Resistive Force Measurement Apparatus

Design Proposal Presentation

MAE 156A, Group 24

Sponsors: Dr.Nicholas Gravish & Dr. Michael Tolley

Emily Brown, Dylan McCulloch, Richard Vallejo Jr, Hrag Ekmekjian

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Contents

Problem Definition

Risk Reduction

Initial Design Decisions

Remaining Design Decisions

Final Design Proposal

Project Management

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2

Problem Definition

• Understanding resistive forces in sand
• Aid in bio-inspired robot design
• Variability in the real environment
• Large drag and lift forces
• Differences across beach terrain
• Soil characterization apparatus
• Specific to scale of robot (intruder)
• Measure resistive torque as rotated

3

Emily Brown

Photograph of the robot showing the underactuated appendages and terrafoils [2].

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Project Specifications

Functional Requirements

• Measure force/torque with intruder
• Operable in water
• Automatic data-logging

Constraints

• Corrosion, water, and sand resistant
• Stable in sand and small waves
• Operable by 2 people
• Portable and lightweight
• Budget:
• $1,000 - equipment and parts
• $600 - shared shop expenses

4

Emily Brown

Concept sketch from sponsor specifications (from sponsor presentation).

Risk Reduction

Apparatus Performance

5

Risk Reduction

• Hardware test of frame with intruder rotation and penetration mechanism
• Success Areas:
• Overall alignment and stability
• Ease of assembly
• Lightweight and easily transportable
• Improvement Areas:
• Apparatus feet (holding)
• Overall height
• Overcoming environmental forces
• Penetration with manual intruder
• Sand in bushings

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6

Richard Vallejo Jr

Initial Design Decisions

Considerations & Analysis

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Initial Design Decisions

• Tripod apparatus frame
1. Stability
2. Standardization
3. Production & Assembly
• Resistive torque measurement
• Strain gauges
• Analog torque wrench and encoder
• Electronics package
• Bushings & Bearings

8

Emily Brown

CAD Model for final risk reduction test apparatus.

Main Tripod Leg

Upper Bearing Hub

Leg Extender

Sand Foot

Lower Bearing Hub

Bearing Support

Mid Leg Joint

Force/Torque Sensing

• Force-Torque sensor in-line with intruder shaft
• Measure axial loads (forces and torques)
• Force measurement is low priority
• Housing to protect from sand and water

9

Dylan McCulloch

Force-Torque sensor intended functionality and position

Electronics Package/Operation

• Arduino Mega for data collection
• Adafruit Data Logging Shield and Bluetooth Module for data storage
• Sensor package including
• GPS
• Temperature/humidity
• Soil moisture
• Intruder height (analog input)
• TBD
• Force/torque sensor
• Rotary encoder

10

Richard Vallejo Jr.

Initial wiring diagram for data collection package

Bushings & Bearings

• Bushing Type
• Stainless Steel Bushing with PTFE Liners (Self-lubricating)
• Concerns
• Sand Infiltration
• Water Exposure
• Rotational and Vertical Motion
• Considerations
• Low Friction
• Corrosion Resistant

11

Hrag Ekmekjian

Stainless Steel Bushing (PTFE Lined)

Remaining Design Decisions

Adjustments & Integration

12

Apparatus Frame Adjustments

13

Emily Brown

Comparisons of height of intruder handle before sand penetration.

Overall Height

Overcoming Environmental Forces

Stainless Steel Bushing

PTFE Fabric, Self-lubricating.

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Apparatus Feet

Apparatus used to examine underwater flow velocity (at left) and staked into the sand floor with a pin through a post attached to the main leg (at right).

