Final Project

Assignment

Individual assignment
  • Your project should incorporate: 2D and 3D design, Additive and subtractive fabrication processes, Electronics design and production, Embedded microcontroller interfacing and programming and System integration and packaging.
01 — What will it do?
The core concept and function of the project

The Octopus Arm is a soft-robotic adaptive gripper designed as a modular end-effector for a UR3 robotic arm. Inspired by the fluid, multi-axis bending of octopus tentacles, it replaces traditional rigid grippers with three flexible TPU tentacles that naturally conform to the geometry of any object, from spheres to irregular shapes, without requiring complex force-feedback algorithms.

The system operates through a wireless glove interface: the user wears a glove instrumented with three flex sensors. Bending a finger transmits the angle wirelessly via BLE to the gripper, which replicates that motion through servo-driven Dyneema tendons running along each tentacle's spine.

Adaptive GraspingTPU tentacles conform to any object geometry without rigid constraints
Wearable ControlFlex-sensor glove maps finger bends to tentacle angles in real time
BLE Wireless Link20 Hz update rate, <50 ms latency over 2.4 GHz
UR3 End-effectorCustom flange adapter, plug-and-play mounting on the robot arm
02 — Who's done what beforehand?
Prior art, related research, and existing work

Soft robotic grippers have been explored extensively in academia and industry. Key references that informed this project:

  • Harvard Soft Robotics Toolkit, open-source actuators using pneumatic silicone fingers; inspiration for tendon-driven alternatives without air compressors.
  • Festo Bionic Cobot, commercial soft gripper using 3D-printed flexible structures, demonstrating viability of FDM for end-effectors.
  • OpenBionics, low-cost anthropomorphic hands using TPU and Dyneema tendons; direct precedent for this project's actuation method.
  • MIT Media Lab, Fiber Reinforced Actuators, research on segmented flexible actuators with embedded fiber constraints, influencing the vertebrae design.
  • Previous Fab Academy projects, glove-based BLE controllers showed the viability of XIAO ESP32 for low-latency wireless sensing.

Key differentiator: this project combines tendon-driven TPU tentacles with a wireless flex-sensor glove and direct UR3 integration, a combination not found as a single, open-source, Fab-fabricated system.

03 — What sources will you use?
References, documentation, and learning resources
04 — What will you design?
2D, 3D, electronics, and software design outputs
  • Tentacle geometry, parametric Autodesk Inventor model with 12 vertebrae per tentacle, configurable hinge stiffness via wall thickness. Tendon channel integrated into spine.
  • Gripper hub, 3-axis mount holding all three tentacles at 120° spacing, servo bay, and custom flange pattern for UR3 coupling.
  • Wearable glove frame, 3D-printed TPU dorsal strap with routed channels for flex sensor wiring; minimizes constraint on hand movement.
  • Custom PCBs ×2, Glove board: XIAO ESP32-C3 + 3× JST flex sensor headers + LiPo charger. Gripper board: ESP32-C3 + 3× servo headers + power regulation.
  • Firmware, BLE GATT service (Arduino), ADC calibration, servo PWM via LEDC, moving-average filter, watchdog reconnection logic.
  • 3D-printed servo bracket, PLA mounting bracket for servo bay, printed on Bambu X1E.
    • 05 – 07 · Materials, components & costs
    What will be used, where it comes from, and how much it costs
    ComponentQtySource Unit CostTotalMake / Buy
    XIAO ESP32-C32Seeed Studio$5.90$11.80Buy
    Flex Sensor 2.2"3Adafruit / SparkFun$12.00$36.00Buy
    SG90 Servo Motor3Local electronics$2.50$7.50Buy
    LiPo 3.7V 500mAh1Amazon / local$8.00$8.00Buy
    22kΩ Resistors3Lab stock$0.05$0.15Buy
    TPU 95A Filament200gLab / Polymaker—$8.00Buy
    PLA Filament (hub)100gLab stock—$2.50Buy
    Dyneema 0.3mm cord3mFishing supply—$2.00Buy
    Custom PCB ×2 (FR4)2Fab Lab — milled—$6.00Make
    PLA — Servo bracket1Lab stock—$1.00Make
    JST-PH connectors10Lab stock$0.20$2.00Buy
    SMD passivesassortedLab stock—$1.50Buy

