Multi-Role Armament & Ammunition System (MRAAS) Weapon …€¦ · Control Request For Proposal:...

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Multi-Role Armament &Ammunition System (MRAAS)

Weapon StabilizationAssessment

United Defense L.P.Armament Systems Division

Minneapolis, MN

Gregory S. JohnsonJerry C. Chang

Jeffrey V. IrelandRickie L. Stuva

Thomas R. Williams

37th Gun and Ammunition NDIA Symposium

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Contents

• Background• Main Objectives• Requirements• Vehicle Dynamics Model• Gun Pointing Control System Model• Stochastic Pointing Error Estimation• Platform Stability Analysis• Gun Pointing Stiffness Study• Conclusions

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Background

• U.S. Army Transformationrequires transition to highlytransportable fighting force.

• The Future Combat System (FCS)is the intended objective -“system of systems” to meet avariety of missions.

• Multi-Role Armament &Ammunition System (MRAAS)under development by U.S. ArmyARDEC to meet FCS LOS DirectFire and BLOS/NLOS IndirectFire lethality requirements.

MRAAS Multi-Mission ATD features:• Turret Mission Module for integration

into light vehicle• 105 mm cannon with swing chamber• CTA munitions for direct/indirect fires• LOS kills out to 4-5 km, BLOS kills out

to 50+ km• C-130 transportable, with 19 ton total

system weight.

MRAAS Study ConceptMRAAS Study Concept

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Main Objectives

As part of 6 Month MRAAS Concepting Study Contract:

• Determine system dynamics impact of integrating a largecaliber gun system onto a lightweight ground vehicle.

• Evaluate weapon stabilization performance of MRAAS,including sensitivity to:• Gun unbalance due to CG offset from trunnion axis.• Disturbances due to vehicle motion over terrain.

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• Per the MRAAS Turret Mission Module – WeaponControl Request For Proposal:• Fire Control System shall support LOS engagements under

dynamic conditions with no greater than θtotal mils error, 1 sigmaRoot Mean Square (RMS).

• Muzzle stabilization error shall be no more than θstab mils RMS.• Indirect fire requirements less stringent.

• Dynamic Condition Assumptions:• Fire On The Move vehicle speed varied 5 to 30 mph.• APG Munson Gravel Course and RRC-9 Stabilization Bump

Course terrain models used to span roughness.

Requirements

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Vehicle Dynamics Model:Vehicle Concepting

Key Assumptions:• MRAAS turret concept mounted in mid and rear locations on wheeled

chassis, with balanced/unbalanced armament (CG forward of trunnion).• Appropriate mass property and space claim adjustments made:

UnbalanceMost Signicant

Effect ForStabilization

Concept Turret Location Gun UnbalanceI Rear UnbalancedII Rear BalancedIII Mid UnbalancedIV Mid Balanced

Unbalanced GunWEAPON COMPARTMENT CREWPOWER

PACKWEAPON

COMPARTMENTWEAPON

COMPARTMENT CREWCREWPOWER PACK

POWER PACK

WEAPON COMPARTMENT

CREW POWER PACK

WEAPON COMPARTMENT

WEAPON COMPARTMENT

CREWCREW POWER PACK

POWER PACK

Concepts I & II Concepts III & IVTrunnion Brg

Tipping Assy CG

Balanced Gun

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Vehicle Dynamics Model:DADS Development

Key Vehicle Dynamics Assumptions:• DADS rigid body chassis model.• Simplified wheeled suspension model

capturing hydropneumatic non-linearstiffness and damping characteristics• Heave natural freq. ~ 1.5 Hz (translation)• Pitch natural freq. ~ 0.75 Hz (rotation)• Near critical damping• Tire stiffness & damping.

