P17027: Starfish Gripper
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Preliminary Detailed Design

Table of Contents

Team Vision for Preliminary Detailed Design Phase

Summarize:

Plans:

Achieved:

Prototyping, Engineering Analysis, Simulation

Soft Actuator Prototype

A mold was created and a soft actuator was formed using leftover Dragon Skin 10 material found in the lab. Pictures of the mold and limb are shown below.

The process for molding each limb is detailed in the following document. Soft-BodyFormingProcedure

Prototype Soft Actuator:

public/Detailed Design Documents/SoftActuator.jpg

Exploded View of Soft Actuator Pieces:

public/Detailed Design Documents/CAD/SoftActuator_ExplodedView.PNG

Pieces of the Mold Used for Forming:

public/Detailed Design Documents/CAD/SoftActuatorMold_Assembly.PNG

Feasibility: Prototyping, Analysis, Simulation

DC Motor Testing

A schematic hardware of DC motor was created and testing using H-bridge, couple push button and Arduino Uno for micro controller. A picture of actual testing shown below. And The process for Dc motor testing is detailed in the following document.

DC motor testing

public/Detailed Design Documents/Schematics/DC_motor.jpg

Actuation Pressure Test

The pressure generated by inflating a soft actuator was tested using compressed air, a series of flexible hoses, and a pressure gauge. The test procedure and results are documented in the following document.

Actuation Pressure Test

public/Detailed Design Documents/ActuationPressure_Example.jpg

Solenoid Valve Operation Test

A test was run to ensure that the solenoid valves ordered were operational, as well as to characterize their power consumption. The results of this test are shown in the following document.

Valve Power Characterization

public/Detailed Design Documents/Valve.jpg

Drawings, Schematics, Flow Charts, Simulations

Schematics Folder

Electrical Schematics

Top Level Electrical Schematic

Top Level Electrical Schematic PDF

See Schematics Folder for schematics of each individual component.

Hydraulic System Schematic

Hydraulic Schematic

Operation/Program Flowchart

Operation Flowchart

Pseudo Code

Pseudo Code

Mechanical System Flowchart

Mechanical Flowchart

Soft Actuator Mold Design & Drawings

Link to SolidWorks CAD Models

Link to PDF Drawings

Extension Mechanism Design

Below is an animation of the preliminary SolidWorks model created for the scissor extension mechanism. This model does not including mounting and mating surfaces or fasteners, but accurately represents the motion the mechanism will go through.

Extension Mechanism Model

Link to SolidWorks CAD Models

Component Selection and Purchasing

Links to all components can be found in the Bill of Materials on this page.

Selection

Pump

There were several choices that we considered for our pump, each with its own merits. Our decision-making process came down to whether we wanted a more expensive pump that was waterproof, but supplied just barely enough pressure, or if we wanted a less expensive pump that supplied more than enough pressure but was not designed to be submerged. The thermal management of each solution was also factored in, in the event that we had to enclose a pump in a sealed container underwater. After much consideration, we have chosen to purchase a Seaflo 21-Series Diaphragm Pump, shown below. This pump will supply more pressure than we require, and is relatively cheap. Past MSD teams have purchased similar diaphragm pumps and had an issue with thermal management. Since this pump will be operating underwater, our plan is to seal seams with an RTV silcone gasket material and then tape over the seams to waterproof the pump. This will allow the pump to be directly exposed to the water and should lend itself to thermal management

If this is not enough waterproofing for operation at depths of 1-2m, we will create an aluminum container and fill with marine grease. This method may prove an issue for thermal management.

Seaflo Diaphragm Pump

Soft Actuator Material

We have determined that Smooth-On's Dragon Skin 20 material will best suit our project. This material has a higher elastic modulus than the Dragon Skin 10 material that was used for our prototype. This will generate a higher pressure when actuating, and therefore be beneficial when the soft actuators are passively evacuated. A table of material properties is listed below.

Dragon Skin 20 Material Properties

Servomotor

A Hitec HS-5646WP High Torque Digital Servo has been chosen to drive the extension mechanism. This motor has an IP67 waterproof rating, meaning it is capable of withstanding water up to 1m in depth for a period of less than 30 minutes at a time. This may be enough waterproofing on its own for our application, but we will likely put this motor in a separate container with marine grease to ensure that it remains operational for the remainder of our time using it.

Servomotor

Torque: 157 oz-in @ 6V, 179 oz-in @ 7.4V

Speed: 0.20 s/60° @ 6V, 0.18 s/60° @7.4V

Waterproof Enclosure

Integra enclosures makes IP68 rated containers of various different sizes. This appears to be our best option for a waterproof container for our electronics. We still need to determine the exact size required, but are fairly confident in the brand. Below is shown an 8"x6"x4" container.

Enclosure

A team at Milwaukee School of Engineering used an Integra enclosure to house their electronics for an underwater ROV robotics project.

MSOE ROV Project

Ordered

(3) Solenoid valves - Aqua Tech AQT15SP

(1) 2 lb package of Dragon Skin 20 Silicone Material

Bill of Material (BOM)

Bill of Materials

Link to working document, including product comparison

BOM and Part Comparison.xlsx

BOM_10-30-16.pdf

Plans for next phase

Three Week Plans - Detailed Design Phase.pdf


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