    Estimated total: ~$86.45 USD  |  Fabricated in-lab: PCBs, tentacles, hub, bracket, glove frame

    08 — What parts and systems will be made?
    Fabricated vs purchased breakdown — "make rather than buy"
    TPU Tentacles ×33D printed, 12-vertebrae segmented design with tendon channel
    Gripper HubPLA 3D print, 120° servo bay + custom UR3 flange adapter
    Glove FrameTPU dorsal exoskeleton with wire routing channels
    Custom PCBs ×2FR4, milled on Roland MDX-50, glove board + gripper board
    Servo BracketPLA 3D-printed servo mounting plate, Prusa MK4
    Firmware (both boards)Arduino/ESP-IDF, BLE, ADC, PWM, filter logic
    09 — What processes will be used?
    Fabrication and design workflows from design to system integration
    1
    PCB Design — Fusion 360PCB schematics, board layout, Gerber export for Roland MDX-50
    2
    3D Design — Autodesk InventorParametric tentacle vertebrae, gripper hub, glove frame, UR3 adapter
    3
    Additive Fabrication — FDM 3D PrintingTPU 95A tentacles + glove frame; PLA gripper hub and adapter (X1E)
    4
    Subtractive Fabrication — PCB MillingRoland MDX-50 CNC mill, 0.4mm V-bit traces on FR4 copper board
    5
    Additive Fabrication — Servo BracketPLA servo mounting bracket printed on X1E
    6
    Electronics Production — SolderingSMD reflow + hand soldering; continuity test before power-up
    7
    Embedded Programming — Arduino IDE / ESP-IDFBLE firmware, ADC calibration, servo PWM, OTA update support
    8
    System Integration & TestingEnd-to-end BLE loop test, latency measurement, grip force characterization on UR3
    2D & 3D Design Additive Fabrication Subtractive Fabrication (PCB) Electronics Design Microcontroller Programming System Integration
    10 — What questions need to be answered?
    Open problems and research directions
    • What is the minimum tendon cross-section (Dyneema diameter) that can sustain 0.8 N servo force over 500 actuation cycles without creep or breakage?
    • How does TPU 95A print orientation (flat vs vertical vertebrae) affect bending stiffness and maximum grip angle of each tentacle?
    • Can the BLE connection maintain <50 ms latency in the presence of the UR3's servo motor EMI and a dense 2.4 GHz lab environment?
    • What is the optimal hinge thickness (0.8 mm vs 1.2 mm vs 1.6 mm) to balance flexibility and structural integrity under repeated bending?
    • Is a 10-sample moving-average ADC filter sufficient to remove flex sensor noise, or does a Kalman filter improve perceived smoothness?
    • Can the LiPo 3.7V 500mAh battery power both glove electronics and servos for a minimum 30-minute continuous operation session?
    • How should the UR3 coordinate frame interact with tentacle actuation, should grip and positioning be fully decoupled or partially coupled?
    11 — How will it be evaluated?
    Success criteria and performance benchmarks
    BLE LatencyEnd-to-end <50 ms finger-to-tentacle response
    Angle Accuracy<3° error across full 0°–120° range
    Grip Force≥0.5 N at 90° bend, measurable with spring scale
    Object DiversitySuccessfully grasp ≥5 different object geometries
    Battery Life≥30 min continuous operation per charge
    Durability≥300 full grip cycles without structural failure

    Completion milestones:

    3D Design (Autodesk Inventor)100%
    TPU Tentacle Fabrication90%
    PCB Design & Milling95%
    BLE Firmware100%
    System Integration & UR375%
    Final Testing & Documentation60%