Fn1Fn2Fn3Fn4

Fs4 Fs3 Fs2 Fs1

Traverse Brg Axis Trunnion Brg

Axis

HSU Stiffness, Damping

Tire StiffnessW

Fn1Fn2Fn3Fn4

Fs4 Fs3 Fs2 Fs1

Traverse Brg Axis Trunnion Brg

Axis

HSU Stiffness, Damping

Tire StiffnessW

Vehicle Dynamics Free Body DiagramVehicle Dynamics Free Body Diagram

MRAAS DADS Wheeled Suspension ModelModified HSU Stiffness Characteristics

-20000

-15000

-10000

-5000

0

5000

10000

15000

20000

-20.0 -15.0 -10.0 -5.0 0.0 5.0 10.0 15.0

Wheel Travel [in]

Sp

rin

g F

orc

e [l

b]

Front Stations

Rear Stations

Jounce Rebound

Approx. Static Position

Bump Stops

MRAAS DADS Vehicle Suspension ModelModified HSU Damping Characteristics

-1500

-1000

-500

0

500

1000

1500

2000

-60 -50 -40 -30 -20 -10 0 10 20

Wheel Travel Velocity [in/s]

Dam

pin

g F

orc

e [l

b]

Front Stations

Rear Stations

Jounce

Rebound

Suspension Stiffness CharacteristicsSuspension Stiffness Characteristics Suspension Damping CharacteristicsSuspension Damping Characteristics

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Vehicle Dynamics Model:DADS Platform Disturbance Estimate

• Vehicle Pitch RateDisturbance PowerSpectral Density(PSD)

MRAS Gun Pointing Disturbance: Concept IATC RRC-9 Stabilization Bump Course, 9/01 Model Update

0.0000001

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

0.1 1 10 100

Frequency [Hz]

Hea

ve A

ccel

erat

ion

Dis

turb

ance

PS

D [

g2 /H

z]

5 MPH

10 MPH20 MPH

30 MPH


0.01

0.1

1

10

100

1000

10000

100000

0.1 1 10 100

Frequency [Hz]

Pitc

h R

ate

Dis

turb

ance

PS

D [

mra

d2 /s

2 /Hz] 5 MPH

10 MPH

20 MPH

30 MPH

• Vehicle HeaveAccelerationDisturbance PSD

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Gun Pointing Control System Model:MATRIXx Development

• Preliminary Elevation GPCS Model created in MATRIXx.• Outer Gyro Rate P+I Loop (inertial) wrapped around

Inner Motor Rate P+I loop (relative).• MATRIXx model includes:

• Plant dynamics with variable drive compliance, gear reduction• P+I compensation with notch filter• Hull rate feed forward sensor with roll-off.

MATRIXx Elevation GPCS Block DiagramMATRIXx Elevation GPCS Block Diagram

10

0.1 1 10 100

Frequency [Hz]

-30

Gai

n [d

B]

Dist Rejection W/OutHull Rate Feed Fwd

Gun Pointing Control System Model:GPCS Disturbance Rejection Estimate

• MATRIXx model usedto estimate platformdisturbance rejectiontransfer function.

• Hull rate feed forwardprovides substantiallygreater rejection at lowfrequency.

0.1 1 10 100

Frequency [Hz]

Gai

n [d

B]

-80

Dist Rejection WithHull Rate Feed Fwd

)(

)()(

ωθ

ωθω

dist

errG &&

=)(

)()(

ωθ

ωθω

dist

errG &&

=

11

0 dB

|G(ω)|

ωbw

TERRAIN PROFILE

VEHICLEDYNAMICS

MODEL

GPCSELEVATIONRESPONSE

RMS

POWERSPECTRALDENSITY

GPCS ELEV.RATE LOOP

DISTURBANCEREJECTION

T.F.

HEAVEDISTURBANCE

)(tzT&&

PITCHDISTURBANCE

)(tvθ&&)(ωθdistS &VEHICLE CHARACTERISTICS:

- GEOMETRY- MASS PROPERTIES- SUSPENSION STIFFNESS- SUSPENSION DAMPING

bwω

ELEV. RATEDISTURBANCE PSD

)()(

)(ωθωθ

ωdisterrG &&

=

RMSθ

GPCS ELEV RATELOOP BANDWIDTH

ELEVATION 1σPOINTING

ACCURACY

ESTIMATED GPCSREJECTION RESPONSE

)( xZ

0 dB

|G(ω)|

ωbw

TERRAIN PROFILE

VEHICLEDYNAMICS

MODEL

GPCSELEVATIONRESPONSE

RMS

POWERSPECTRALDENSITY

GPCS ELEV.RATE LOOP

DISTURBANCEREJECTION

T.F.

