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  • DESIGN, SIMULATION AND TESTING OF SHRIMP ROVER USING RECURDYN

    Shivesh Kumar, Raghavendra S, Mihir R Bhagat, Gangadharan K V,Department of Mechanical Engineering

    12th Symposium on Advance Space Technologies in Robotics and Automation,ESA / ESTEC, Noordwijk, The Nethelands

    NATIONAL INSTITUTE OFTECHNOLOGY KARNATAKA

    Surathkal, INDIA

  • CONTENT

    Introduction- Shrimp

    - RecurDyn

    Work in RecurDyn- Modeling of Shrimp

    - Dynamic simulation on various terrain profiles

    Shrimp: Manufacturing Experimental Validation Results & Discussions Conclusions

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • INTRODUCTION

    Rovers: Most suitable for planetary exploration

    Over 300 design concepts developed already

    Shifting trends: Long-term, reusable rovers

    Fewer solo-missions. Regular inclusion of a greater bigger objective.

    Rover deliverables increase:

    Long range Greater mobility Low power consumption High modularity Ease of control

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • SHRIMP ROVER

    Innovative 6 wheeled rover

    Design at the Swiss Federal Institute of Technology (EPFL), Lausanne

    Design objective: Long-range mission for Martian exploration

    Fully functional prototype was demonstrated at ESTEC (2000)

    Image: EPFL

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • SHRIMP ROVER: KEY FEATURES

    6 motorized wheels

    2 parallel bogies, front and rear forks

    Passive control

    Excellent mobility:

    - Obstacle climbing - 2 x wheel dia.

    - Topple resistance - Upto 40 degrees

    - Pure steering possible

    Image: EPFL

    (a)

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • RECURDYN

    Multi-body dynamics software

    Advantages over other softwares:

    - No more excessive simplification

    - High solving efficiency

    - Good solving stability

    Equations of motion theory in recursive formation

    High precision, fast solving.

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  • MODELING OF SHRIMP

    Initial design based on SHRIMP III by BlueBotics (www.bluebotics.com)

    Design made in CATIA V5

    Imported to RecurDyn and joints defined

    Type of JointType of Joint No. of Joints

    Type of Actuation

    Revolute joints

    Between body and wheels

    6 Active

    Revolute joints

    In front fork 4+1 4 Passive, 1 Active

    Revolute joints In rear fork 1 Active

    Revolute joints

    In right parallel bogie

    6 Passive

    Revolute joints

    In left parallel bogie

    6 Passive

    Other parameters defined as well:

    Wheel speed: 30 rpm

    Friction: static = 0.5 dynamic = 0.3 Tire and road surface properties:

    Spring coeff. = 1000 N.mm

    Damping coeff. = 1

    Damping friction coefficient = 0.9

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

    http://www.bluebotics.comhttp://www.bluebotics.com

  • DYNAMIC SIMULATION

    Kinematic and Dynamic simulation done using the multi-body dynamics solver of RecurDyn

    Simulation time and time steps chosen suitably

    The rover capabilities are tested on 3 types of terrains:

    - Ability to climb steps

    - Ability to climb a inclined surface

    - Ability to adapt passively with concave/convex terrains

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • CLIMBING STEPS

    Obstacle: Step

    Step size: 200 mm

    Under review: Torque requirements of the wheels

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • CLIMBING STEPSFRONT WHEEL

    REAR WHEEL

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • CLIMBING INCLINATION

    Obstacle: Slope

    Slope inclination: 40 degree

    Under review: Torque requirements of the wheels

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • CLIMBING INCLINATIONFRONT WHEEL

    REAR WHEEL

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • CURVED SURFACE ADAPTABILITY

    Shrimp makes use of a passive suspension system

    Its is tested to check its adaptability to curved surfaces.

    Ex.: Concave

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • TORQUE ANALYSIS

    Wheel-Bogie Joint Position Max Torque (Kg-cm)

    Front Fork 32.1

    Right Front 7.5

    Right Rear 7.4

    Left Front 7.0

    Left Rear 6.8

    Rear Fork 16.3

    Maximum torque required is close to 32.1 kg-cm

    Factor of Safety: 1.25

    Hence, Torque requirement becomes 40.1 kg-cm

    Available option: 45 kg-cm motors.

