nitinol ×4"]
        M2C["Gaine h-BN"]
    end

    subgraph M3["Module 3: Trunk"]
        M3A["Squelette PLA"]
        M3B["Cuivre"]
        M3C["LCE ×2"]
        M3D["EIT"]
    end

    subgraph M4["Module 4: Pelvis"]
        M4A["Piézo + Came"]
        M4B["Tungstène"]
        M4C["Li-S + Qi"]
    end

    subgraph M5["Module 5 : Left Leg"]
        M5A["Hanche"]
        M5B["Nitinol 75µm"]
        M5C["ER Genou"]
    end

    subgraph M6["Module 6 : Right Leg"]
        M6A["Hanche"]
        M6B["Nitinol 75µm"]
        M6C["ER Genou"]
    end

    M1 ---|"Rotule + I²C"| M2
    M2 ---|"Colonne + PWM"| M3
    M3 ---|"Bassin + Power"| M4
    M4 ---|"Hanche G"| M5
    M4 ---|"Hanche D"| M6

    style M1 fill:#E8F0FE,stroke:#4285F4,color:#1C1612
    style M2 fill:#E6F4EA,stroke:#34A853,color:#1C1612
    style M3 fill:#FCE8E6,stroke:#EA4335,color:#1C1612
    style M4 fill:#FEF7E0,stroke:#FBBC04,color:#1C1612
    style M5 fill:#F3E8FD,stroke:#AB47BC,color:#1C1612
    style M6 fill:#F3E8FD,stroke:#AB47BC,color:#1C1612