HEAVEDISTURBANCE

)(tzT&&

PITCHDISTURBANCE

)(tvθ&&)(ωθdistS &VEHICLE CHARACTERISTICS:

- GEOMETRY- MASS PROPERTIES- SUSPENSION STIFFNESS- SUSPENSION DAMPING

bwω

ELEV. RATEDISTURBANCE PSD

)()(

)(ωθωθ

ωdisterrG &&

=

RMSθ

GPCS ELEV RATELOOP BANDWIDTH

ELEVATION 1σPOINTING

ACCURACY

ESTIMATED GPCSREJECTION RESPONSE

)( xZ

Stochastic Pointing Error Estimation


0.01

0.1

1

10

100

1000

10000

100000

0.1 1 1 0 100

Frequency [Hz]

Pit

ch R

ate

Dis

turb

ance

PS

D [m

rad2 /s

2/H

z] 5 MPH

10 MPH

20 MPH

30 MPH

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MRAAS Gun Pointing Control Bandwidth AnalysisConcept I (Unbalanced Gun, Rear Turret)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.1 1 10 100

Elevation Rate Loop Bandwidth [Hz]

Pre

dic

ted

Ele

vati

on

Po

inti

ng

Acc

ura

cy

[mra

d, R

MS

]

5 MPH (Gravel Course)

5 MPH (Bump Course)


10 MPH (Bump Course)





Stochastic Error Estimation:Concept I Sensitivity to Terrain, Speed

5

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MRAAS Gun Pointing Control Bandwidth AnalysisConcept II (Balanced Gun, Rear Turret)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.1 1 10 100


Pre

dic

ted

Ele

vati

on

Po

inti

ng

Acc

ura

cy

[mra

d, R

MS

]


5 MPH (Bump Course)







Stochastic Error Estimation:Concept II Sensitivity to Terrain, Speed

5

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Platform Stability Analysis

• Stochastic method appropriate forconcept-level parametric trades.• Allows rapid assessment of multiple

simulation scenarios.• Assumes load motion does not

significantly influence base motion(gun and chassis are uncoupled).

• Next level of fidelity involvescoupling MATRIXx pointing controlmodel with DADS suspension modelvia DADS/Plant.

• Resulting “Platform Stability” modelused to:• Analytically verify stochastic method• Estimate gun drive power requirements

using Concepts I & II.

MRAAS MATRIXx GPCS ModelMRAAS MATRIXx GPCS Model

MRAAS Rigid Body DADS ModelMRAAS Rigid Body DADS Model

DADS/PlantDADS/PlantControl Forces& Torques

MotionFeedback


MRAAS Rigid Body DADS ModelMRAAS Rigid Body DADS Model

DADS/PlantDADS/PlantControl Forces& Torques

MotionFeedback

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MRAAS Gun Pointing Control Bandwidth AnalysisConcept II (Balanced Gun, Rear Turret)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

1 10 100


Pre

dic

ted

Ele

vati

on

Po

inti

ng

Acc

ura

cy [

mra

d,

RM

S]

5 MPH (Bump Course)




30 MPH (Bump, MATRIXx)



5 MPH (Bump. MATRIXx)

STOCHASTIC

DADS/PLANT

METHOD

1 10 100


Platform Stability Analysis:Stochastic Method Verification, Concept I

• Unbalanced Gun

• Balanced Gun

MRAAS Gun Pointing Control Bandwidth AnalysisConcept I (Unbalanced Gun, Rear Turret)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

1 10 100


Pre

dic

ted

Ele

vati

on

Po

inti

ng

Acc

ura

cy

[mra

d, R

MS

]

5 MPH (Bump Course)




5 MPH (Bump. MATRIXx)




STOCHASTIC

DADS/PLANT

METHOD

1 10 100


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Platform Stability Analysis:Elevation Drive Power Estimation

MRAAS Weapon Stabilization Power Estimation RRC-9 Bump Course, 10 Hz 1st Mode, 70% Assumed Overall Efficiency

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

0 5 10 15 20 25 30 35

Vehicle Speed [mph]

To

tal M

oto

r P

ow

er R

equ

ired

[HP

]

Slew Accel = 1.0 rad/s2






Model I: Unbalanced Gun

Model II: Balanced Gun

Low Slew Accel

Med Slew Accel

High Slew Accel

Low Slew Accel

Med Slew Accel

High Slew Accel

MRAAS Weapon Stabilization Power Estimation RRC-9 Bump Course, 10 Hz 1st Mode, 70% Assumed Overall Efficiency