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • SHRIMP: MANUFACTURING

    Major Parts

    - Main body

    - Parallel bogies

    - Front & Rear fork

    - Electronics sub-system

    Built in-house at NITK

    Undergraduate project: Resources and facilities greatly constrained.

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • MAIN BODY

    Twin Alumnium pentagons form the base

    Supporting aluminium blocks:

    - To join the two plates

    - Support the load

    - Mounting point for revolute joints

    Bearings used for revolute joints

    Similar setup for the front fork

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • PARALLEL BOGIE

    Aluminium bogies mounted on either side of the rover

    Frames of C-section links that form a couple

    Mounted on freely rotating central pivot

    NOTE: Left and right bogie should be greatly identical to avoid mismatch in travel

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • FRONT & REAR FORKS

    Wheel mounted at the forks

    Front fork is similar to a 4 bar mechanism; wheel made to travel upward when it encounters obstacle

    Steering is achieved using servos whose axis is perpendicular to the ground and the axis of wheels

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • ELECTRONICSKey Features

    2 parts: Base station & On-board control system

    Completely wireless control and data transmission using Xbee module

    Wireless video feed

    2 ATMEGA16 processors in master slave configuration

    Light and portable LiPo battery along with battery protection circuit

    Interactive GUI using Matlab

    User

    MATLAB based GUI

    Intel Core 2 DuoProcessor (2.4 GHz)

    based PC

    Sensor DataLive Video feed

    Rover Control Commands

    Wireless Xbee Module (Transmitter)

    USB TV

    Tuner

    RFReceiver

    A/V feed FTDI based USB - UART bridge

    Wireless Xbee Module (Receiver)

    Atmega 16 based developer board (AVRiboard2.0)

    RFTransmitter

    AVR-iboard

    2.0

    Master Controller Slave Controller

    3 units of:8-28 V, 5A dual DC motor

    drivers with current sensing

    Right Bogie

    Left Bogie

    Front & Rear Fork

    Front & Rear ForksServo for Steering

    Servo Pod2 servos

    SHARP IR Range Sensor

    Wireless Video Camera

    BASE STATION

    ON-BOARD CONTROL SYSTEM

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • EXPERIMENTAL VALIDATION

    Process

    Make the rover traverse obstacle paths to prove capabilities

    Measure armature current drawn by the motors and thus, estimate the driving torque requirements

    Compare Driving Torque v/s Time graphs with those of RecurDyn

    Obstacles

    Step Test:8cm height

    Slope Test:30 degree inclination

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • MEASURING THE TORQUEHow to calculate torque?

    = Kt I

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

    THE EXPERIMENTS

  • VALIDATION RESULTS

    Step Test

    Front Wheel

    Mean Absolute Percentage Error (MAPE) = 35.62%

    Slope Test

    Rear Wheel

    Mean Absolute Percentage Error (MAPE) = 42.87%

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • JUSTIFICATION FOR ERRORS

    MAPE typically varied between 35 - 45 % for all cases.

    Effects of electrical DC drive model not included in our simulation. Non-linearities like BEMF voltage, friction between bearings, etc affect the system

    Incorrect data / estimation used in modeling: friction in revolute joints, contact friction, etc

    Mismatch between modeled and actual mass-inertia properties

    Simplified model: Nuts, bolts, clamps, etc not modeled

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • CONCLUSIONS

    Modeling & dynamic simulation of Shrimp through RecurDyn

    Virtual testing of rover on different terrains

    RecurDyn helped in selecting actuators for given payload requirements

    Experimental validation gave satisfactory results

    RecurDyn can be further exploited by better handling of problem at hand

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • ACKNOWLEDGEMENTS

    Mr. B Sridhar, Director of Function Dynamics India Pvt. Ltd.

    for issuing provisional licenses of RecurDyn for our project.

    NITK Alumni Associationfor providing a soft loan to attend this conference.

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

  • THANK YOU!

    ASTRA 2013: ESA / ESTEC, Noordwijk, The Netherlands

    Please contact:[email protected]