Week 10: Applications and Implications
My final project is going to be a fun, wearable soft robotic tentacle.
What will it do?
It will move via expansion and contraction in response to sensors attached to the wearer.
Who's done what beforehand?
I have found very little prior research on this particular method of actuating soft robots. I have only found these two papers, which are by the same team:
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Soft material for soft actuators
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Describes the combination of ethanol and silicone to create a self-contained electrically-driven soft actuator
- 20% ethanol to 80% platinum cure silicone
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We used platinum-catalyzed two-part silicone rubber Ecoflex 00-50 (Smooth-On, PA, USA) as a matrix material and ethanol ≥ 99.5% (Sigma Aldrich, MO, USA) as an active phase change material. Properties of the silicone rubber are shown in Table 1 below.
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Material preparation involves thorough hand-mixing of 20 vol% of ethanol with silicone elastomer (first with part A for about 2 min, then mixed with part B for about 2 min). The material is ready-to-cast and ready-toprint after the preparation. Room temperature curing of the cast or 3D-printed part takes up to 3 h.
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A commercially available 0.25 mm diamter Ni-chrome resistive wire was used for electrically driven heating of the artificial muscle (i.e., for the actuation).
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To comply with the expansion of the actuator material, a helical spiral shape was chosen for the Ni–Cr wire. The wire was hand-wound on an 8 mm screw driver shaft as shown in Supplementary Fig. 6
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Functional properties of silicone/ethanol soft-actuator composites
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There has been a lot of other work with specifically dielectric elastomers, which are somewhat similar in that they're not pump-powered; however, I believe that other forms of dielectric elastomers are not suitable for my project, as their form (needing electrodes on both ends) and high-voltage requirement would be impractical. I'd still be interested in seeing if a negative ion generator could sub in as a source of voltage; however, I'm not sure what would serve as the second electrode.
What will you design?
I will design the mold for casting the tentacle in, a PCB for driving the nichrome wire, and a case for containing the PCB and the battery.
What materials and components will be used?
AND
Where will they come from?
AND
How much will they cost?
Part | Component | Price | Source |
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Mold: | Machinable wax, or possibly 3D printed PLA | 10 | Aalto Fab Lab |
Tentacle body: | Platinum cure Silicone: Ecoflex 00-50 (Smooth-On, PA, USA) | 44 | https://www.kaupo.de/shop/en/SILICONE-RUBBER-Platinum-Cure/ECOFLEX-SERIES/Ecoflex-00-30/ |
Ethanol (≥ 99.5% purity) | Unknown | Aalto Biofilea Lab | |
Ni-chrome resistive wire (0.25 mm diamter) | 10 | https://www.amazon.com/IIVVERR-Nichrome-0-25mm-Heater-calentador/dp/B07ZCXN29Q/ref=sr_1_2?dchild=1&keywords=nichrome+wire+.25&qid=1587148773&s=electronics&sr=1-2-catcorr | |
PCB: | Microcontroller - possibly an ATtiny45, tbd | 2 | https://www.digikey.com/product-detail/en/microchip-technology/ATTINY45-20SU/ATTINY45-20SU-ND/735466 |
FR-1 | 5 | Aalto Fab Lab | |
Battery: | Li-po battery (size tbd) | 30 | internet, price is very dependent on capacity |
Sensor: | Pressure-sensitive resistive sensor (tbd) OR | 5 | internet, price depends on sensor |
Temperature sensor (tbd) OR | 5 | internet, price depends on sensor | |
Some other fun sensor, depends on how the motion turns out | 5 | internet, price depends on sensor | |
Case: | Fabric OR | 15 | Eurokangas |
PLA OR | 5 | Aalto Fab Lab | |
Acrylic | 10 | Aalto Fab Lab |
Sources: Fab-lab inventory, biofilia lab, Eurokangas, Digi-Key
What parts and systems will be made?
Every 'part' listed above.
What processes will be used?
CNC milling, 3D printing (potentially), mold making and casting, 2D design, embedded programming, electronic design.
What questions need to be answered?
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How do we actually work with the silicone-ethanol mixture?
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How do we keep the circuit small, discrete, and wearable?
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How do we design the tentacle mold?
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How will we source certain materials (ethanol)?
How will it be evaluated?
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Functionality - does it work?
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Construction quality - is it well constructed?
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Finishing - does it look nice?