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

0 5 10 15 20 25 30 35

Vehicle Speed [mph]

To

tal M

oto

r P

ow

er R

equ

ired

[HP

]







Model I: Unbalanced Gun

Model II: Balanced Gun

Low Slew Accel

Med Slew Accel

High Slew Accel

Low Slew Accel

Med Slew Accel

High Slew Accel

( ) maxω×++= stabaccelunbalanceTotalP ΤΤΤ

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MRAAS Gun Pointing Stiffness SensitivityEffective First Mode vs Gun Drive Stiffness

0

1

2

3

4

5

6

7

8

1.00E+05 1.00E+06 1.00E+07 1.00E+08 1.00E+09 1.00E+10 1.00E+11

Effective Drive Stiffness (in-lb/rad, Actuator+Mount Lugs+Turret)

Short

Long

Short WithTube Sprt.

Gun Mount Configuration

Gu

n P

oin

tin

g F

irst

Mo

de

Effective Drive Stiffness

MRAAS Gun Pointing Stiffness SensitivityEffective First Mode vs Gun Drive Stiffness

0

1

2

3

4

5

6

7

8

1.00E+05 1.00E+06 1.00E+07 1.00E+08 1.00E+09 1.00E+10 1.00E+11

Effective Drive Stiffness (in-lb/rad, Actuator+Mount Lugs+Turret)

Short

Long

Short WithTube Sprt.

Gun Mount Configuration

Gu

n P

oin

tin

g F

irst

Mo

de

Gu

n P

oin

tin

g F

irst

Mo

de

Effective Drive Stiffness

Gun Pointing Stiffness Study

• Minimum 1st natural frequency of the gun pointing system isconstrained by the controller bandwidth.

• The gun pointing system natural frequency is determined by theflexibility of: Gun Drive Actuators, Turret, Gun Mount, Cannon

A parametric study using aNASTRAN FEM was usedto investigate first modesensitivity to:

• Elevation Drive Stiffness• Mount/Cannon Stiffness• Mount Extension Length• Mount Bearing Locations

NASTRAN Armament Finite Element ModelNASTRAN Armament Finite Element Model

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DADS/Plant Flexible BodyDemonstration

Active Gun Pointing WithArmament Structural Flexure

APG RRC-9 Stabilization Course

Platform Stability Analysis Demo:DADS/Plant w/Stabilized Flex Body

MRAAS DADS Model withFlexible Body Armament

MRAAS DADS Model withFlexible Body Armament

DADS/PlantDADS/Plant


Control Forces& Torques

MotionFeedback

NASTRAN Modal AnalysisNASTRAN Modal Analysis

DADS Flexible BodyTranslator

DADS Flexible BodyTranslator

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Platform Stability Analysis Demo:DADS/Plant - Stabilized Flexible Body

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Conclusions

• Stochastic error estimation method provided rapid concept-levelgun pointing performance estimation.

• Reducing gun CG offset from trunnion could reduce req’mts for:• Bandwidth & pointing stiffness by up to 25%• Maximum drive power by up to 50%• Trunnion vertical accelerometer (vertical acceleration feed forward).

• Parametric FEA modeling used for early estimation of optimalgun pointing component stiffnesses.

• Coupled modeling approach provided improved fidelity byleveraging subsystem models.

• Next step is to incorporate a Muzzle Reference Sensor witharmament flexure response in the pointing control model.

• Using this approach, the disturbance rejection benefit of an activesuspension system can also be evaluated.

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Acknowledgements

• Study Co-Authors:• Jerry Chang, DADS Vehicle Dynamics• Rick Stuva, Gun Pointing Control Analysis• Jeff Ireland, Tech Consulting/Pointing Stiffness• Tom Williams, Parametric FEA

• This study was initiated and funded by the U.S. ArmyARDEC under Contract DAAE30-00-C-1060.

• The authors would like to thank Steven McDonald,Roger Kent, Ramon Espinosa, and Thomas Louzeiro atPicatinny Arsenal; and Stephen Krupski at Benet Labsfor their timely assistance, suggestions, and feedback.

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