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Force/Torque Sensing

Critical decision: OTS or In-House Force/Torque sensing solution

• OTS sensor: precision, lower risk, technical documentation and support
• In-House sensor: available in project budget, customizability

14

Dylan McCulloch

Left: Prebuilt torque sensor (McMaster-Carr)

Right: Torque measurement using strain gages (Binsfield)

Force/Torque Sensing

In-House Sensor Considerations:

• Strain gage design:
• Strain gages in cross configuration shaft axis measures torque
• Strain of 0.01-0.0001
• Load cell design:
• Solution using load cells limits unreliability of strain gages

15

Dylan McCulloch

Left: Prebuilt torque sensor (McMaster-Carr)

Right: Torque measurement using strain gages (Binsfield)

Rotary Encoder Implementation

Ideal: Hollow Bore Incremental Rotary Encoder

• Accommodates axial sliding of intruder bar
• Simple mounting to apparatus frame
• Often dust-tight
• Can be expensive ($200-$400)

Other options

• Belt/gear driven encoder meshed with intruder shaft
• Remove encoder altogether
• Visual protractor around intruder shaft, manually record change and angle each test

16

Richard Vallejo Jr

Sample hollow bore incremental rotary encoder: HB6M from US Digital

Execution Timeline

17

Dylan McCulloch

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Design/Fabrication Timeline:

First draft of individual component designs: 4/15

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Team design review: 4/21

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Manufacturing: 4/21-5/2

Final Design Proposal

Summary & Execution

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Proposed Design

Key Dimensions:

• Frame Height: 0.914 m (3ft)
• Frame Footprint: ~0.838 m x 0.965 m (2.75 ft x 3.166 ft)
• Intruder Height range: 0.965m (3.166 ft) to 1.219 m (48 in)
• Elbow Height

Key Changes

• More parts for initial manufacturing/assembly
• Splits into Bearing Column and Main Legs for easier storage/transport
• Assembly with fasteners

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Bearing Column

Tripod Leg

Electronics Box

Sand Feet (TBD)

Preliminary CAD for final Resistive Force Measurement Apparatus

Richard Vallejo Jr

Design Breakdown

20

Richard Vallejo Jr

Bottom Bearing Hub Support

Bottom Flat Bracket

Bearing Hub

Top Flat Bracket

Top Bearing Hub Support

Electronics Box

Bearing Column Support

Bottom Hub Sheet

Bearing Housing

Top Hub Sheet

Main Leg

Tripod Leg Breakdown

Bearing Column Breakdown

Bearing Hub Breakdown

Components List - Purchasing

• Frame assembly
• 1010 Aluminum 6063-T6 T-slot extrusion
• Aluminum ⅛ in sheet metal
• Aluminum 6061 square stock
• Steel shaft for Intruder
• Various fasteners
• Stainless Steel PTFE-Lined Bushing
• Data Logging Electronics
• Arduino Mega and peripherals
• Environmental sensors
• Rotary Encoder
• Force/Torque Sensors

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Hrag Ekmekjian

Stainless Steel Bushing (PTFE Lined)

Steel Shaft

Purchasing Timeline

• This week (Week 2, 4/7 - 4/11)
• Preliminary data logging electronics (not including encoder and force/torque sensor)�
• Weeks 3-4
• Initial assembly materials
• Tripod Frame Materials
• Steel Intruder Shaft
• Apparatus Feet Materials
• Bushings
• Force torque sensor and rotary encoder

22

Hrag Ekmekjian

Components List - Machining

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Preliminary CAD Model for final apparatus design

Emily Brown

Engineer Feedback

• Bracket design to split bearing column and main legs
• Easier than welding
• Difficult angles to achieve
• Sheet metal
• T-slot cuts and bolts
• Improved breakdown
• Appeases initial constraint

24

Emily Brown

Bottom Bearing Hub Support

Bottom Flat Bracket

Main Leg

Tripod Leg Breakdown

Bearing Column

Tripod Leg

Electronics Box

Sand Feet (TBD)

Preliminary CAD for final Resistive Force Measurement Apparatus.

Project Management

Spring Quarter

25

Remaining Questions & Concerns

Intruder penetration

• Improving penetration ease and depth

Force/torque sensor

• Cost-benefit analysis over next week

Rotary encoder

Budget Concerns

26

Dylan McCulloch

Risk reduction testing at Mission Beach, hard-packed sand.

Gantt Chart

27

Dylan McCulloch

Current Gantt Chart as of April 6 (relevant sections only shown)

Thank you for watching!

Any questions?